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Rho/Rac of plant (ROP) GTPases are plant-specific proteins that function as molecular switches, activated by guanine nucleotide exchange factors (GEFs) and inactivated by GTPase-activating proteins (GAPs). The bryophyte Marchantia polymorpha contains single copies of ROP (MpROP), GEFs [ROPGEF and SPIKE (SPK)] and GAPs [ROPGAP and ROP ENHANCER (REN)]. MpROP regulates the development of various tissues and organs, such as rhizoids, gemmae and air chambers. The ROPGEF KARAPPO (MpKAR) is essential for gemma initiation, but the functions of other ROP regulatory factors are less understood. This study focused on two GAPs: MpROPGAP and MpREN. Mpren single mutants showed defects in thallus growth, rhizoid tip growth, gemma development, and air-chamber formation, whereas Mpropgap mutants showed no visible abnormalities. However, Mpropgap Mpren double mutants had more severe phenotypes than the Mpren single mutants, suggesting backup roles of MpROPGAP in processes involving MpREN. Overexpression of MpROPGAP and MpREN resulted in similar gametophyte defects, highlighting the importance of MpROP activation/inactivation cycling (or balancing). Thus, MpREN predominantly, and MpROPGAP as a backup, regulate gametophyte development, likely by controlling MpROP activation in M. polymorpha., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

De novo shoot apical meristem (SAM) organogenesis during regeneration in tissue culture has been investigated for several decades, but the precise mechanisms governing early-stage cell fate specification remain elusive. In contrast to SAM establishment during embryogenesis, in vitro SAM formation occurs without positional cues and is characterized by autonomous initiation of cellular patterning. Here, we report on the initial stages of SAM organogenesis and on the molecular mechanisms that orchestrate gene patterning to establish SAM homeostasis. We found that SAM organogenesis in tobacco calli starts with protuberance formation followed by the formation of an intact L1 layer covering the nascent protuberance. We also exposed a complex interdependent relationship between L1 and WUS expression and revealed that any disruption in this interplay compromises shoot formation. Silencing WUS in nascent protuberances prevented L1 formation and caused the disorganization of the outer cell layers exhibiting both anticlinal and periclinal divisions, suggesting WUS plays a critical role in the proper establishment and organization of L1 during SAM organogenesis. We further discovered that silencing TONNEAU1 prevents the exclusive occurrence of anticlinal divisions in the outermost layer of the protuberances and suppresses the acquisition of L1 cellular identity and L1 formation, ultimately impeding SAM formation and regeneration. This study provides a novel molecular framework for the characterization of a WUS/L1 interplay that mediates SAM formation during regeneration., (© 2024 Society for Experimental Biology and John Wiley & Sons Ltd.)

The lateral root (LR) is an essential component of the plant root system, performing important functions for nutrient and water uptake in plants and playing a pivotal role in cereal crop productivity. Nitrate (NO 3 - ) is an essential nutrient for plants. In this study, wheat plants were grown in 1/2 strength Hoagland's solution containing 5 mM NO 3 - (check; CK), 0.1 mM NO 3 - (low NO 3 - ; LN), or 0.1 mM NO 3 - plus 60 mg/L 2,3,5-triiodobenzoic acid (TIBA) (LNT). The results showed that LN increased the LR number significantly at 48 h after treatment compared with CK, while not increasing the root biomass, and LNT significantly decreased the LR number and root biomass. The transcriptomic analysis showed that LN induced the expression of genes related to root IAA synthesis and transport and cell wall remodeling, and it was suppressed in the LNT conditions. A physiological assay revealed that the LN conditions increased the activity of IAA biosynthesis-related enzymes, the concentrations of tryptophan and IAA, and the activity of cell wall remodeling enzymes in the roots, whereas the content of polysaccharides in the LRP cell wall was significantly decreased compared with the control. Fourier-transform infrared spectroscopy and atomic microscopy revealed that the content of cell wall polysaccharides decreased and the cell wall elasticity of LR primordia (LRP) increased under the LN conditions. The effects of LN on IAA synthesis and polar transport, cell wall remodeling, and LR development were abolished when TIBA was applied. Our findings indicate that NO 3 - starvation may improve auxin homeostasis and the biological properties of the LRP cell wall and thus promote LR initiation, while TIBA addition dampens the effects of LN on auxin signaling, gene expression, physiological processes, and the root architecture.

Bamboo with its remarkable growth rate and economic significance, offers an ideal system to investigate the molecular basis of organogenesis in rapidly growing plants, particular in monocots, where gene regulatory networks governing the maintenance and differentiation of shoot apical and intercalary meristems remain a subject of controversy. We employed both spatial and single-nucleus transcriptome sequencing on 10× platform to precisely dissect the gene functions in various tissues and early developmental stages of bamboo shoots. Our comprehensive analysis reveals distinct cell trajectories during shoot development, uncovering critical genes and pathways involved in procambium differentiation, intercalary meristem formation, and vascular tissue development. Spatial and temporal expression patterns of key regulatory genes, particularly those related to hormone signaling and lipid metabolism, strongly support the hypothesis that intercalary meristem origin from surrounded parenchyma cells. Specific gene expressions in intercalary meristem exhibit regular and dispersed distribution pattern, offering clues for understanding the intricate molecular mechanisms that drive the rapid growth of bamboo shoots. The single-nucleus and spatial transcriptome analysis reveal a comprehensive landscape of gene activity, enhancing the understanding of the molecular architecture of organogenesis and providing valuable resources for future genomic and genetic studies relying on identities of specific cell types., (© 2024 The Author(s). New Phytologist © 2024 New Phytologist Foundation.)

Legumes acquire nitrogen-fixing ability by forming root nodules. Transferring this capability to more crops could reduce our reliance on nitrogen fertilizers, thereby decreasing environmental pollution and agricultural production costs. Nodule organogenesis is complex, and a comprehensive transcriptomic atlas is crucial for understanding the underlying molecular events. Here, we utilized spatial transcriptomics to investigate the development of nodules in the model legume, Lotus japonicus. Our investigation has identified the developmental trajectories of two critical regions within the nodule: the infection zone and peripheral tissues. We reveal the underlying biological processes and provide gene sets to achieve symbiosis and material exchange, two essential aspects of nodulation. Among the candidate regulatory genes, we illustrate that LjNLP3, a transcription factor belonging to the NIN-LIKE PROTEIN family, orchestrates the transition of nodules from the differentiation to maturation. In summary, our research advances our understanding of nodule organogenesis and provides valuable data for developing symbiotic nitrogen-fixing crops., (© 2024. The Author(s).)

Plants have an astonishing ability to regenerate new organs after wounding. Here, we report that the wound-inducible transcription factor ENHANCER OF SHOOT REGENERATION1 (ESR1) has a dual mode of action in activating ANTHRANILATE SYNTHASE ALPHA SUBUNIT1 (ASA1) expression to ensure auxin-dependent de novo root organogenesis locally at wound sites of Arabidopsis (Arabidopsis thaliana) leaf explants. In the first mode, ESR1 interacts with HISTONE DEACETYLASE6 (HDA6), and the ESR1-HDA6 complex directly binds to the JASMONATE-ZIM DOMAIN5 (JAZ5) locus, inhibiting JAZ5 expression through histone H3 deacetylation. As JAZ5 interferes with the action of ETHYLENE RESPONSE FACTOR109 (ERF109), the transcriptional repression of JAZ5 at the wound site allows ERF109 to activate ASA1 expression. In the second mode, the ESR1 transcriptional activator directly binds to the ASA1 promoter to enhance its expression. Overall, our findings indicate that the dual biochemical function of ESR1, which specifically occurs near wound sites of leaf explants, maximizes local auxin biosynthesis and de novo root organogenesis in Arabidopsis., 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.)

