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Shade avoidance helps plants maximize their access to light for growth under crowding. It is unknown, however, whether a priming shade avoidance mechanism exists that allows plants to respond more effectively to successive shade conditions. Here, we show that the shade-intolerant plant Arabidopsis can remember a first experienced shade event and respond more efficiently to the next event on hypocotyl elongation. The transcriptional regulator PHYTOCHROME-INTERACTING FACTOR 7 (PIF7) and the histone H3K27-demethylase RELATIVE OF EARLY FLOWERING 6 (REF6) are identified as being required for this shade avoidance memory. RNA-sequencing analysis reveals that shade induction of shade-memory-related genes is impaired in the pif7 and ref6 mutants. Based on the analyses of enrichments of H3K27me3, REF6 and PIF7, we find that priming shade treatment induces PIF7 accumulation, which further recruits REF6 to demethylate H3K27me3 on the chromatin of certain shade-memory-related genes, leading to a state poised for their transcription. Upon a second shade treatment, enhanced shade-mediated inductions of these genes result in stronger hypocotyl growth responses. We conclude that the transcriptional memory mediated by epigenetic modification plays a key role in the ability of primed plants to remember previously experienced shade and acquire enhanced responses to recurring shade conditions., (© 2024. The Author(s).)

The circadian clock entrained by environmental light-dark cycles enables plants to fine-tune diurnal growth and developmental responses. Here, we show that physical interactions among evening clock components, including PSEUDO-RESPONSE REGULATOR 5 (PRR5), TIMING OF CAB EXPRESSION 1 (TOC1), and the Evening Complex (EC) component EARLY FLOWERING 3 (ELF3), define a diurnal repressive chromatin structure specifically at the PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) locus in Arabidopsis. These three clock components act interdependently as well as independently to repress nighttime hypocotyl elongation, as hypocotyl elongation rate dramatically increased specifically at nighttime in the prr5-1 toc1-21 elf3-1 mutant, concomitantly with a substantial increase in PIF4 expression. Transcriptional repression of PIF4 by ELF3, PRR5, and TOC1 is mediated by the SWI2/SNF2-RELATED (SWR1) chromatin remodeling complex, which incorporates histone H2A.Z at the PIF4 locus, facilitating robust epigenetic suppression of PIF4 during the evening. Overall, these findings demonstrate that the PRR-EC-SWR1 complex represses hypocotyl elongation at night through a distinctive chromatin domain covering PIF4 chromatin., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Introduction: Ambient temperature-induced hypocotyl elongation in Arabidopsis seedlings is sensed by the epidermis-localized phytochrome B (phyB) and transduced into auxin biosynthesis via a basic helix-loop-helix transcription factor, phytochrome-interacting factor 4 (PIF4). Once synthesized, auxin travels down from the cotyledons to the hypocotyl, triggering hypocotyl cell elongation. Thus, the phyB-PIF4 module involved in thermosensing and signal transduction is a potential genetic target for engineering warm temperature-insensitive plants., Objectives: This study aims to manipulate warm temperature-induced elongation of plants at the post-translational level using phyB variants with dark reversion, the expression of which is subjected to heat stress., Methods: The thermosensitive growth response of Arabidopsis was manipulated by expressing the single amino acid substitution variant of phyB (phyB[G515E]), which exhibited a lower dark reversion rate than wild-type phyB. Other variants with slow (phyB[G564E]) or rapid (phyB[S584F]) dark reversion or light insensitivity (phyB[G767R]) were also included in this study for comparison. Warming-induced transient expression of phyB variants was achieved using heat shock-inducible promoters. Arabidopsis PHYB[G515E] and PHYB[G564E] were also constitutively expressed in rice in an attempt to manipulate the heat sensitivity of a monocotyledonous plant species., Results: At an elevated temperature, Arabidopsis seedlings transiently expressing PHYB[G515E] under the control of a heat shock-inducible promoter exhibited shorter hypocotyls than those expressing PHYB and other PHYB variant genes. This warm temperature-insensitive growth was related to the lowered PIF4 and auxin responses. In addition, transgenic rice seedlings expressing Arabidopsis PHYB[G515E] and PHYB[G564E] showed warm temperature-insensitive shoot growth., Conclusion: Transient expression of phyB variants with altered dark reversion rates could serve as an effective optogenetic technique for manipulating PIF4-auxin-mediated thermomorphogenic responses in plants., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Production and hosting by Elsevier B.V.)

Higher-order chromatin structure is critical for regulation of gene expression. In plants, light profoundly affects the morphogenesis of emerging seedlings as well as global gene expression to ensure optimal adaptation to environmental conditions. However, the changes and functional significance of chromatin organization in response to light during seedling development are not well documented. We constructed Hi-C contact maps for the cotyledon, apical hook and hypocotyl of soybean subjected to dark and light conditions. The resulting high-resolution Hi-C contact maps identified chromosome territories, A/B compartments, A/B sub-compartments, TADs (Topologically Associated Domains) and chromatin loops in each organ. We observed increased chromatin compaction under light and we found that domains that switched from B sub-compartments in darkness to A sub-compartments under light contained genes that were activated during photomorphogenesis. At the local scale, we identified a group of TADs constructed by gene clusters consisting of different numbers of Small Auxin-Upregulated RNAs (SAURs), which exhibited strict co-expression in the hook and hypocotyl in response to light stimulation. In the hypocotyl, RNA polymerase II (RNAPII) regulated the transcription of a SAURs cluster under light via TAD condensation. Our results suggest that the 3D genome is involved in the regulation of light-related gene expression in a tissue-specific manner., (© 2024 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.)

Background: Plant long non-coding RNAs (lncRNAs) have important regulatory roles in responses to various biotic and abiotic stresses, including light quality. However, no lncRNAs have been specifically linked to the Shade Avoidance Response (SAS)., Results: To better understand the involvement of lncRNAs in shade avoidance, we examined RNA-seq libraries for lncRNAs with the potential to function in the neighbor proximity phenomenon in Arabidopsis thaliana (A. thaliana). Using transcriptomes generated from seedlings exposed to high and low red/far-red (R/FR) light conditions, we identified 13 lncRNA genes differentially expressed in cotyledons and 138 in hypocotyls. To infer possible functions for these lncRNAs, we used a 'guilt-by-association' approach to identify genes co-expressed with lncRNAs in a weighted gene co-expression network. Of 34 co-expression modules, 10 showed biological functions related to differential growth. We identified three potential lncRNAs co-regulated with genes related to SAS. T-DNA insertions in two of these lncRNAs were correlated with morphological differences in seedling responses to increased FR light, supporting our strategy for computational identification of lncRNAs involved in SAS., Conclusions: Using a computational approach, we identified multiple lncRNAs in Arabidopsis involved in SAS. T-DNA insertions caused altered phenotypes under low R/FR light, suggesting functional roles in shade avoidance. Further experiments are needed to determine the specific mechanisms of these lncRNAs in SAS., (© 2024. The Author(s).)

Transcription factor ELONGATED HYPOCOTYL5 (HY5) is the central hub for seedling photomorphogenesis. E3 ubiquitin (Ub) ligase CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) inhibits HY5 protein accumulation through ubiquitination. However, the process of HY5 deubiquitination, which antagonizes E3 ligase-mediated ubiquitination to maintain HY5 homeostasis has never been studied. Here, we identified that Arabidopsis thaliana deubiquitinating enzyme, Ub-SPECIFIC PROTEASE 14 (UBP14) physically interacts with HY5 and enhances its protein stability by deubiquitination. The da3-1 mutant lacking UBP14 function exhibited a long hypocotyl phenotype, and UBP14 deficiency led to the failure of rapid accumulation of HY5 during dark to light. In addition, UBP14 preferred to stabilize nonphosphorylated form of HY5 which is more readily bound to downstream target genes. HY5 promoted the expression and protein accumulation of UBP14 for positive feedback to facilitate photomorphogenesis. Our findings thus established a mechanism by which UBP14 stabilizes HY5 protein by deubiquitination to promote photomorphogenesis in A. thaliana ., Competing Interests: Competing interests statement:The authors declare no competing interest.