Endoreduplication is the major source of somatic endopolyploidy in higher plants, and leads to variation in cell ploidy levels due to iterative rounds of DNA synthesis in the absence of mitosis. Despite its ubiquitous occurrence in many plant organs, tissues, and cells, the physiological meaning of endoreduplication is not fully understood, although several roles during plant development have been proposed, mostly related to cell growth, differentiation, and specialization via transcriptional and metabolic reprogramming. Here, we review recent advances in our knowledge of the molecular mechanisms and cellular characteristics of endoreduplicated cells, and provide an overview of the multi-scale effects of endoreduplication on supporting growth in plant development. In addition, the effects of endoreduplication in fruit development are discussed, since it is highly prominent during fruit organogenesis where it acts as a morphogenetic factor supporting rapid fruit growth, as illustrated by case of the model fleshy fruit, tomato (Solanum lycopersicum)., (© 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.)

Wounded plant cells can form callus to seal the wound site. Alternatively, wounding can cause adventitious organogenesis or somatic embryogenesis. These distinct developmental pathways require specific cell fate decisions. Here, we identify GhTCE1, a basic helix-loop-helix family transcription factor, and its interacting partners as a central regulatory module of early cell fate transition during in vitro dedifferentiation of cotton (Gossypium hirsutum). RNAi- or CRISPR/Cas9-mediated loss of GhTCE1 function resulted in excessive accumulation of reactive oxygen species (ROS), arrested callus cell elongation, and increased adventitious organogenesis. In contrast, GhTCE1-overexpressing tissues underwent callus cell growth, but organogenesis was repressed. Transcriptome analysis revealed that several pathways depend on proper regulation of GhTCE1 expression, including lipid transfer pathway components, ROS homeostasis, and cell expansion. GhTCE1 bound to the promoters of the target genes GhLTP2 and GhLTP3, activating their expression synergistically, and the heterodimer TCE1-TCEE1 enhances this activity. GhLTP2- and GhLTP3-deficient tissues accumulated ROS and had arrested callus cell elongation, which was restored by ROS scavengers. These results reveal a unique regulatory network involving ROS and lipid transfer proteins, which act as potential ROS scavengers. This network acts as a switch between unorganized callus growth and organized development during in vitro dedifferentiation of cotton cells., (© The Author(s) 2022. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Background: Reactive oxygen species (ROS) and calcium ions (Ca 2+ ) are representative signals of plant wound responses. Wounding triggers cell fate transition in detached plant tissues and induces de novo root organogenesis. While the hormonal regulation of root organogenesis has been widely studied, the role of early wound signals including ROS and Ca 2+ remains largely unknown., Results: We identified that ROS and Ca 2+ are required for de novo root organogenesis, but have different functions in Arabidopsis explants. The inhibition of the ROS and Ca 2+ signals delayed root development in detached leaves. Examination of the auxin signaling pathways indicated that ROS and Ca 2+ did not affect auxin biosynthesis and transport in explants. Additionally, the expression of key genes related to auxin signals during root organogenesis was not significantly affected by the inhibition of ROS and Ca 2+ signals. The addition of auxin partially restored the suppression of root development by the ROS inhibitor; however, auxin supplementation did not affect root organogenesis in Ca 2+ -depleted explants., Conclusions: Our results indicate that, while both ROS and Ca 2+ are key molecules, at least in part of the auxin signals acts downstream of ROS signaling, and Ca 2+ acts downstream of auxin during de novo root organogenesis in leaf explants., (© 2022. The Author(s).)

Arabidopsis (Arabidopsis thaliana) root hairs develop as long tubular extensions from the rootward pole of trichoblasts and exert polarized tip growth. The establishment and maintenance of root hair polarity is a complex process involving the local apical production of reactive oxygen species generated by A. thaliana nicotinamide adenine dinucleotide phosphate (NADPH) oxidase respiratory burst oxidase homolog protein C/ROOT HAIR-DEFECTIVE 2 (AtRBOHC/RHD2). Loss-of-function root hair defective 2 (rhd2) mutants have short root hairs that are unable to elongate by tip growth, and this phenotype is fully complemented by GREEN FLUORESCENT PROTEIN (GFP)-RHD2 expressed under the RHD2 promoter. However, the spatiotemporal mechanism of AtRBOHC/RHD2 subcellular redistribution and delivery to the plasma membrane (PM) during root hair initiation and tip growth are still unclear. Here, we used advanced microscopy for detailed qualitative and quantitative analysis of vesicular compartments containing GFP-RHD2 and characterization of their movements in developing bulges and growing root hairs. These compartments, identified by an independent molecular marker mCherry-VTI12 as the trans-Golgi network (TGN), deliver GFP-RHD2 to the apical PM domain, the extent of which corresponds with the stage of root hair formation. Movements of TGN/early endosomes, but not late endosomes, were affected in the bulging domains of the rhd2-1 mutant. Finally, we revealed that structural sterols might be involved in the accumulation, docking, and incorporation of TGN compartments containing GFP-RHD2 to the apical PM of root hairs. These results help in clarifying the mechanism of polarized AtRBOHC/RHD2 targeting, maintenance, and recycling at the apical PM domain, coordinated with different developmental stages of root hair initiation and growth., (© The Author(s) 2022. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Background: Bougainvillea is a popular ornamental plant with brilliant color and long flowering periods. It is widely distributed in the tropics and subtropics. The primary ornamental part of the plant is its colorful and unusual bracts, rich in the stable pigment betalain. The developmental mechanism of the bracts is not clear, and the pathway of betalain biosynthesis is well characterized in Bougainvillea., Results: At the whole-genome level, we found 23,469 protein-coding genes by assembling the RNA-Seq and Iso-Seq data of floral and leaf tissues. Genome evolution analysis revealed that Bougainvillea is related to spinach; the two diverged approximately 52.7 million years ago (MYA). Transcriptome analysis of floral organs revealed that flower development of Bougainvillea was regulated by the ABCE flower development genes; A-class, B-class, and E-class genes exhibited high expression levels in bracts. Eight key genes of the betalain biosynthetic pathway were identified by homologous alignment, all of which were upregulated concurrently with bract development and betalain accumulation during the bract initiation stage of development. We found 47 genes specifically expressed in stamens, including seven highly expressed genes belonging to the pentose and glucuronate interconversion pathways. BgSEP2b, BgSWEET11, and BgRD22 are hub genes and interacted with many transcription factors and genes in the carpel co-expression network., Conclusions: We assembled protein-coding genes of Bougainvilea, identified the floral development genes, and constructed the gene co-expression network of petal, stamens, and carpel. Our results provide fundamental information about the mechanism of flower development and pigment accumulation in Bougainvillea, and will facilitate breeding of cultivars with high ornamental value., (© 2022. The Author(s).)

The synthetic strigolactone (SL) analog, rac-GR24, has been instrumental in studying the role of SLs as well as karrikins because it activates the receptors DWARF14 (D14) and KARRIKIN INSENSITIVE 2 (KAI2) of their signaling pathways, respectively. Treatment with rac-GR24 modifies the root architecture at different levels, such as decreasing the lateral root density (LRD), while promoting root hair elongation or flavonol accumulation. Previously, we have shown that the flavonol biosynthesis is transcriptionally activated in the root by rac-GR24 treatment, but, thus far, the molecular players involved in that response have remained unknown. To get an in-depth insight into the changes that occur after the compound is perceived by the roots, we compared the root transcriptomes of the wild type and the more axillary growth2 (max2) mutant, affected in both SL and karrikin signaling pathways, with and without rac-GR24 treatment. Quantitative reverse transcription (qRT)-PCR, reporter line analysis and mutant phenotyping indicated that the flavonol response and the root hair elongation are controlled by the ELONGATED HYPOCOTYL 5 (HY5) and MYB12 transcription factors, but HY5, in contrast to MYB12, affects the LRD as well. Furthermore, we identified the transcription factors TARGET OF MONOPTEROS 5 (TMO5) and TMO5 LIKE1 as negative and the Mediator complex as positive regulators of the rac-GR24 effect on LRD. Altogether, hereby, we get closer toward understanding the molecular mechanisms that underlay the rac-GR24 responses in the root., (© The Author(s) 2021. 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.)

Highly efficient tissue repair is pivotal for surviving damage-associated stress. Plants generate callus upon injury to heal wound sites, yet regulatory mechanisms of tissue repair remain elusive. Here, we identified WUSCHEL-RELATED HOMEOBOX 13 (WOX13) as a key regulator of callus formation and organ adhesion in Arabidopsis (Arabidopsis thaliana). WOX13 belongs to an ancient subclade of the WOX family, and a previous study shows that WOX13 orthologs in the moss Physcomitrium patens (PpWOX13L) are involved in cellular reprogramming at wound sites. We found that the Arabidopsis wox13 mutant is totally defective in establishing organ reconnection upon grafting, suggesting that WOX13 is crucial for tissue repair in seed plants. WOX13 expression rapidly induced upon wounding, which was partly dependent on the activity of an AP2/ERF transcription factor, WOUND-INDUCED DEDIFFERENTIATION 1 (WIND1). WOX13 in turn directly upregulated WIND2 and WIND3 to further promote cellular reprogramming and organ regeneration. We also found that WOX13 orchestrates the transcriptional induction of cell wall-modifying enzyme genes, such as GLYCOSYL HYDROLASE 9Bs, PECTATE LYASE LIKEs and EXPANSINs. Furthermore, the chemical composition of cell wall monosaccharides was markedly different in the wox13 mutant. These data together suggest that WOX13 modifies cell wall properties, which may facilitate efficient callus formation and organ reconnection. Furthermore, we found that PpWOX13L complements the Arabidopsis wox13 mutant, suggesting that the molecular function of WOX13 is partly conserved between mosses and seed plants. This study provides key insights into the conservation and functional diversification of the WOX gene family during land plant evolution., (© The Author(s) 2021. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Stunted growth in saline conditions is a signature phenotype of the Arabidopsis SALT OVERLY SENSITIVE mutants (sos1-5) affected in pathways regulating the salt stress response. One of the mutants isolated, sos4, encodes a kinase that phosphorylates pyridoxal (PL), a B6 vitamer, forming the important coenzyme pyridoxal 5'-phosphate (PLP). Here, we show that sos4-1 and more recently isolated alleles are deficient in phosphorylated B6 vitamers including PLP. This deficit is concomitant with a lowered PL level. Ionomic profiling of plants under standard laboratory conditions (without salt stress) reveals that sos4 mutants are perturbed in mineral nutrient homeostasis, with a hyperaccumulation of transition metal micronutrients particularly in the root, accounting for stress sensitivity. This is coincident with the accumulation of reactive oxygen species, as well as enhanced lignification and suberization of the endodermis, although the Casparian strip is intact and functional. Further, micrografting shows that SOS4 activity in the shoot is necessary for proper root development. Growth under very low light alleviates the impairments, including salt sensitivity, suggesting that SOS4 is important for developmental processes under moderate light intensities. Our study provides a basis for the integration of SOS4 derived B6 vitamers into plant health and fitness., (© American Society of Plant Biologists 2021. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Somatic embryogenesis (SE) represents the most appropriate tool for next-generation breeding methods in woody plants such as grapevine (Vitis vinifera L.). However, in this species, the SE competence is strongly genotype-dependent and the molecular basis of this phenomenon is poorly understood. We explored the genetic and epigenetic basis of SE in grapevine by profiling the transcriptome, epigenome, and small RNAome of undifferentiated, embryogenic, and non-embryogenic callus tissues derived from two genotypes differing in competence for SE, Sangiovese and Cabernet Sauvignon. During the successful formation of embryonic callus, we observed the upregulation of epigenetic-related transcripts and short interfering RNAs in association with DNA hypermethylation at transposable elements in both varieties. Nevertheless, the switch to nonembryonic development matched the incomplete reinforcement of transposon silencing, and the evidence of such effect was more apparent in the recalcitrant Cabernet Sauvignon. Transcriptomic differences between the two genotypes were maximized already at early stage of culture where the recalcitrant variety expressed a broad panel of genes related to stress responses and secondary metabolism. Our data provide a different angle on the SE molecular dynamics that can be exploited to leverage SE as a biotechnological tool for fruit crop breeding., (© American Society of Plant Biologists 2021. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The programs associated with embryonic roots (ERs), primary roots (PRs), lateral roots (LRs), and adventitious roots (ARs) play crucial roles in the growth and development of roots in plants. The root functions are involved in diverse processes such as water and nutrient absorption and their utilization, the storage of photosynthetic products, and stress tolerance. Hormones and signaling pathways play regulatory roles during root development. Among these, auxin is the most important hormone regulating root development. The target of rapamycin (TOR) signaling pathway has also been shown to play a key role in root developmental programs. In this article, the milestones and influential progress of studying crosstalk between auxin and TOR during the development of ERs, PRs, LRs and ARs, as well as their functional implications in root morphogenesis, development, and architecture, are systematically summarized and discussed.

The development of above-ground lateral organs is initiated at the peripheral zone of the shoot apical meristem (SAM). The coordination of cell fate determination and the maintenance of stem cells are achieved through a complex regulatory network comprised of transcription factors. Two AP2/ERF transcription factor family genes, ESR1/DRN and ESR2/DRNL/SOB/BOL , regulate cotyledon and flower formation and de novo organogenesis in tissue culture. However, their roles in post-embryonic lateral organ development remain elusive. In this study, we analyzed the genetic interactions among SAM-related genes, WUS and STM , two ESR genes, and one of the HD-ZIP III members, REV , whose protein product interacts with ESR1 in planta. We found that esr1 mutations substantially enhanced the wus and stm phenotypes, which bear a striking resemblance to those of the wus rev and stm rev double mutants, respectively. Aberrant adaxial-abaxial polarity is observed in wus   esr1 at relatively low penetrance. On the contrary, the esr2 mutation partially suppressed stm phenotypes in the later vegetative phase. Such complex genetic interactions appear to be attributed to the distinct expression pattern of two ESR genes because the ESR1 promoter-driving ESR2 is capable of rescuing phenotypes caused by the esr1 mutation. Our results pose the unique genetic relevance of ESR1 and the SAM-related gene interactions in the development of rosette leaves.

Crown roots are essential for plants to obtain water and nutrients, perceive environmental changes, and synthesize plant hormones. In this study, we identified and characterized short crown root 8 ( scr8 ), which exhibited a defective phenotype of crown root and vegetative development. Temperature treatment showed that scr8 was sensitive to temperature and that the mutant phenotypes were rescued when grown under low temperature condition (20 °C). Histological and EdU staining analysis showed that the crown root formation was hampered and that the root meristem activity was decreased in scr8 . With map-based cloning strategy, the SCR8 gene was fine-mapped to an interval of 126.4 kb on chromosome 8. Sequencing analysis revealed that the sequence variations were only found in LOC_Os08g14850 , which encodes a CC-NBS-LRR protein. Expression and inoculation test analysis showed that the expression level of LOC_Os08g14850 was significantly decreased under low temperature (20 °C) and that the resistance to Xanthomonas oryzae pv. Oryzae ( Xoo ) was enhanced in scr8 . These results indicated that LOC_Os08g14850 may be the candidate of SCR8 and that its mutation activated the plant defense response, resulting in a crown root growth defect.