Day length modulates hypocotyl elongation in seedlings to optimize their overall fitness. Variations in cell growth-associated genes are regulated by several transcription factors. However, the specific transcription factors through which the plant clock increases plant fitness are still being elucidated. In this study, we identified the no apical meristem, Arabidopsis thaliana-activating factor (ATAF-1/2), and cup-shaped cotyledon (NAC) family transcription factor ATAF1 as a novel repressor of hypocotyl elongation under a short-day (SD) photoperiod. Variations in day length profoundly affected the transcriptional and protein levels of ATAF1. ATAF1-deficient mutant exhibited increased hypocotyl length and cell growth-promoting gene expression under SD conditions. Moreover, ATAF1 directly targeted and repressed the expression of the cycling Dof factor 1/5 (CDF1/5), two key transcription factors involved in hypocotyl elongation under SD conditions. Additionally, ATAF1 interacted with and negatively modulated the effects of phytochrome-interacting factor (PIF), thus inhibiting PIF-promoted gene expression and hypocotyl elongation. Taken together, our results revealed ATAF1-PIF as a crucial pair modulating the expression of key transcription factors to facilitate plant growth during day/night cycles under fluctuating light conditions., (© 2024 John Wiley & Sons Ltd.)

Phytochrome-interacting factors (PIFs) are basic helix-loop-helix transcription factors that regulate light responses downstream of phytochromes. In Arabidopsis (Arabidopsis thaliana), 8 PIFs (PIF1-8) regulate light responses, either redundantly or distinctively. Distinctive roles of PIFs may be attributed to differences in mRNA expression patterns governed by promoters or variations in molecular activities of proteins. However, elements responsible for the functional diversification of PIFs have yet to be determined. Here, we investigated the role of promoters and proteins in the functional diversification of PIF1 and PIF4 by analyzing transgenic lines expressing promoter-swapped PIF1 and PIF4, as well as chimeric PIF1 and PIF4 proteins. For seed germination, PIF1 promoter played a major role, conferring dominance to PIF1 gene with a minor contribution from PIF1 protein. Conversely, for hypocotyl elongation under red light, PIF4 protein was the major element conferring dominance to PIF4 gene with the minor contribution from PIF4 promoter. In contrast, both PIF4 promoter and PIF4 protein were required for the dominant role of PIF4 in promoting hypocotyl elongation at high ambient temperatures. Together, our results support that the functional diversification of PIF1 and PIF4 genes resulted from contributions of both promoters and proteins, with their relative importance varying depending on specific light responses., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

The ethylene-regulated hypocotyl elongation of Arabidopsis thaliana involves many transcription factors. The specific role of MYC transcription factors in ethylene signal transduction is not completely understood. The results here revealed that two MYCs, MYC2 and MYC3, act as negative regulators in ethylene-suppressed hypocotyl elongation. Etiolated seedlings of the loss-of-function mutant of MYC2 or MYC3 were significantly longer than wild-type seedlings. Single- or double-null mutants of MYC2 and MYC3 displayed remarkably enhanced response to ACC(1-aminocyclopropane-1-carboxylate), the ethylene precursor, compared to wild-type seedlings. MYC2 and MYC3 directly bind to the promoter zone of ERF1, strongly suppressing its expression. Additionally, EIN3, a key component in ethylene signaling, interacts with MYC2 or MYC3 and significantly suppresses their binding to ERF1's promoter. MYC2 and MYC3 play crucial roles in the ethylene-regulated expression of functional genes. The results revealed the novel role and functional mechanism of these transcription factors in ethylene signal transduction. The findings provide valuable information for deepening our understanding of their role in regulating plant growth and responding to stress.

Cryptochromes (CRYs) act as blue light photoreceptors to regulate various plant physiological processes including photomorphogenesis and repair of DNA double strand breaks (DSBs). ADA2b is a conserved transcription co-activator that is involved in multiple plant developmental processes. It is known that ADA2b interacts with CRYs to mediate blue light-promoted DSBs repair. Whether ADA2b may participate in CRYs-mediated photomorphogenesis is unknown. Here we show that ADA2b acts to inhibit hypocotyl elongation and hypocotyl cell elongation in blue light. We found that the SWIRM domain-containing C-terminus mediates the blue light-dependent interaction of ADA2b with CRYs in blue light. Moreover, ADA2b and CRYs act to co-regulate the expression of hypocotyl elongation-related genes in blue light. Based on previous studies and these results, we propose that ADA2b plays dual functions in blue light-mediated DNA damage repair and photomorphogenesis., Competing Interests: Declaration of competing interest The authors declare that we have no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Arabidopsis plants adapt to warm temperatures by promoting hypocotyl growth primarily through the basic helix-loop-helix transcription factor PIF4 and its downstream genes involved in auxin responses, which enhance cell division. In the current study, we discovered that cell wall-related calcium-binding protein 2 (CCaP2) and its paralogs CCaP1 and CCaP3 function as positive regulators of thermo-responsive hypocotyl growth by promoting cell elongation in Arabidopsis. Interestingly, mutations in CCaP1/CCaP2/CCaP3 do not affect the expression of PIF4-regulated classic downstream genes. However, they do noticeably reduce the expression of xyloglucan endotransglucosylase/hydrolase genes, which are involved in cell wall modification. We also found that CCaP1/CCaP2/CCaP3 are predominantly localized to the plasma membrane, where they interact with the plasma membrane H + -ATPases AHA1/AHA2. Furthermore, we observed that vanadate-sensitive H + -ATPase activity and cell wall pectin and hemicellulose contents are significantly increased in wild-type plants grown at warm temperatures compared with those grown at normal growth temperatures, but these changes are not evident in the ccap1-1 ccap2-1 ccap3-1 triple mutant. Overall, our findings demonstrate that CCaP1/CCaP2/CCaP3 play an important role in controlling thermo-responsive hypocotyl growth and provide new insights into the alternative pathway regulating hypocotyl growth at warm temperatures through cell wall modification mediated by CCaP1/CCaP2/CCaP3., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Main Conclusion: Ambient concentrations of atmospheric nitrogen dioxide (NO 2 ) inhibit the binding of PIF4 to promoter regions of auxin pathway genes to suppress hypocotyl elongation in Arabidopsis. Ambient concentrations (10-50 ppb) of atmospheric nitrogen dioxide (NO 2 ) positively regulate plant growth to the extent that organ size and shoot biomass can nearly double in various species, including Arabidopsis thaliana (Arabidopsis). However, the precise molecular mechanism underlying NO 2 -mediated processes in plants, and the involvement of specific molecules in these processes, remain unknown. We measured hypocotyl elongation and the transcript levels of PIF4, encoding a bHLH transcription factor, and its target genes in wild-type (WT) and various pif mutants grown in the presence or absence of 50 ppb NO 2 . Chromatin immunoprecipitation assays were performed to quantify binding of PIF4 to the promoter regions of its target genes. NO 2 suppressed hypocotyl elongation in WT plants, but not in the pifq or pif4 mutants. NO 2 suppressed the expression of target genes of PIF4, but did not affect the transcript level of the PIF4 gene itself or the level of PIF4 protein. NO 2 inhibited the binding of PIF4 to the promoter regions of two of its target genes, SAUR46 and SAUR67. In conclusion, NO 2 inhibits the binding of PIF4 to the promoter regions of genes involved in the auxin pathway to suppress hypocotyl elongation in Arabidopsis. Consequently, PIF4 emerges as a pivotal participant in this regulatory process. This study has further clarified the intricate regulatory mechanisms governing plant responses to environmental pollutants, thereby advancing our understanding of how plants adapt to changing atmospheric conditions., (© 2024. The Author(s).)