De novo shoot organogenesis is an important biotechnological tool for fundamental studies in plant. However, it is difficult in most bamboo species, and the genetic control of this highly dynamic and complicated regeneration process remains unclear. In this study, based on an in-depth analysis at the cellular level, the shoot organogenesis from calli of Ma bamboo (Dendrocalamus latiflorus Munro) was divided into five stages. Subsequently, single-molecule long-read isoform sequencing of tissue samples pooled from all five stages was performed to generate a full-length transcript landscape. A total of 83 971 transcripts, including 73 209 high-quality full-length transcripts, were captured, which served as an annotation reference for the subsequent RNA sequencing analysis. Time-course transcriptome analysis of samples at the abovementioned five stages was conducted to investigate the global gene expression atlas showing genome-wide expression of transcripts during the course of bamboo shoot organogenesis. K-means clustering analysis and stage-specific transcript identification revealed important dynamically expressed transcription regulators that function in bamboo shoot organogenesis. The majority of abiotic stress-responsive genes altered their expression levels during this process, and further experiments demonstrated that exogenous application of moderate but not severe abiotic stress increased the shoot regeneration efficiency. In summary, our study provides an overview of the genetic flow dynamics during bamboo shoot organogenesis. Full-length cDNA sequences generated in this study can serve as a valuable resource for fundamental and applied research in bamboo in the future., (© 2021 Society for Experimental Biology and John Wiley & Sons Ltd.)

Parasitic plants reduce crop yield worldwide. Dodder (Cuscuta campestris) is a stem parasite that attaches to its host, using haustoria to extract nutrients and water. We analyzed the transcriptome of six C. campestris tissues and identified a key gene, LATERAL ORGAN BOUNDARIES DOMAIN 25 (CcLBD25), as highly expressed in prehaustoria and haustoria. Gene coexpression networks from different tissue types and laser-capture microdissection RNA-sequencing data indicated that CcLBD25 could be essential for regulating cell wall loosening and organogenesis. We employed host-induced gene silencing by generating transgenic tomato (Solanum lycopersicum) hosts that express hairpin RNAs to target and down-regulate CcLBD25 in the parasite. Our results showed that C. campestris growing on CcLBD25 RNAi transgenic tomatoes transited to the flowering stage earlier and had reduced biomass compared with C. campestris growing on wild-type (WT) hosts, suggesting that parasites growing on transgenic plants were stressed due to insufficient nutrient acquisition. We developed an in vitro haustorium system to assay the number of prehaustoria produced on strands from C. campestris. Cuscuta campestris grown on CcLBD25 RNAi tomatoes produced fewer prehaustoria than those grown on WT tomatoes, indicating that down-regulating CcLBD25 may affect haustorium initiation. Cuscuta campestris haustoria growing on CcLBD25 RNAi tomatoes exhibited reduced pectin digestion and lacked searching hyphae, which interfered with haustorium penetration and formation of vascular connections. The results of this study elucidate the role of CcLBD25 in haustorium development and might contribute to developing parasite-resistant crops., (© The Author(s) 2021. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Postembryonic organogenesis is critical for plant development. Underground, lateral roots (LRs) form the bulk of mature root systems, yet the ontogeny of the LR primordium (LRP) is not clear. In this study, we performed the single-cell RNA sequencing through the first four stages of LR formation in Arabidopsis. Our analysis led to a model in which a single group of precursor cells, with a cell identity different from their pericycle origins, rapidly reprograms and splits into a mixed ground tissue/stem cell niche fate and a vascular precursor fate. The ground tissue and stem cell niche fates soon separate and a subset of more specialized vascular cells form sucrose transporting phloem cells that appear to connect to the primary root. We did not detect cells resembling epidermis or root cap, suggesting that outer tissues may form later, preceding LR emergence. At this stage, some remaining initial precursor cells form the primordium flanks, while the rest create a reservoir of pluripotent cells that are able to replace the LR if damaged. Laser ablation of the central and lateral LRP regions showed that remaining cells restart the sequence of tissue initiation to form a LR. Collectively, our study reveals an ontological hierarchy for LR formation with an early and sequential split of main root tissues and stem cells., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

The appearance of plant organs mediated the explosive radiation of land plants, which shaped the biosphere and allowed the establishment of terrestrial animal life. The evolution of organs and immobile gametes required the coordinated acquisition of novel gene functions, the co-option of existing genes and the development of novel regulatory programmes. However, no large-scale analyses of genomic and transcriptomic data have been performed for land plants. To remedy this, we generated gene expression atlases for various organs and gametes of ten plant species comprising bryophytes, vascular plants, gymnosperms and flowering plants. A comparative analysis of the atlases identified hundreds of organ- and gamete-specific orthogroups and revealed that most of the specific transcriptomes are significantly conserved. Interestingly, our results suggest that co-option of existing genes is the main mechanism for evolving new organs. In contrast to female gametes, male gametes showed a high number and conservation of specific genes, which indicates that male reproduction is highly specialized. The expression atlas capturing pollen development revealed numerous transcription factors and kinases essential for pollen biogenesis and function., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

Flowering plants display a vast diversity of flowering time and inflorescence architecture, which plays an important role in determining seed yield and fruit production. However, the molecular mechanism underlying the flowering control and compound inflorescence development, especially in legumes, remain to be elucidated. Here, we reported the identification of MtFDa, an essential regulator of flowering in the model legume Medicago truncatula. Mutation of MtFDa, led to the late flowering, abnormal secondary inflorescences as well as severe floral organ defects. Biochemical and molecular analyses revealed that MtFDa physically interacts with M. truncaula FLOWERING LOCUS T homolog, MtFTa1, a key regulator of Medicago flowering time, and this interaction facilitates MtFDa's function in activating the expression of MtSOC1a. Moreover, we demonstrated that MtFDa may affect secondary inflorescence development via regulating MtFULc expression in M. truncatula. Our findings help elucidate the mechanism of MtFDa-mediated regulation of flowering time and inflorescence development and provide insights into understanding the genetic regulatory network underlying complex productive development in legumes., (Copyright © 2021. Published by Elsevier GmbH.)

Many tuber and storage root crops owing to their high nutritional values offer high potential to overcome food security issues. The lack of information regarding molecular mechanisms that govern belowground storage organ development (except a tuber crop, potato) has limited the application of biotechnological strategies for improving storage crop yield. Phytohormones like gibberellin and cytokinin are known to play a crucial role in governing potato tuber development. Another phytohormone, auxin has been shown to induce tuber initiation and growth, and its crosstalk with gibberellin and strigolactone in a belowground modified stem (stolon) contributes to the overall potato tuber yield. In this review, we describe the crucial role of auxin biology in development of potato tubers. Considering the emerging reports from commercially important storage root crops (sweet potato, cassava, carrot, sugar beet and radish), we propose the function of auxin and related gene regulatory network in storage root development. The pattern of auxin content of stolon during various stages of potato tuber formation appears to be consistent with its level in various developmental stages of storage roots. We have also put-forward the potential of three-way interaction between auxin, strigolactone and mycorrhizal fungi in tuber and storage root development. Overall, we propose that auxin gene regulatory network and its crosstalk with other phytohormones in stolons/roots could govern belowground tuber and storage root development., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Lateral root (LR) formation is an example of a plant post-embryonic organogenesis event. LRs are issued from non-dividing cells entering consecutive steps of formative divisions, proliferation and elongation. The chromatin remodeling protein PICKLE (PKL) negatively regulates auxin-mediated LR formation through a mechanism that is not yet known. Here we show that PKL interacts with RETINOBLASTOMA-RELATED 1 (RBR1) to repress the LATERAL ORGAN BOUNDARIES-DOMAIN 16 ( LBD16) promoter activity. Since LBD16 function is required for the formative division of LR founder cells, repression mediated by the PKL-RBR1 complex negatively regulates formative division and LR formation. Inhibition of LR formation by PKL-RBR1 is counteracted by auxin, indicating that, in addition to auxin-mediated transcriptional responses, the fine-tuned process of LR formation is also controlled at the chromatin level in an auxin-signaling dependent manner.

A protocol for high-frequency direct organogenesis from root explants of Kachai lemon (Citrus jambhiri Lush.) was developed. Full-length roots (~3 cm) were isolated from the in vitro grown seedlings and cultured on Murashige and Skoog basal medium supplemented with Nitsch vitamin (MSN) with different concentrations of cytokinin [6-benzylaminopurine, (BAP)] and gibberellic acid (GA3). The frequency of multiple shoot proliferation was very high, with an average of 34.3 shoots per root explant when inoculated on the MSN medium supplemented with BAP (1.0 mg L-1) and GA3 (1.0 mg L-1). Optimal rooting was induced in the plantlets under half strength MSN medium supplemented with indole-3-acetic acid (IAA, 0.5-1.0 mg L-1). IAA induced better root structure than 1-naphthaleneacetic acid (NAA), which was evident from the scanning electron microscopy (SEM). The expressions of growth regulating factor genes (GRF1 and GRF5) and GA3 signaling genes (GA2OX1 and KO1) were elevated in the regenerants obtained from MSN+BAP (1.0 mg L-1)+GA3 (1.0 mg L-1). The expressions of auxin regulating genes were high in roots obtained in ½ MSN+IAA 1.0 mg L-1. Furthermore, indexing of the regenerants confirmed that there was no amplicons detected for Huanglongbing bacterium and Citrus tristeza virus. Random amplified polymorphic DNA (RAPD) and inter simple sequence repeat (ISSR) markers detected no polymorphic bands amongst the regenerated plants. This is the first report that describes direct organogenesis from the root explant of Citrus jambhiri Lush. The high-frequency direct regeneration protocol in the present study provides an enormous significance in Citrus organogenesis, its commercial cultivation and genetic conservation., Competing Interests: The authors have declared that no competing interests exist.

The ability to restore or replace injured tissues can be undoubtedly named among the most spectacular achievements of plant organisms. One of such regeneration pathways is organogenesis, the formation of individual organs from nonmeristematic tissue sections. The process can be triggered in vitro by incubation on medium supplemented with phytohormones. Cytokinins are a class of phytohormones demonstrating pleiotropic effects and a powerful network of molecular interactions. The present study reviews existing knowledge on the possible sequence of molecular and genetic events behind de novo shoot organogenesis initiated by cytokinins. Overall, the review aims to collect reactions encompassed by cytokinin primary responses, starting from phytohormone perception by the dedicated receptors, to transcriptional reprogramming of cell fate by the last module of multistep-phosphorelays. It also includes a brief reminder of other control mechanisms, such as epigenetic reprogramming.

Somatic polyploidy or endopolyploidy is common in the plant kingdom; it ensures growth and allows adaptation to the environment. It is present in the majority of plant groups, including mosses. Endopolyploidy had only been previously studied in about 65 moss species, which represents less than 1% of known mosses. We analyzed 11 selected moss species to determine the spatial and temporal distribution of endopolyploidy using flow cytometry to identify patterns in ploidy levels among gametophytes and sporophytes. All of the studied mosses possessed cells with various ploidy levels in gametophytes, and four of six species investigated in sporophytic stage had endopolyploid sporophytes. The proportion of endopolyploid cells varied among organs, parts of gametophytes and sporophytes, and ontogenetic stages. Higher ploidy levels were seen in basal parts of gametophytes and sporophytes than in apical parts. Slight changes in ploidy levels were observed during ontogenesis in cultivated mosses; the youngest (apical) parts of thalli tend to have lower levels of endopolyploidy. Differences between parts of cauloid and phylloids of Plagiomnium ellipticum and Polytrichum formosum were also documented; proximal parts had higher levels of endopolyploidy than distal parts. Endopolyploidy is spatially and temporally differentiated in the gametophytes of endopolyploid mosses and follows a pattern similar to that seen in angiosperms.

A key challenge in biology is to understand how the regional control of cell growth gives rise to final organ forms. Plant leaves must coordinate growth along both the proximodistal and mediolateral axes to produce their final shape. However, the cell-level mechanisms controlling this coordination remain largely unclear. Here, we show that, in A. thaliana, WOX5, one of the WUSCHEL-RELATED HOMEOBOX (WOX) family of homeobox genes, acts redundantly with WOX1 and WOX3 (PRESSED FLOWER [PRS]) to control leaf shape. Through genetics and hormone measurements, we find that these WOXs act in part through the regional control of YUCCA (YUC) auxin biosynthetic gene expression along the leaf margin. The requirement for WOX-mediated YUC expression in patterning of leaf shape cannot be bypassed by the epidermal expression of YUC, indicating that the precise domain of auxin biosynthesis is important for leaf form. Using time-lapse growth analysis, we demonstrate that WOX-mediated auxin biosynthesis organizes a proximodistal growth gradient that promotes lateral growth and consequently the characteristic ellipsoid A. thaliana leaf shape. We also provide evidence that WOX proteins shape the proximodistal gradient of differentiation by inhibiting differentiation proximally in the leaf blade and promoting it distally. This regulation allows sustained growth of the blade and enables a leaf to attain its final form. In conclusion, we show that the WOX/auxin regulatory module shapes leaf form by coordinating growth along the proximodistal and mediolateral leaf axes., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.)

Temperature is one of the most impactful environmental factors to which plants adjust their growth and development. Although the regulation of temperature signaling has been extensively investigated for the aerial part of plants, much less is known and understood about how roots sense and modulate their growth in response to fluctuating temperatures. Here, we found that shoot and root growth responses to high ambient temperature are coordinated during early seedling development in Arabidopsis A shoot signaling module that includes HY5, the phytochromes and the PIFs exerts a central function in coupling these growth responses and maintaining auxin levels in the root. In addition to the HY5/PIF-dependent shoot module, a regulatory axis composed of auxin biosynthesis and auxin perception factors controls root responses to high ambient temperature. Taken together, our findings show that shoot and root developmental responses to temperature are tightly coupled during thermomorphogenesis and suggest that roots integrate energy signals with local hormonal inputs., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2020. Published by The Company of Biologists Ltd.)

WUSCHEL-related homeobox4 (WOX4) plays important roles in vascular formation and adventitious root (AR) development. Here, we cloned the WOX4 from the AR of Larix kaempferi, whose cDNA is 1452 bp in length and encodes 483 amino acids. LkWOX4 is mainly expressed in the layer formation area of the stem at 10 days after cutting and its expression levels in the middles and ends of the ARs were higher than that in the AR tips. The fused protein LkWOX4-GFP localized in the nucleus. The heterologous overexpression of LkWOX4 in 84 K poplar significantly increased AR numbers and decreased AR lengths. In LkWOX4 plants, the endogenous jasmonic acid and abscisic acid contents significantly decreased in stems, while the auxin, jasmonic acid and abscisic acid contents significantly increased in ARs. RNA-Seq of those LkWOX4 overexpression poplar plants showed that the expression of plant hormone signaling genes (ARF2, ARF3, ARF7 and ARF18), rooting-related transcription factors (WOX5, LBD29 and SCR) and root development-related genes (CYCD3, GRF1 and TAA1) were affected. Moreover, we found that LkWOX4 interacts with LkPAT18, LkACBP6, and LkCIP7 using yeast two hybrid screening. Thus, we found LkWOX4 involves in the AR initiation and development, which might be regulated through the IAA, JA and ABA signaling pathways., 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 © 2020. Published by Elsevier B.V.)