Karrikins and strigolactones govern plant development and environmental responses through closely related signaling pathways. The transcriptional repressor proteins SUPPRESSOR OF MAX2 1 (SMAX1), SMAX1-like2 (SMXL2), and D53-like SMXLs mediate karrikin and strigolactone signaling by directly binding downstream genes or by inhibiting the activities of transcription factors. In this study, we characterized the non-transcriptional regulatory activities of SMXL proteins in Arabidopsis. We discovered that SMAX1 and SMXL2 with mutations in their ethylene-response factor-associated amphiphilic repression (EAR) motif had undetectable or weak transcriptional repression activities but still partially rescued the hypocotyl elongation defects and fully reversed the cotyledon epinasty defects of the smax1 smxl2 mutant. SMAX1 and SMXL2 directly interact with PHYTOCHROME INTERACTION FACTOR 4 (PIF4) and PIF5 to enhance their protein stability by interacting with phytochrome B (phyB) and suppressing the association of phyB with PIF4 and PIF5. The karrikin-responsive genes were then identified by treatment with GR24 ent-5DS , a GR24 analog showing karrikin activity. Interestingly, INDOLE-3-ACETIC ACID INDUCIBLE 29 (IAA29) expression was repressed by GR24 ent-5DS treatment in a PIF4- and PIF5-dependent and EAR-independent manner, whereas KARRIKIN UPREGULATED F-BOX 1 (KUF1) expression was induced in a PIF4- and PIF5-independent and EAR-dependent manner. Furthermore, the non-transcriptional regulatory activity of SMAX1, which is independent of the EAR motif, had a global effect on gene expression. Taken together, these results indicate that non-transcriptional regulatory activities of SMAX1 and SMXL2 mediate karrikin-regulated seedling response to red light., Competing Interests: Declaration of interests The authors declare no competing financial interests., (Copyright © 2024 The Author. Published by Elsevier Inc. All rights reserved.)

The interplay between microRNAs (miRNAs) and phytohormones allows plants to integrate multiple internal and external signals to optimize their survival of different environmental conditions. Here, we report that miR394 and its target gene LEAF CURLING RESPONSIVENESS (LCR), which are transcriptionally responsive to BR, participate in BR signaling to regulate hypocotyl elongation in Arabidopsis thaliana. Phenotypic analysis of various transgenic and mutant lines revealed that miR394 negatively regulates BR signaling during hypocotyl elongation, whereas LCR positively regulates this process. Genetically, miR394 functions upstream of BRASSINOSTEROID INSENSITIVE2 (BIN2), BRASSINAZOLEs RESISTANT1 (BZR1), and BRI1-EMS-SUPPRESSOR1 (BES1), but interacts with BRASSINOSTEROID INSENSITIVE1 (BRI1) and BRI1 SUPRESSOR PROTEIN (BSU1). RNA-sequencing analysis suggested that miR394 inhibits BR signaling through BIN2, as miR394 regulates a significant number of genes in common with BIN2. Additionally, miR394 increases the accumulation of BIN2 but decreases the accumulation of BZR1 and BES1, which are phosphorylated by BIN2. MiR394 also represses the transcription of PACLOBUTRAZOL RESISTANCE1/5/6 and EXPANSIN8, key genes that regulate hypocotyl elongation and are targets of BZR1/BES1. These findings reveal a new role for a miRNA in BR signaling in Arabidopsis., (© 2024 Society for Experimental Biology and John Wiley & Sons Ltd.)

Shade avoidance syndrome is an important adaptive strategy. Under shade, major transcriptional rearrangements underlie the reallocation of resources to elongate vegetative structures and redefine the plant architecture to compete for photosynthesis. BBX28 is a B-box transcription factor involved in seedling de-etiolation and flowering in Arabidopsis (Arabidopsis thaliana), but its function in shade-avoidance response is completely unknown. Here, we studied the function of BBX28 using two mutant and two transgenic lines of Arabidopsis exposed to white light and simulated shade conditions. We found that BBX28 promotes hypocotyl growth under shade through the phytochrome system by perceiving the reduction of red photons but not the reduction of photosynthetically active radiation or blue photons. We demonstrated that hypocotyl growth under shade is sustained by the protein accumulation of BBX28 in the nuclei in a CONSTITUTIVE PHOTOMORPHOGENESIS1 (COP1)-dependent manner at the end of the photoperiod. BBX28 up-regulates the expression of transcription factor- and auxin-related genes, thereby promoting hypocotyl growth under prolonged shade. Overall, our results suggest the role of BBX28 in COP1 signaling to sustain the shade-avoidance response and extend the well-known participation of other members of BBX transcription factors for fine-tuning plant growth under shade., Competing Interests: Conflict of interest statement None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Light and temperature are 2 major environmental factors that affect the growth and development of plants during their life cycle. Plants have evolved complex mechanisms to adapt to varying external environments. Here, we show that JASMONATE ZIM-domain protein 3 (JAZ3), a jasmonic acid signaling component, acts as a factor to integrate light and temperature in regulating seedling morphogenesis. JAZ3 overexpression transgenic lines display short hypocotyls under red, far-red, and blue light and warm temperature (28 °C) conditions compared to the wild type in Arabidopsis (Arabidopsis thaliana). We show that JAZ3 interacts with the transcription factor PHYTOCHROME-INTERACTING FACTOR4 (PIF4). Interestingly, JAZ3 spontaneously undergoes liquid-liquid phase separation (LLPS) in vitro and in vivo and promotes LLPS formation of PIF4. Moreover, transcriptomic analyses indicate that JAZ3 regulates the expression of genes involved in many biological processes, such as response to auxin, auxin-activated signaling pathway, regulation of growth, and response to red light. Finally, JAZ3 inhibits the transcriptional activation activity and binding ability of PIF4. Collectively, our study reveals a function and molecular mechanism of JAZ3 in regulating plant growth in response to environmental factors such as light and temperature., Competing Interests: Conflict of interest statement. The authors declare no conflict of interest., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

The red and far-red light photoreceptor phytochrome B (phyB) transmits light signals following cytosol-to-nuclear translocation to regulate transcriptional networks therein. This necessitates changes in protein-protein interactions of phyB in the cytosol, about which little is presently known. Via introduction of a nucleus-excluding G767R mutation into the dominant, constitutively active phyB Y276H (YHB) allele, we explore the functional consequences of expressing a cytosol-localized YHB G767R variant in transgenic Arabidopsis seedlings. We show that YHB G767R elicits selective constitutive photomorphogenic phenotypes in dark-grown phyABCDE null mutants, wild type and other phy-deficient genotypes. These responses include light-independent apical hook opening, cotyledon unfolding, seed germination and agravitropic hypocotyl growth with minimal suppression of hypocotyl elongation. Such phenotypes correlate with reduced PIF3 levels, which implicates cytosolic targeting of PIF3 turnover or PIF3 translational inhibition by YHB G767R . However, as expected for a cytoplasm-tethered phyB, YHB G767R elicits reduced light-mediated signaling activity compared with similarly expressed wild-type phyB in phyABCDE mutant backgrounds. YHB G767R also interferes with wild-type phyB light signaling, presumably by formation of cytosol-retained and/or otherwise inactivated heterodimers. Our results suggest that cytosolic interactions with PIFs play an important role in phyB signaling even under physiological conditions., (© 2024. The Author(s).)

Plants photoreceptors perceive changes in light quality and intensity and thereby regulate plant vegetative growth and reproductive development. By screening a γ irradiation-induced mutant library of the soybean ( Glycine max ) cultivar "Dongsheng 7", we identified Gmeny , a mutant with elongated nodes, yellowed leaves, decreased chlorophyll contents, altered photosynthetic performance, and early maturation. An analysis of bulked DNA and RNA data sampled from a population segregating for Gmeny , using the BVF-IGV pipeline established in our laboratory, identified a 10 bp deletion in the first exon of the candidate gene Glyma.02G304700 . The causative mutation was verified by a variation analysis of over 500 genes in the candidate gene region and an association analysis, performed using two populations segregating for Gmeny . Glyma.02G304700 ( GmHY2a ) is a homolog of AtHY2a in Arabidopsis thaliana , which encodes a PΦB synthase involved in the biosynthesis of phytochrome. A transcriptome analysis of Gmeny using the Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed changes in multiple functional pathways, including photosynthesis, gibberellic acid (GA) signaling, and flowering time, which may explain the observed mutant phenotypes. Further studies on the function of GmHY2a and its homologs will help us to understand its profound regulatory effects on photosynthesis, photomorphogenesis, and flowering time.