SMALL AUXIN-UP RNA s ( SAUR s) comprise the largest family of early auxin response genes. Some SAURs have been reported to play important roles in plant growth and development, but their functional relationships with auxin signaling remain unestablished. Here, we report Arabidopsis ( Arabidopsis thaliana ) SAUR15 acts downstream of the auxin response factors ARF6,8 and ARF7,19 to regulate auxin signaling-mediated lateral root (LR) and adventitious root (AR) formation. The loss-of-function mutant saur15-1 exhibits fewer LRs and ARs. By contrast, plants overexpressing SAUR15 exhibit more LRs and ARs. We find that the SAUR15 promoter contains four tandem auxin-responsive elements, which are directly bound by ARF6 and ARF7 and are essential for SAUR15 expression. LR and AR impairment in arf6 and arf7 mutants is partially reduced by ectopic expression of SAUR15 Additionally, we demonstrate that the ARF6,7-upregulated SAUR15 promotes LR and AR development using two mechanisms. On the one hand, SAUR15 interacts with PP2C-D subfamily type 2C protein phosphatases to inhibit their activities, thereby stimulating plasma membrane H + -ATPases, which drives cell expansion and facilitates LR and AR formation. On the other hand, SAUR15 promotes auxin accumulation, potentially by inducing the expression of auxin biosynthesis genes. A resulting increase in free auxin concentration likely triggers LR and AR formation, forming a feedback loop. Our study provides insights and a better understanding of how SAURs function at the molecular level in regulating auxin-mediated LR and AR development., (© 2020 American Society of Plant Biologists. All Rights Reserved.)

Root development is important for normal plant growth and nutrient absorption. Studies have revealed the involvement of various factors in this complex process, improving our understanding of the relevant regulatory mechanisms. Here, we functionally characterize the role of Arabidopsis ( Arabidopsis thaliana ) phosphatidylinositol 4-kinase γ2 (PI4Kγ2) in root elongation regulation, which functions to modulate stability of the RING-type E3 ligase MYB30-INTERACTING E3 LIGASE1 (MIEL1) and auxin metabolism. Mutant plants deficient in PI4Kγ2 ( pi4kγ2 ) exhibited a shortened root length and elongation zone due to reduced auxin level. PI4Kγ2 was shown to interact with MIEL1, regulating its degradation and furthering the stability of transcription factor MYB30 (which suppresses auxin metabolism by directly binding to promoter regions of GH3 2 and GH3 6 ). Interestingly, pi4kγ2 plants presented altered hypersensitive response, indicating that PI4Kγ2 regulates synergetic growth and defense of plants through modulating auxin metabolism. These results reveal the importance of protein interaction in regulating ubiquitin-mediated protein degradation in eukaryotic cells, and illustrate a mechanism coordinating plant growth and biotic stress response., (© 2020 American Society of Plant Biologists. All Rights Reserved.)

An evolutionarily ancient plant hormone receptor complex comprising the α/β-fold hydrolase receptor KARRIKIN INSENSITIVE 2 (KAI2) and the F-box protein MORE AXILLARY GROWTH 2 (MAX2) mediates a range of developmental responses to smoke-derived butenolides called karrikins (KARs) and to yet elusive endogenous KAI2 ligands (KLs). Degradation of SUPPRESSOR OF MAX2 1 (SMAX1) after ligand perception is considered to be a key step in KAR/KL signaling. However, molecular events which regulate plant development downstream of SMAX1 removal have not been identified. Here we show that Lotus japonicus SMAX1 is specifically degraded in the presence of KAI2 and MAX2 and plays an important role in regulating root and root hair development. smax1 mutants display very short primary roots and elongated root hairs. Their root transcriptome reveals elevated ethylene responses and expression of ACC Synthase 7 ( ACS7 ), which encodes a rate-limiting enzyme in ethylene biosynthesis. smax1 mutants release increased amounts of ethylene and their root phenotype is rescued by treatment with ethylene biosynthesis and signaling inhibitors. KAR treatment induces ACS7 expression in a KAI2-dependent manner and root developmental responses to KAR treatment depend on ethylene signaling. Furthermore, in Arabidopsis , KAR-induced root hair elongation depends on ACS7 Thus, we reveal a connection between KAR/KL and ethylene signaling in which the KAR/KL signaling module (KAI2-MAX2-SMAX1) regulates the biosynthesis of ethylene to fine-tune root and root hair development, which are important for seedling establishment at the beginning of the plant life cycle., Competing Interests: The authors declare no competing interest.

Arabidopsis AINTEGUMENTA (ANT), an AP2 transcription factor, is known to control plant growth and floral organogenesis. In this study, our transcriptome analysis and in situ hybridization assays of maize embryonic leaves suggested that maize ANT1 (ZmANT1) regulates vascular development. To better understand ANT1 functions, we determined the binding motif of ZmANT1 and then showed that ZmANT1 binds the promoters of millet SCR1 , GNC , and AN3 , which are key regulators of Kranz anatomy, chloroplast development, and plant growth, respectively. We generated a mutant with a single-codon deletion and two frameshift mutants of the ANT1 ortholog in the C4 millet Setaria viridis by the CRISPR/Cas9 technique. The two frameshift mutants displayed reduced photosynthesis efficiency and growth rate, smaller leaves, and lower grain yields than wild-type (WT) plants. Moreover, their leaves sporadically exhibited distorted Kranz anatomy and vein spacing. Conducting transcriptomic analysis of developing leaves in the WT and the three mutants we identified differentially expressed genes (DEGs) in the two frameshift mutant lines and found many down-regulated DEGs enriched in photosynthesis, heme, tetrapyrrole binding, and antioxidant activity. In addition, we predicted many target genes of ZmANT1 and chose 13 of them to confirm binding of ZmANT1 to their promoters. Based on the above observations, we proposed a model for ANT1 regulation of cell proliferation and leaf growth, vascular and vein development, chloroplast development, and photosynthesis through its target genes. Our study revealed biological roles of ANT1 in several developmental processes beyond its known roles in plant growth and floral organogenesis., Competing Interests: The authors declare no competing interest.

mRNA methylation at the N6- position of adenosine (m 6 A) enables multiple layers of post-transcriptional gene control, often via RNA-binding proteins that use a YT521-B homology (YTH) domain for specific m 6 A recognition. In Arabidopsis , normal leaf morphogenesis and rate of leaf formation require m 6 A and the YTH-domain proteins ECT2, ECT3 and ECT4. In this study, we show that ect2/ect3 and ect2/ect3/ect4 mutants also exhibit slow root and stem growth, slow flower formation, defective directionality of root growth, and aberrant flower and fruit morphology. In all cases, the m 6 A-binding site of ECT proteins is required for in vivo function. We also demonstrate that both m 6 A methyltransferase mutants and ect2/ect3/ect4 exhibit aberrant floral phyllotaxis. Consistent with the delayed organogenesis phenotypes, we observe particularly high expression of ECT2 , ECT3 and ECT4 in rapidly dividing cells of organ primordia. Accordingly, ect2/ect3/ect4 mutants exhibit decreased rates of cell division in leaf and vascular primordia. Thus, the m 6 A-ECT2/ECT3/ECT4 axis is employed as a recurrent module to stimulate plant organogenesis, at least in part by enabling rapid cellular proliferation., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2020. Published by The Company of Biologists Ltd.)

Reproduction-specific small RNAs are vital regulators of germline development in animals and plants. MicroRNA2118 (miR2118) is conserved in plants and induces the production of phased small interfering RNAs (phasiRNAs). To reveal the biological functions of miR2118, we describe here rice mutants with large deletions of the miR2118 cluster. Our results demonstrate that the loss of miR2118 causes severe male and female sterility in rice, associated with marked morphological and developmental abnormalities in somatic anther wall cells. Small RNA profiling reveals that miR2118-dependent 21-nucleotide (nt) phasiRNAs in the anther wall are U-rich, distinct from the phasiRNAs in germ cells. Furthermore, the miR2118-dependent biogenesis of 21-nt phasiRNAs may involve the Argonaute proteins OsAGO1b/OsAGO1d, which are abundant in anther wall cell layers. Our study highlights the site-specific differences of phasiRNAs between somatic anther wall and germ cells, and demonstrates the significance of miR2118/U-phasiRNA functions in anther wall development and rice reproduction.

Root system architecture (RSA) is required for the acquisition of water and mineral nutrients from the soil. One of the essential nutrients, nitrate (NO 3 - ), is sensed and transported by nitrate transporters NRT1.1 and NRT2.1 in the plants. Nitrate transporter 1.1 ( NRT1.1 ) is a dual-affinity nitrate transporter phosphorylated at the T101 residue by calcineurin B-like interacting protein kinase (CIPKs); it also regulates the expression of other key nitrate assimilatory genes. The differential phosphorylation (phosphorylation and dephosphorylation) strategies and underlying Ca 2+ signaling mechanism of NRT1.1 stimulate lateral root growth by activating the auxin transport activity and Ca 2+ -ANR1 signaling at the plasma membrane and the endosomes, respectively. NO 3 - additionally functions as a signal molecule that forms a signaling system, which consists of a vast array of transcription factors that control root system architecture that either stimulate or inhibit lateral and primary root development in response to localized and high nitrate (NO 3 - ), respectively. This review elucidates the so-far identified nitrate transporters, nitrate sensing, signal transduction, and the key roles of nitrate transporters and its downstream transcriptional regulatory network in the primary and lateral root development in Arabidopsis thaliana under stress conditions.

Organ size and shape are precisely regulated to ensure proper function. The four sepals in each Arabidopsis thaliana flower must maintain the same size throughout their growth to continuously enclose and protect the developing bud. Here we show that DEVELOPMENT RELATED MYB-LIKE 1 (DRMY1) is required for both timing of organ initiation and proper growth, leading to robust sepal size in Arabidopsis. Within each drmy1 flower, the initiation of some sepals is variably delayed. Late-initiating sepals in drmy1 mutants remain smaller throughout development, resulting in variability in sepal size. DRMY1 focuses the spatiotemporal signalling patterns of the plant hormones auxin and cytokinin, which jointly control the timing of sepal initiation. Our findings demonstrate that timing of organ initiation, together with growth and maturation, contribute to robust organ size.

Positional information is essential for coordinating the development of multicellular organisms. In plants, positional information provided by the hormone auxin regulates rhythmic organ production at the shoot apex, but the spatio-temporal dynamics of auxin gradients is unknown. We used quantitative imaging to demonstrate that auxin carries high-definition graded information not only in space but also in time. We show that, during organogenesis, temporal patterns of auxin arise from rhythmic centrifugal waves of high auxin travelling through the tissue faster than growth. We further demonstrate that temporal integration of auxin concentration is required to trigger the auxin-dependent transcription associated with organogenesis. This provides a mechanism to temporally differentiate sites of organ initiation and exemplifies how spatio-temporal positional information can be used to create rhythmicity., Competing Interests: CG, GC, JL, GB, RM, RA, VB, SM, CW, YJ, JL, CG, TV No competing interests declared, (© 2020, Galvan-Ampudia et al.)

Expansins are structural proteins prevalent in cell walls, participate in cell growth and stress responses by interacting with internal and external signals perceived by the genetic networks of plants. Herein, we investigated the Brassica rapa expansin-like B1 (BrEXLB1) interaction with phytohormones (IAA, ABA, Ethephon, CK, GA3, SA, and JA), genes ( Bra001852, Bra001958 , and Bra003006 ), biotic (Turnip mosaic Virus (TuMV), Pectobacterium carotovorum, clubroot disease), and abiotic stress (salt, oxidative, osmotic, and drought) conditions by either cDNA microarray or qRT-PCR assays. In addition, we also unraveled the potential role of BrEXLB1 in root growth, drought stress response, and seed germination in transgenic Arabidopsis and B. rapa lines. The qRT-PCR results displayed that BrEXLB1 expression was differentially influenced by hormones, and biotic and abiotic stress conditions; upregulated by IAA, ABA, SA, ethylene, drought, salt, osmotic, and oxidative conditions; and downregulated by clubroot disease, P. carotovorum, and TuMV infections. Among the tissues, prominent expression was observed in roots indicating the possible role in root growth. The root phenotyping followed by confocal imaging of root tips in Arabidopsis lines showed that BrEXLB1 overexpression increases the size of the root elongation zone and induce primary root growth. Conversely, it reduced the seed germination rate. Further analyses with transgenic B. rapa lines overexpressing BrEXLB1 sense (OX) and antisense transcripts (OX-AS) confirmed that BrEXLB1 overexpression is positively associated with drought tolerance and photosynthesis during vegetative growth phases of B. rapa plants. Moreover, the altered expression of BrEXLB1 in transgenic lines differentially influenced the expression of predicted BrEXLB1 interacting genes like Bra001852 and Bra003006. Collectively, this study revealed that BrEXLB1 is associated with root development, drought tolerance, photosynthesis, and seed germination.

In plants, the organ size is one of the most important features and regulated by an elaborate developmental program involving both internal and external signals. The steroidal hormone brassinosteroid (BR) plays an important role in regulating the organ size. BRASSINAZOLE RESISTANT 1 (BZR1) is one of important transcription factors that regulate organ size in BR signal pathway in Arabidopsis. The function of BZR1 on organ size is well characterized in Arabidopsis, but poorly understood in maize (Zea mays). To understand the mechanism of intrinsic organ size regulated by BZR1 during organogenesis, we identified the maize BZR1 and examined its function in Arabidopsis. Overexpression of ZmBZR1 displayed phenotypes of enlarged cotyledons, rosette leaves, floral organ and seed size in Arabidopsis. The cells in rosette leaves as well as other organs in transgenic ZmBZR1 lines were dramatically larger and longer than those in Col-0. ChIP and RNA-seq analysis showed ZmBZR1 can directly bind to the promoter region of organ size related genes, Germination Repression and Cell Expansion receptor-like kinase (GRACE) and KIP-RELATED PROTEIN6 (KRP6) to regulate their expression, suggesting ZmBZR1 is required for the progressive increase in cells during Arabidopsis development. Collectively, our findings provide significant insights into the mechanisms underlying regulation of organ size mediated by maize BZR1., Competing Interests: Declaration of Competing Interest The authors declare no conflicts of interest., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: Legumes can utilize atmospheric nitrogen by hosting nitrogen-fixing bacteria in special lateral root organs, called nodules. Legume nodules have a unique ontology, despite similarities in the gene networks controlling nodule and lateral root development. It has been shown that Medicago truncatula NODULE ROOT1 (MtNOOT1) is required for the maintenance of nodule identity, preventing the conversion to lateral root development. MtNOOT1 and its orthologs in other plant species -collectively called the NOOT-BOP-COCH-LIKE (NBCL) family- specify boundary formation in various aerial organs. However, MtNOOT1 is not only expressed in nodules and aerial organs, but also in developing roots, where its function remains elusive., Results: We show that Mtnoot1 mutant seedlings display accelerated root elongation due to an enlarged root apical meristem. Also, Mtnoot1 mutant roots are thinner than wild-type and are delayed in xylem cell differentiation. We provide molecular evidence that the affected spatial development of Mtnoot1 mutant roots correlates with delayed induction of genes involved in xylem cell differentiation. This coincides with a basipetal shift of the root zone that is susceptible to rhizobium-secreted symbiotic signal molecules., Conclusions: Our data show that MtNOOT1 regulates the size of the root apical meristem and vascular differentiation. Our data demonstrate that MtNOOT1 not only functions as a homeotic gene in nodule development but also coordinates the spatial development of the root.