Rapid hypocotyl elongation allows buried seedlings to emerge, where light triggers de-etiolation and inhibits hypocotyl growth mainly by photoreceptors. Phosphorylation/dephosphorylation events regulate many aspects of plant development. Only recently we have begun to uncover the earliest phospho-signaling responders to light. Here, we reported a large-scale phosphoproteomic analysis and identified 20 proteins that changed their phosphorylation pattern following a 20 min light pulse compared to darkness. Microtubule-associated proteins were highly overrepresented in this group. Among them, we studied CIP7 (COP1-INTERACTING-PROTEIN 7), which presented microtubule (MT) localization in contrast to the previous description. An isoform of CIP7 phosphorylated at Serine 915 was detected in etiolated seedlings but was undetectable after a light pulse in the presence of photoreceptors, while CIP7 transcript expression decays with long light exposure. The short hypocotyl phenotype and rearrangement of MTs in etiolated cip7 mutants are complemented by CIP7-YFP and the phospho-mimetic CIP7 S915D -YFP, but not the phospho-null CIP7 S915A -YFP suggesting that the phosphorylated S 915 CIP7 isoform promotes hypocotyl elongation through MT reorganization in darkness. Our evidence on Serine 915 of CIP7 unveils phospho-regulation of MT-based processes during skotomorphogenic hypocotyl growth., (© 2024 Society for Experimental Biology and John Wiley & Sons Ltd.)

The Xishuangbanna (XIS) cucumber (Cucumis sativus var. xishuangbannanesis) is a semiwild variety that has many distinct agronomic traits. Here, long reads generated by Nanopore sequencing technology helped assembling a high-quality genome (contig N50 = 8.7 Mb) of landrace XIS49. A total of 10,036 structural/sequence variations (SVs) were identified when comparing with Chinese Long (CL), and known SVs controlling spines, tubercles, and carpel number were confirmed in XIS49 genome. Two QTLs of hypocotyl elongation under low light, SH3.1 and SH6.1, were fine-mapped using introgression lines (donor parent, XIS49; recurrent parent, CL). SH3.1 encodes a red-light receptor Phytochrome B (PhyB, CsaV3_3G015190). A ∼4 kb region with large deletion and highly divergent regions (HDRs) were identified in the promoter of the PhyB gene in XIS49. Loss of function of this PhyB caused a super-long hypocotyl phenotype. SH6.1 encodes a CCCH-type zinc finger protein FRIGIDA-ESSENTIAL LIKE (FEL, CsaV3_6G050300). FEL negatively regulated hypocotyl elongation but it was transcriptionally suppressed by long terminal repeats retrotransposon insertion in CL cucumber. Mechanistically, FEL physically binds to the promoter of CONSTITUTIVE PHOTOMORPHOGENIC 1a (COP1a), regulating the expression of COP1a and the downstream hypocotyl elongation. These above results demonstrate the genetic mechanism of cucumber hypocotyl elongation under low light., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Precise responses to changes in light quality are crucial for plant growth and development. For example, hypocotyls of shade-avoiding plants typically elongate under shade conditions. Although this typical shade-avoidance response (TSR) has been studied in Arabidopsis (Arabidopsis thaliana), the molecular mechanisms underlying shade tolerance are poorly understood. Here we report that B. napus (Brassica napus) seedlings exhibit dual shade responses. In addition to the TSR, B. napus seedlings also display an atypical shade response (ASR), with shorter hypocotyls upon perception of early-shade cues. Genome-wide selective sweep analysis indicated that ASR is associated with light and auxin signaling. Moreover, genetic studies demonstrated that phytochrome A (BnphyA) promotes ASR, whereas BnphyB inhibits it. During ASR, YUCCA8 expression is activated by early-shade cues, leading to increased auxin biosynthesis. This inhibits hypocotyl elongation, as young B. napus seedlings are highly sensitive to auxin. Notably, two non-canonical AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) repressor genes, BnIAA32 and BnIAA34, are expressed during this early stage. BnIAA32 and BnIAA34 inhibit hypocotyl elongation under shade conditions, and mutations in BnIAA32 and BnIAA34 suppress ASR. Collectively, our study demonstrates that the temporal expression of BnIAA32 and BnIAA34 determines the behavior of B. napus seedlings following shade-induced auxin biosynthesis., (© 2023 Institute of Botany, Chinese Academy of Sciences.)

Tobacco remains one of the most commercially important crops due to the parasympathomimetic alkaloid nicotine used in cigarettes. Most genes involved in nicotine biosynthesis are expressed in root tissues; however, their light-dependent regulation has not been studied. Here, we identified the ELONGATED HYPOCOTYL 5 homolog, NtHY5, from Nicotiana tabacum and demonstrated that NtHY5 could complement the Arabidopsis thaliana hy5 mutant at molecular, morphological and biochemical levels. We report the development of CRISPR/Cas9-based knockout mutant plants of tobacco, NtHY5 CR , and show down-regulation of the nicotine and phenylpropanoid pathway genes leading to a significant reduction in nicotine and flavonol content, whereas NtHY5 overexpression (NtHY5OX) plants show the opposite effect. Grafting experiments using wild-type, NtHY5 CR , and NtHY5OX indicated that NtHY5 moves from shoot-to-root to regulate nicotine biosynthesis in the root tissue. Shoot HY5, directly or through enhancing expression of the root HY5, promotes nicotine biosynthesis by binding to light-responsive G-boxes present in the NtPMT, NtQPT and NtODC promoters. We conclude that the mobility of HY5 from shoot-to-root regulates light-dependent nicotine biosynthesis. The CRISPR/Cas9-based mutants developed, in this study; with low nicotine accumulation in leaves could help people to overcome their nicotine addiction and the risk of death., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Legumes produce specialized root nodules that are distinct from lateral roots in morphology and function, with nodules intracellularly hosting nitrogen-fixing bacteria. We have previously shown that a lateral root program underpins nodule initiation, but there must be additional developmental regulators that confer nodule identity. Here, we show two members of the LIGHT-SENSITIVE SHORT HYPOCOTYL (LSH) transcription factor family, predominantly known to define shoot meristem complexity and organ boundaries, function as regulators of nodule organ identity. In parallel to the root initiation program, LSH1/LSH2 recruit a program into the root cortex that mediates the divergence into nodules, in particular with cell divisions in the mid-cortex. This includes regulation of auxin and cytokinin, promotion of NODULE ROOT1/2 and Nuclear Factor YA1, and suppression of the lateral root program. A principal outcome of LSH1/LSH2 function is the production of cells able to accommodate nitrogen-fixing bacteria, a key feature unique to nodules., Competing Interests: Declaration of interests Related to this work, we submitted a Patent Cooperation Treaty (PCT) Application (PCT/IB2023/055144) on May 18th, 2023 under the title “PROTEINS FOR REGULATION OF SYMBIOTIC NODULE ORGAN IDENTITY.”, (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Pectin methylesterases (PMEs) modify homogalacturonan's chemistry and play a key role in regulating primary cell wall mechanical properties. Here, we report on Arabidopsis AtPME2, which we found to be highly expressed during lateral root emergence and dark-grown hypocotyl elongation. We showed that dark-grown hypocotyl elongation was reduced in knock-out mutant lines as compared to the control. The latter was related to the decreased total PME activity as well as increased stiffness of the cell wall in the apical part of the hypocotyl. To relate phenotypic analyses to the biochemical specificity of the enzyme, we produced the mature active enzyme using heterologous expression in Pichia pastoris and characterized it through the use of a generic plant PME antiserum. AtPME2 is more active at neutral compared to acidic pH, on pectins with a degree of 55-70% methylesterification. We further showed that the mode of action of AtPME2 can vary according to pH, from high processivity (at pH8) to low processivity (at pH5), and relate these observations to the differences in electrostatic potential of the protein. Our study brings insights into how the pH-dependent regulation by PME activity could affect the pectin structure and associated cell wall mechanical properties., (© The Author(s) 2024. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The nuclear matrix is a nuclear compartment that has diverse functions in chromatin regulation and transcription. However, how this structure influences epigenetic modifications and gene expression in plants is largely unknown. In this study, we show that a nuclear matrix binding protein, AHL22, together with the two transcriptional repressors FRS7 and FRS12, regulates hypocotyl elongation by suppressing the expression of a group of genes known as SMALL AUXIN UP RNAs (SAURs) in Arabidopsis thaliana. The transcriptional repression of SAURs depends on their attachment to the nuclear matrix. The AHL22 complex not only brings these SAURs, which contain matrix attachment regions (MARs), to the nuclear matrix, but it also recruits the histone deacetylase HDA15 to the SAUR loci. This leads to the removal of H3 acetylation at the SAUR loci and the suppression of hypocotyl elongation. Taken together, our results indicate that MAR-binding proteins act as a hub for chromatin and epigenetic regulators. Moreover, we present a mechanism by which nuclear matrix attachment to chromatin regulates histone modifications, transcription, and hypocotyl elongation., (© 2024. The Author(s).)

TCP13 belongs to a subgroup of TCP transcription factors implicated in the shade avoidance syndrome (SAS), but its exact role remains unclear. Here, we show that TCP13 promotes the SAS-like response by enhancing hypocotyl elongation and suppressing flavonoid biosynthesis as a part of the incoherent feed-forward loop in light signaling. Shade is known to promote the SAS by activating PHYTOCHROME-INTERACTING FACTOR (PIF)-auxin signaling in plants, but we found no evidence in a transcriptome analysis that TCP13 activates PIF-auxin signaling. Instead, TCP13 mimics shade by activating the expression of a subset of shade-inducible and cell elongation-promoting SAUR genes including SAUR19, by direct targeting of their promoters. We also found that TCP13 and PIF4, a molecular proxy for shade, repress the expression of flavonoid biosynthetic genes by directly targeting both shared and distinct sets of biosynthetic gene promoters. Together, our results indicate that TCP13 promotes the SAS-like response by directly targeting a subset of shade-responsive genes without activating the PIF-auxin signaling pathway., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Hypocotyl elongation directly affects the seedling establishment and soil-breaking after germination. In soybean (Glycine max ), the molecular mechanisms regulating hypocotyl development remain largely elusive. To decipher the regulatory landscape, we conducted proteome and transcriptome analysis of soybean hypocotyl samples at different development stages. Our results showed that during hypocotyl development, many proteins were with extreme high translation efficiency (TE) and may act as regulators. These potential regulators include multiple peroxidases and cell wall reorganisation related enzymes. Peroxidases may produce ROS including H2 O2 . Interestingly, exogenous H2 O2 application promoted hypocotyl elongation, supporting peroxidases as regulators of hypocotyl development. However, a vast variety of proteins were shown to be with dramatically changed TE during hypocotyl development, including multiple phytochromes, plasma membrane intrinsic proteins (PIPs) and aspartic proteases. Their potential roles in hypocotyl development were confirmed by that ectopic expression of GmPHYA1 and GmPIP1-6 in Arabidopsis thaliana affected hypocotyl elongation. In addition, the promoters of these potential regulatory genes contain multiple light/gibberellin/auxin responsive elements, while the expression of some members in hypocotyls was significantly regulated by light and exogenous auxin/gibberellin. Overall, our results revealed multiple novel regulatory factors of soybean hypocotyl elongation. Further research on these regulators may lead to new approvals to improve soybean hypocotyl traits.

In plants, light direction is perceived by the phototropin photoreceptors, which trigger directional growth responses known as phototropism. The formation of a phototropin activation gradient across a photosensitive organ initiates this response. However, the optical tissue properties that functionally contribute to phototropism remain unclear. In this work, we show that intercellular air channels limit light transmittance through various organs in several species. Air channels enhance light scattering in Arabidopsis hypocotyls, thereby steepening the light gradient. This is required for an efficient phototropic response in Arabidopsis and Brassica. We identified an embryonically expressed ABC transporter required for the presence of air channels in seedlings and a structure surrounding them. Our work provides insights into intercellular air space development or maintenance and identifies a mechanism of directional light sensing in plants.

Hypocotyl length is a botanical trait that affects the cold tolerance of Brassica napus L. ( B. napus ). In this study, we constructed an F 2 segregating population using the cold-resistant short hypocotyl variety '16VHNTS158' and the cold-sensitive long hypocotyl variety 'Tianyou 2288' as the parents, and BSA-seq was employed to identify candidate genes for hypocotyl length in B. napus . The results of parental differences showed that the average hypocotyl lengths of '16VHNTS158' and 'Tianyou 2288' were 0.41 cm and 0.77 cm at the 5~6 leaf stage, respectively, after different low-temperature treatments, and '16VHNTS158' exhibited lower relative ion leakage rates compared to 'Tianyou 2288'. The contents of indole acetic acid (IAA), gibberellin (GA), and brassinosteroid (BR) in hypocotyls of '16VHNTS158' and 'Tianyou 2288' increased with decreasing temperatures, but the IAA and GA contents were significantly higher than those of 'Tianyou 2288', and the BR content was lower than that of 'Tianyou 2288'. The genetic analysis results indicate that the genetic model for hypocotyl length follows the 2MG-A model. By using SSR molecular markers, a QTL locus associated with hypocotyl length was identified on chromosome C04. The additive effect value of this locus was 0.025, and it accounted for 2.5% of the phenotypic variation. BSA-Seq further localized the major effect QTL locus on chromosome C04, associating it with 41 genomic regions. The total length of this region was 1.06 Mb. Within this region, a total of 20 non-synonymous mutation genes were identified between the parents, and 26 non-synonymous mutation genes were found within the pooled samples. In the reference genome of B. napus , this region was annotated with 24 candidate genes. These annotated genes are predominantly enriched in four pathways: DNA replication, nucleotide excision repair, plant hormone signal transduction, and mismatch repair. The findings of this study provide a theoretical basis for cloning genes related to hypocotyl length in winter rapeseed and their utilization in breeding.

Plant growth is coordinately controlled by various environmental and hormonal signals, of which light and gibberellin (GA) signals are two critical factors with opposite effects on hypocotyl elongation. Although interactions between the light and GA signaling pathways have been studied extensively, the detailed regulatory mechanism of their direct crosstalk in hypocotyl elongation remains to be fully clarified. Previously, we reported that ABA INSENSITIVE 4 (ABI4) controls hypocotyl elongation through its regulation of cell-elongation-related genes, but whether it is also involved in GA signaling to promote hypocotyl elongation is unknown. In this study, we show that promotion of hypocotyl elongation by GA is dependent on ABI4 activation. DELLAs interact directly with ABI4 and inhibit its DNA-binding activity. In turn, ABI4 combined with ELONGATED HYPOCOTYL 5 (HY5), a key positive factor in light signaling, feedback regulates the expression of the GA2ox GA catabolism genes and thus modulates GA levels. Taken together, our results suggest that the DELLA-ABI4-HY5 module may serve as a molecular link that integrates GA and light signals to control hypocotyl elongation., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Hypocotyl length is a critical determinant for the efficiency of mechanical harvesting in pakchoi production, but the knowledge on the molecular regulation of hypocotyl growth is very limited. Here, we report a spontaneous mutant of pakchoi, lhy7.1 , and identified its characteristics. We found that it has an elongated hypocotyl phenotype compared to the wild type caused by the longitudinal growth of hypocotyl cells. Different light quality treatments, transcriptome, and proteomic analyses were performed to reveal the molecular mechanisms of hypocotyl elongation. The data showed that the hypocotyl length of lhy7.1 was significantly longer than that of WT under red, blue, and white lights but there was no significant difference under dark conditions. Furthermore, we used transcriptome and label-free proteome analyses to investigate differences in gene and protein expression levels between lhy7.1 and WT. At the transcript level, 4568 differentially expressed genes (DEGs) were identified, which were mainly enriched in "plant hormone signal transduction", "photosynthesis", "photosynthesis-antenna proteins", and "carbon fixation in photosynthetic organisms" pathways. At the protein level, 1007 differentially expressed proteins (DEPs) were identified and were mainly enriched in photosynthesis-related pathways. The comprehensive transcriptome and proteome analyses revealed a regulatory network of hypocotyl elongation involving plant hormone signal transduction and photosynthesis-related pathways. The findings of this study help elucidate the regulatory mechanisms of hypocotyl elongation in lhy7.1 .