De novo shoot regeneration is one of the important manifestations of cell totipotency in organogenesis, which reflects a survival strategy organism evolved when facing natural selection. Compared with tissue regeneration, and somatic embryogenesis, de novo shoot regeneration denotes a shoot regeneration process directly from detatched or injured tissues of plant. Studies on plant shoot regeneration had identified key genes mediating shoot regeneration. However, knowledge was derived from Arabidopsis ; the regeneration capacity is hugely distinct among species. To achieve a comprehensive understanding of the shoot regeneration mechanism from tree species, we select four genetic lines of Populus euphratica from a natural population to be sequenced at transcriptome level. On the basis of the large difference of differentiation capacity, between the highly differentiated (HD) and low differentiated (LD) groups, the analysis of differential expression identified 4920 differentially expressed genes (DEGs), which were revealed in five groups of expression patterns by clustering analysis. Enrichment showed crucial pathways involved in regulation of regeneration difference, including "plant hormone signal transduction", "cell differentiation", "cellular response to auxin stimulus", and "auxin-activated signaling pathway". The expression of nine genes reported to be associated with shoot regeneration was validated using quantitative real-time PCR (qRT-PCR). For the specificity of regeneration mechanism with P. euphratica , large amount of DEGs involved in "plant-pathogen interaction", ubiquitin-26S proteosome mediated proteolysis pathway, stress-responsive DEGs, and senescence-associated DEGs were summarized to possibly account for the differentiation difference with distinct genotypes of P. euphratica . The result in this study helps screening of key regulators in mediating the shoot differentiation. The transcriptomic characteristic in P. euphratica further enhances our understanding of key processes affecting the regeneration capacity of de novo shoots among distinct species., Competing Interests: The authors declare no conflict of interest.

To overcome nitrogen deficiencies in the soil, legumes enter symbioses with rhizobial bacteria that convert atmospheric nitrogen into ammonium. Rhizobia are accommodated as endosymbionts within lateral root organs called nodules that initiate from the inner layers of Medicago truncatula roots in response to rhizobial perception. In contrast, lateral roots emerge from predefined founder cells as an adaptive response to environmental stimuli, including water and nutrient availability. CYTOKININ RESPONSE 1 (CRE1)-mediated signaling in the pericycle and in the cortex is necessary and sufficient for nodulation, whereas cytokinin is antagonistic to lateral root development, with cre1 showing increased lateral root emergence and decreased nodulation. To better understand the relatedness between nodule and lateral root development, we undertook a comparative analysis of these two root developmental programs. Here, we demonstrate that despite differential induction, lateral roots and nodules share overlapping developmental programs, with mutants in LOB-DOMAIN PROTEIN 16 (LBD16) showing equivalent defects in nodule and lateral root initiation. The cytokinin-inducible transcription factor NODULE INCEPTION (NIN) allows induction of this program during nodulation through activation of LBD16 that promotes auxin biosynthesis via transcriptional induction of STYLISH (STY) and YUCCAs (YUC). We conclude that cytokinin facilitates local auxin accumulation through NIN promotion of LBD16, which activates a nodule developmental program overlapping with that induced during lateral root initiation., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Studies on the model plant Arabidopsis have led to the common view that lateral roots are exclusively formed from pericycle cells and that the latter are unique in their ability to be reprogrammed into stem cells. By analysing lateral root formation in an evolutionary context, we show that lateral root primordium formation in which cortex, endodermis and pericycle are mitotically activated, is a common and ancestral trait in seed plants, whereas the exclusive involvement of pericycle evolved in the Brassicaceae. Furthermore, the endodermis can also be reprogrammed into stem cells in some species., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2019. Published by The Company of Biologists Ltd.)

Several Bradyrhizobium species nodulate the leguminous plant Aeschynomene indica in a type III secretion system-dependent manner, independently of Nod factors. To date, the underlying molecular determinants involved in this symbiotic process remain unknown. To identify the rhizobial effectors involved in nodulation, we mutated 23 out of the 27 effector genes predicted in Bradyrhizobium strain ORS3257. The mutation of nopAO increased nodulation and nitrogenase activity, whereas mutation of 5 other effector genes led to various symbiotic defects. The nopM1 and nopP1 mutants induced a reduced number of nodules, some of which displayed large necrotic zones. The nopT and nopAB mutants induced uninfected nodules, and a mutant in a yet-undescribed effector gene lost the capacity for nodule formation. This effector gene, widely conserved among bradyrhizobia, was named ernA for "effector required for nodulation-A." Remarkably, expressing ernA in a strain unable to nodulate A. indica conferred nodulation ability. Upon its delivery by Pseudomonas fluorescens into plant cells, ErnA was specifically targeted to the nucleus, and a fluorescence resonance energy transfer-fluorescence lifetime imaging microscopy approach supports the possibility that ErnA binds nucleic acids in the plant nuclei. Ectopic expression of ernA in A. indica roots activated organogenesis of root- and nodule-like structures. Collectively, this study unravels the symbiotic functions of rhizobial type III effectors playing distinct and complementary roles in suppression of host immune functions, infection, and nodule organogenesis, and suggests that ErnA triggers organ development in plants by a mechanism that remains to be elucidated., Competing Interests: The authors declare no conflict of interest., (Copyright © 2019 the Author(s). Published by PNAS.)

In both plants and animals, multiple cellular processes must be orchestrated to ensure proper organogenesis. The cell division patterns control the shape of growing organs, yet how they are precisely determined and coordinated is poorly understood. In plants, the distribution of the phytohormone auxin is tightly linked to organogenesis, including lateral root (LR) development. Nevertheless, how auxin regulates cell division pattern during lateral root development remains elusive. Here, we report that auxin activates Mitogen-Activated Protein Kinase (MAPK) signaling via transmembrane kinases (TMKs) to control cell division pattern during lateral root development. Both TMK1/4 and MKK4/5-MPK3/6 pathways are required to properly orient cell divisions, which ultimately determine lateral root development in response to auxin. We show that TMKs directly and specifically interact with and phosphorylate MKK4/5, which is required for auxin to activate MKK4/5-MPK3/6 signaling. Our data suggest that TMK-mediated noncanonical auxin signaling is required to regulate cell division pattern and connect auxin signaling to MAPK signaling, which are both essential for plant development., Competing Interests: The authors declare no competing interest.

Unlike dicots, the robust root system in grass species largely originates from stem base during postembryonic development. The mechanisms by which plant hormone signaling pathways control the architecture of adventitious root remain largely unknown. Here, we studied the modulations in global genes activity in developing rice adventitious root by genome-wide RNA sequencing in response to external auxin and cytokinin signaling cues. We further analyzed spatiotemporal regulations of key developmental regulators emerged from our global transcriptome analysis. Interestingly, some of the key cell fate determinants such as homeodomain transcription factor (TF), OsHOX12, no apical meristem protein, OsNAC39, APETALA2/ethylene response factor, OsAP2/ERF-40 and WUSCHEL-related homeobox, OsWOX6.1 and OsWOX6.2, specifically expressed in adventitious root primordia. Functional analysis of one of these regulators, an auxin-induced TF containing AP2/ERF domain, OsAP2/ERF-40, demonstrates its sufficiency to confer the adventitious root fate. The ability to trigger the root developmental program is largely attributed to OsAP2/ERF-40-mediated dose-dependent transcriptional activation of genes that can facilitate generating effective auxin response, and OsERF3-OsWOX11-OsRR2 pathway. Our studies reveal gene regulatory network operating in response to hormone signaling pathways and identify a novel TF regulating adventitious root developmental program, a key agronomically important quantitative trait, upstream of OsERF3-OsWOX11-OsRR2 pathway., (� The Author(s) 2019. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.)