Reductions in red to far-red ratio (R:FR) provide plants with an unambiguous signal of vegetational shade and are monitored by phytochrome photoreceptors. Plants integrate this information with other environmental cues to determine the proximity and density of encroaching vegetation. Shade-sensitive species respond to reductions in R:FR by initiating a suite of developmental adaptations termed shade avoidance. These include the elongation of stems to facilitate light foraging. Hypocotyl elongation is driven by increased auxin biosynthesis promoted by PHYTOCHROME INTERACTING FACTORs (PIF) 4, 5 and 7. UV-B perceived by the UV RESISTANCE LOCUS 8 (UVR8) photoreceptor rapidly inhibits shade avoidance, in part by suppressing PIF4/5 transcript accumulation and destabilising PIF4/5 protein. Here, we show that longer-term inhibition of shade avoidance is sustained by ELONGATED HYPOCOTYL 5 (HY5) and HY5 HOMOLOGUE (HYH), which regulate transcriptional reprogramming of genes involved in hormone signalling and cell wall modification. HY5 and HYH are elevated in UV-B and suppress the expression of XYLOGLUCAN ENDOTRANSGLUCOSYLASE/HYDROLASE (XTH) genes involved in cell wall loosening. They additionally increase expression GA2-OXIDASE1 (GA2ox1) and GA2ox2, encoding gibberellin catabolism enzymes that act redundantly to stabilise the PIF-inhibiting DELLA proteins. UVR8 therefore regulates temporally distinct signalling pathways to first rapidly inhibit and subsequently maintain suppression of shade avoidance following UV-B exposure., (© 2023 The Authors. The Plant Journal published by Society for Experimental Biology and John Wiley & Sons Ltd.)

Amaranth plants contain abundant betalains and flavonoids. Anthocyanins are important flavonoids; however, they cannot coexist in the same plant with betalains. Blue light influences metabolite synthesis and hypocotyl elongation; accordingly, analyses of its effects on betalain and flavonoid biosynthesis in Amaranthus tricolor may provide insight into the distribution of these plant pigments. We analyzed the betalain and flavonoid content and transcriptome profiles in amaranth hypocotyls under blue light and dark conditions. Furthermore, we analyzed the expression patterns of key genes related to betalains and flavonoids. Amaranth hypocotyls were shorter and redder and showed higher betalain and flavonoid content under blue light than in dark conditions. Key genes involved in the synthesis of betalains and flavonoids were upregulated under blue light. The gene encoding DELLA was also upregulated. These results suggest that blue light favors the synthesis of both betalains and flavonoids via the suppression of bioactive gibberellin and the promotion of DELLA protein accumulation, which also suppresses hypocotyl elongation. The metabolite profiles differed between plants under blue light and dark conditions. These findings improve our understanding of the environmental cues and molecular mechanisms underlying pigment variation in Amaranthus .

Fusarium wilt of Luffa , caused by Fusarium oxysporum f. sp. luffae , causes great losses in Luffa plants worldwide. In this study, 45 accessions of Luffa germplasm were used to determine their resistance to F. oxysporum f. sp. luffae isolates (FOLUST, FOLUSC, Fomh16, and Fol114) in two independent trials. In the first trial, only FOLUST was used to preliminarily identify resistant accessions. Nine accessions of Luffa acutangula and five of L. aegyptiaca were resistant to the FOLUST isolate. In the second trial, the other three isolates were then used to reevaluate the 14 resistant accessions. The results indicated that the 14 accessions were resistant to FOLUSC but exhibited variable resistance to the Fomh16 and Fol114 isolates. Eight accessions of L. acutangula and one accession of L. aegyptiaca were resistant to Fol114. Seven accessions of L. acutangula and one accession of L. aegyptiaca were resistant to Fomh16. Despite the lack of any symptoms, the F. oxysporum f. sp. luffae isolates were recovered from the hypocotyls of all resistant accessions at 28 days postinoculation, except for isolates FOLUSC and FOLUST on one accession (LA140). A high percentage (87.5%) of accessions collected from Bangladesh were identified as resistant, highlighting the effect of local adaptation on resistance. These results provide potentially valuable genetic resources for breeding programs to develop new varieties or rootstocks that could be beneficial for controlling soilborne diseases in different cucurbit crops and further investigating the mechanisms of resistance to F. oxysporum f. sp. luffae in Luffa plants., Competing Interests: The author(s) declare no conflict of interest.

Abiotic stress, such as drought, osmotic, and salinity stresses, seriously affects plant growth and crop production. Studying stress-resistant genes that enhance plant stress tolerance is an efficient way to facilitate the breeding of crop species with high stress tolerance. In this study, we reported that the core circadian clock component, the LATE ELONGATED HYPOCOTYL ( LHY ) orthologue MtLHY , plays a positive role in salt stress response in Medicago truncatula . The expression of MtLHY was induced by salt stress, and loss-of-function mutants of MtLHY were shown to be hypersensitive to salt treatment. However, overexpression of MtLHY improved salt stress tolerance through a higher accumulation of flavonoids. Consistently, exogenous flavonol application improved the salt stress tolerance in M. truncatula . Additionally, MtLHY was identified as a transcriptional activator of the flavonol synthase gene, MtFLS . Our findings revealed that MtLHY confers plant salt stress tolerance, at least by modulating the flavonoid biosynthesis pathway, which provides insight into salt stress tolerance that links the circadian clock with flavonoid biosynthesis.

Integration of light and phytohormones is essential for plant growth and development. FAR-RED INSENSITIVE 219 (FIN219)/JASMONATE RESISTANT 1 (JAR1) participates in phytochrome A (phyA)-mediated far-red (FR) light signaling in Arabidopsis and is a jasmonate (JA)-conjugating enzyme for the generation of an active JA-isoleucine. Accumulating evidence indicates that FR and JA signaling integrate with each other. However, the molecular mechanisms underlying their interaction remain largely unknown. Here, the phyA mutant was hypersensitive to JA. The double mutant fin219-2phyA-211 showed a synergistic effect on seedling development under FR light. Further evidence revealed that FIN219 and phyA antagonized with each other in a mutually functional demand to modulate hypocotyl elongation and expression of light- and JA-responsive genes. Moreover, FIN219 interacted with phyA under prolonged FR light, and MeJA could enhance their interaction with CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) in the dark and FR light. FIN219 and phyA interaction occurred mainly in the cytoplasm, and they regulated their mutual subcellular localization under FR light. Surprisingly, the fin219-2 mutant abolished the formation of phyA nuclear bodies under FR light. Overall, these data identified a vital mechanism of phyA-FIN219-COP1 association in response to FR light, and MeJA may allow the photoactivated phyA to trigger photomorphogenic responses., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Jiang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

AT-hook motif nuclear localization (AHL) proteins play essential roles in various plant biological processes. Yet, a comprehensive understanding of AHL transcription factors in walnut ( Juglans regia L.) is missing. In this study, 37 AHL gene family members were first identified in the walnut genome. Based on the evolutionary analysis, JrAHL genes were grouped into two clades, and their expansion may occur due to segmental duplication. The stress-responsive nature and driving of developmental activities of JrAHL genes were revealed by cis -acting elements and transcriptomic data, respectively. Tissue-specific expression analysis showed that JrAHLs had a profound transcription in flower and shoot tip, JrAHL2 in particular. Subcellular localization showed that JrAHL2 is anchored to the nucleus. Overexpression of JrAHL2 in Arabidopsis adversely affected hypocotyl elongation and delayed flowering. Our study, for the first time, presented a detailed analysis of JrAHL genes in walnut and provided theoretical knowledge for future genetic breeding programs.

Phytochromes are red light and far-red light sensitive, plant-specific light receptors that allow plants to orient themselves in space and time. Tomato (Solanum lycopersicum) contains a small family of five phytochrome genes, for which to date stable knockout mutants are only available for three of them. Using CRISPR technology, we created multiple alleles of SlPHYTOCHROME F (phyF) mutants to determine the function of this understudied phytochrome. We report that SlphyF acts as a red/far-red light reversible low fluence sensor, likely through the formation of heterodimers with SlphyB1 and SlphyB2. During photomorphogenesis, phyF functions additively with phyB1 and phyB2. Our data further suggest that phyB2 requires the presence of either phyB1 or phyF during seedling de-etiolation in red light, probably via heterodimerization, while phyB1 homodimers are required and sufficient to suppress hypocotyl elongation in red light. During the end-of-day far-red response, phyF works additively with phyB1 and phyB2. In addition, phyF plays a redundant role with phyB1 in photoperiod detection and acts additively with phyA in root patterning. Taken together, our results demonstrate various roles for SlphyF during seedling establishment, sometimes acting additively, other times acting redundantly with the other phytochromes in tomato., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2023. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Key Message: Our findings indicated that the SlERF.J2-IAA23 module integrates hormonal signals to regulate hypocotyl elongation and plant height in tomato. Light and phytohormones can synergistically regulate photomorphogenesis-related hypocotyl elongation and plant height in tomato. AP2/ERF family genes have been extensively demonstrated to play a role in light signaling and various hormones. In this study, we identified a novel AP2/ERF family gene in tomato, SlERF.J2. Overexpression of SlERF.J2 inhibits hypocotyl elongation and plant height. However, the plant height in the slerf.j2 ko knockout mutant was not significantly changed compared with the WT. we found that hypocotyl cell elongation and plant height were regulated by a network involving light, auxin and gibberellin signaling, which is mediated by regulatory relationship between SlERF.J2 and IAA23. SlERF.J2 protein could bind to IAA23 promoter and inhibit its expression. In addition, light-dark alternation can activate the transcription of SlERF.J2 and promote the function of SlERF.J2 in photomorphogenesis. Our findings indicated that the SlERF.J2-IAA23 module integrates hormonal signals to regulate hypocotyl elongation and plant height in tomato., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Background: Plants have evolved to adapt to the ever-changing environments through various morphological changes. An organism anticipates and responds to changes in its environment via the circadian clock, an endogenous oscillator lasting approximately 24 h. The circadian clock regulates various physiological processes, such as hypocotyl elongation in Arabidopsis thaliana. Phytochrome interacting factor 4 (PIF4), a member of the bHLH protein family, plays a vital hub role in light signaling pathways and temperature-mediated growth response mechanisms. PIF4 is controlled by the circadian clock and interacts with several factors. However, the components that regulate PIF4 transcription and activity are not clearly understood., Methods and Results: Here, we showed that the Arabidopsis thaliana GATA25 (AtGATA25) transcription factor plays a fundamental role in promoting hypocotyl elongation by positively regulating the expression of PIF4. This was confirmed to in the loss-of-function mutant of AtGATA25 via CRISPR/Cas9-mediated gene editing, which inhibits hypocotyl elongation and decreases the expression of PIF4. In contrast, the overexpression of AtGATA25 in transgenic plants resulted in increased expression of PIF4 and enhanced hypocotyl elongation. To better understand AtGATA25-mediated PIF4 transcriptional regulation, we analyzed the promoter region of the target gene PIF4 and characterized the role of GATA25 through transcriptional activation analysis., Conclusion: Our findings suggest a novel role of the AtGATA25 transcription factor in hypocotyl elongation., (© 2022. The Author(s).)

Some of the hormone crosstalk and transcription factors (TFs) involved in wound-induced organ regeneration have been extensively studied in the model plant Arabidopsis thaliana . In previous work, we established Solanum lycopersicum "Micro-Tom" explants without the addition of exogenous hormones as a model to investigate wound-induced de novo organ formation. The current working model indicates that cell reprogramming and founder cell activation requires spatial and temporal regulation of auxin-to-cytokinin (CK) gradients in the apical and basal regions of the hypocotyl combined with extensive metabolic reprogramming of some cells in the apical region. In this work, we extended our transcriptomic analysis to identify some of the gene regulatory networks involved in wound-induced organ regeneration in tomato. Our results highlight a functional conservation of key TF modules whose function is conserved during de novo organ formation in plants, which will serve as a valuable resource for future studies.

The effects of the quality of light on the content of phytochrome interacting factors (PIFs) such as PIF3, PIF4 and PIF5, as well as the expression of various light-dependent microRNAs, in adult Arabidopsis thaliana pif mutant plants ( pif4 , pif5 , pif3pif5 , pif4pif5 , pif3pif4pif5 ) were studied. We demonstrate that under blue light, the pif4 mutant had maximal expression of most of the studied microRNAs (miR163, miR319, miR398, miR408, miR833) when the PIF4 protein in plants was reduced. This finding indicates that the PIF4 protein is involved in the downregulation of this group of microRNAs. This assumption is additionally confirmed by the fact that under the RL spectrum in pif5 mutants, practically the same miRNAs decrease expression against the background of an increase in the amount of PIF4 protein. Unlike the WT and other mutants, the pif4 mutant responded to the BL spectrum not only by activating the expression of light-dependent miRNAs, but also by a significant increase in the expression of transcription factors and key light signalling genes. These molecular reactions do not affect the activity of photosynthesis but may be involved in the formation of a light quality-dependent phenotype.

Plant growth ultimately depends on fixed carbon, thus the available light for photosynthesis. Due to canopy light absorption properties, vegetative shade combines low blue (LB) light and a low red to far-red ratio (LRFR). In shade-avoiding plants, these two conditions independently trigger growth adaptations to enhance light access. However, how these conditions, differing in light quality and quantity, similarly promote hypocotyl growth remains unknown. Using RNA sequencing we show that these two features of shade trigger different transcriptional reprogramming. LB induces starvation responses, suggesting a switch to a catabolic state. Accordingly, LB promotes autophagy. In contrast, LRFR induced anabolism including expression of sterol biosynthesis genes in hypocotyls in a manner dependent on PHYTOCHROME-INTERACTING FACTORs (PIFs). Genetic analyses show that the combination of sterol biosynthesis and autophagy is essential for hypocotyl growth promotion in vegetative shade. We propose that vegetative shade enhances hypocotyl growth by combining autophagy-mediated recycling and promotion of specific lipid biosynthetic processes., (© 2022. The Author(s).)

Key Message: The causal gene, CaHY5 of a chemical induced green-hypocotyl mutant was identified by molecular mapping. CaHY5 regulates anthocyanin accumulation by directly binding to the promoter of genes in anthocyanin pathway. Morphological markers at seedling stage are useful indicators for F 1 hybrid seeds screening. Pepper is a worldwide vegetable with diverse uses, and F 1 hybrids are popular in the pepper industry. Hypocotyl color is a useful marker to identify F 1 hybrid seeds. However, most pepper accessions have purple hypocotyl caused by anthocyanin accumulation, while green hypocotyl pepper accessions are rare. In this study, we identified a green hypocotyl mutant (e1898) from a pepper ethylmethanesulfonate (EMS) mutant library. By combining bulked segregant RNA-seq (BSR), genome resequencing and recombinant analysis, it was found that CaHY5 is the causal gene of this mutant. Virus-induced gene silencing (VIGS) of CaHY5 resulted in the decrease of anthocyanin accumulation in pepper hypocotyls. RNA-seq data showed that many genes related to anthocyanin biosynthesis and transport decreased significantly in the mutant. Yeast one-hybrid (Y1H) assays showed that CaHY5 can bind to the promoter of CaF3H, CaF3'5'H, CaDFR, CaANS and CaGST, which are important genes in anthocyanin biosynthesis or transport. Our results indicate that CaHY5 directly regulates anthocyanin biosynthesis and transport, thus governing anthocyanin accumulation in pepper hypocotyl. The mutant and gene identified in this work shall be valuable in the purity control of hybrid pepper seeds., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

UV-B as a component of natural solar radiation can induce damage and morphological development in plants. The UV-B response from germination and early development in seedlings is still largely unknown, with most studies focused on older, light-exposed seedlings. We used fluence response curves measuring hypocotyl length after UV-B exposure coupled with RNA-seq and sRNA-seq evaluation of the early seedling response in the model organism Arabidopsis thaliana. We identified miR5642 as a potential novel key regulator of UV-B responses. miR5642 is a noncanonical miRNA predicted to target previously known and unknown components involved in hypocotyl growth inhibition. These include (i) SMAX1, a signal transmitter for seedling germination and growth; (ii) ZAT1, an uncharacterized transcription factor; and (iii) membrane pores and transporters (VHA-E1, VHA-E3, EPSIN-LIKE and PIP1.4) implicated in cell elongation. In addition, HY5 and HYH, two homologous and redundant transcription factors involved in seedling photomorphogenesis, may interact with these newly identified components. Interestingly, UV-B-induced DNA photodimer formation seems to be the direct trigger leading to inhibition of hypocotyl growth through a combination of cellular decisions including cell cycle arrest, reduced endoreduplication and reduced cell elongation, and this inhibition appears to be modulated by miR5642 target genes., (© 2021 American Society for Photobiology.)

Cryptochrome 2 (CRY2) perceives blue/UV-A light and regulates photomorphogenesis in plants. However, besides Arabidopsis, CRY2 has been functionally characterized only in native species of japonica rice and tomato. In the present study, the BnCRY2a, generating a relatively longer cDNA and harboring an intron in its 5'UTR, has been characterized in detail. Western blot analysis revealed that BnCRY2a is light labile and degraded rapidly by 26S proteasome when seedlings are irradiated with blue light. For functional analysis, BnCRY2a was over-expressed in Brassica juncea, a related species more amenable to transformation. The BnCRY2a over-expression (BnCRY2a OE ) transgenics developed short hypocotyl and expanded cotyledons, accumulated more anthocyanin in light-grown seedlings, and displayed early flowering on maturity. Early flowering in BnCRY2a OE transgenics was coupled with the up-regulation of many flowering-related genes such as FT. The present study also highlights the differential light sensitivity of cry1 and cry2 in controlling hypocotyl elongation growth in Brassica. BnCRY2a OE seedlings developed much shorter hypocotyl under the low-intensity of blue light, while BnCRY1 OE seedling hypocotyls were shorter under the high-intensity blue light, compared to untransformed seedlings., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

Melatonin (N-acetyl-5-methoxytryptamine) biosynthesis in plants is induced by darkness and high-intensity light; however, the underlying transcriptional mechanisms and upstream signalling pathways are unknown. We identified a dark-induced and highly expressed melatonin synthetase in Arabidopsis thaliana, AtSNAT6, encoding serotonin N-acetyltransferase. We assessed melatonin content and AtSNAT6 expression in mutants lacking key regulators of light/dark signalling. AtCOP1 (CONSTITUTIVE PHOTOMORPHOGENIC 1) and AtHY5 (ELONGATED HYPOCOTYL 5), which control light/dark transition and photomorphogenesis, promoted and suppressed melatonin biosynthesis, respectively. Using EMSA and ChIP-qPCR analysis, we showed that AtHY5 inhibits AtSNAT6 expression directly. An analysis of melatonin content in snat6 hy5 double mutant and AtHY5+AtSNAT6-overexpressing plants confirmed the regulatory function of AtHY5 and AtSNAT6 in melatonin biosynthesis. Exogenous melatonin further inhibited cotyledon opening in hy5 mutant and AtSNAT6-overexpressing seedlings, but partially reversed the promotion of cotyledon opening in AtHY5-overexpressing seedlings and snat6. Additionally, CRISPR/Cas9-mediated mutation of AtSNAT6 increased cotyledon opening in hy5 mutant, and overexpression of AtSNAT6 decreased cotyledon opening in AtHY5-overexpressing seedlings via changing melatonin biosynthesis, confirming that AtHY5 decreased melatonin-mediated inhibition of cotyledon opening. Our data provide new insights into the regulation of melatonin biosynthesis and its function in cotyledon opening., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Many plants, including Arabidopsis (Arabidopsis thaliana), accumulate starch in the daytime and remobilize it to support maintenance and growth at night. Starch accumulation is increased when carbon is in short supply, for example, in short photoperiods. Mobilization is paced to exhaust starch around dawn, as anticipated by the circadian clock. This diel pattern of turnover is largely robust against loss of day, dawn, dusk, or evening clock components. Here, we investigated diel starch turnover in the triple circadian clock mutant lhy cca1 elf3, which lacks the LATE ELONGATED HYPOCOTYL and the CIRCADIAN CLOCK-ASSOCIATED1 (CCA1) dawn components and the EARLY FLOWERING3 (ELF3) evening components of the circadian clock. The diel oscillations of transcripts for the remaining clock components and related genes like REVEILLE and PHYTOCHROME-INTERACING FACTOR family members exhibited attenuated amplitudes and altered peak time, weakened dawn dominance, and decreased robustness against changes in the external light-dark cycle. The triple mutant was unable to increase starch accumulation in short photoperiods. However, it was still able to pace starch mobilization to around dawn in different photoperiods and growth irradiances and to around 24 h after the previous dawn in T17 and T28 cycles. The triple mutant was able to slow down starch mobilization after a sudden low-light day or a sudden early dusk, although in the latter case it did not fully compensate for the lengthened night. Overall, there was a slight trend to less linear mobilization of starch. Thus, starch mobilization can be paced rather robustly to dawn despite a major disruption of the transcriptional clock. It is proposed that temporal information can be delivered from clock components or a semi-autonomous oscillator., (© The Author(s) 2022. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Adventitious roots (ARs) are an important type of plant root and display high phenotypic plasticity in response to different environmental stimuli. It is known that photoreceptors inhibit darkness-induced hypocotyl adventitious root (HAR) formation by directly stabilizing Aux/IAA proteins. In this study, we further report that phytochrome-interacting factors (PIFs) plays a central role in HAR initiation by simultaneously inducing the expression of genes involved in auxin biosynthesis, auxin transport and the transcriptional control of root primordium initiation. We found that, on the basis of their activity downstream of phytochrome, PIFs are required for darkness-induced HAR formation. Specifically, PIFs directly bind to the promoters of some genes involved in root formation, including auxin biosynthesis genes YUCCA2 (YUC2) and YUC6, the auxin influx carrier genes AUX1 and LAX3, and the transcription factors WOX5/7 and LBD16/29, to activate their expression. These findings reveal a previously uncharacterized transcriptional regulatory network underlying HAR formation., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2022. Published by The Company of Biologists Ltd.)

Photomorphogenic responses of etiolated seedlings include the inhibition of hypocotyl elongation and opening of the apical hook. In addition, dark-grown seedlings respond to light by the formation of adventitious roots (AR) on the hypocotyl. How light signaling controls adventitious rooting is less well understood. Hereto, we analyzed adventitious rooting under different light conditions in wild type and photomorphogenesis mutants in Arabidopsis thaliana . Etiolation was not essential for AR formation but raised the competence to form AR under white and blue light. The blue light receptors CRY1 and PHOT1/PHOT2 are key elements contributing to the induction of AR formation in response to light. Furthermore, etiolation-controlled competence for AR formation depended on the COP9 signalosome, E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC (COP1), the COP1 interacting SUPPRESSOR OF PHYA-105 (SPA) kinase family members (SPA1,2 and 3) and Phytochrome-Interacting Factors (PIF). In contrast, ELONGATED HYPOCOTYL5 (HY5), suppressed AR formation. These findings provide a genetic framework that explains the high and low AR competence of Arabidopsis thaliana hypocotyls that were treated with dark, and light, respectively. We propose that light-induced auxin signal dissipation generates a transient auxin maximum that explains AR induction by a dark to light switch.