Search

The article explores the ancient role of flavonoids in land plants' adaptability to environmental stresses, highlighting their antioxidant properties and multifunctionality. Flavonoids have evolved to serve as defense mechanisms against stressors, modulate plant growth and development, and potentially emerged in response to biotic pressures and UV protection. They also act as signaling molecules, influencing auxin movement and belowground organ growth in angiosperms, while regulating human cell growth and metabolism through protein activities. The document further discusses flavonoids' interactions with hormone signaling pathways, stress responses, and their contribution to plant adaptation in changing environments, shedding light on their diverse roles in plant biology and specialized metabolism. [Extracted from the article]

Summary The nonphototrophic hypocotyl 3 (NPH3) domain is plant specific and of unknown function. It is nearly always attached to an N‐terminal BTB domain and a largely unstructured C‐terminal region. Recent reports revealed NPH3‐domain GTPase activity and connection to intracellular trafficking, condensate formation, membrane attachment of the C‐terminal region for some NPH3‐domain proteins and, at the physiological level, drought‐related function for at least one NPH3‐domain protein. We integrate these new ideas of NPH3‐domain protein function into two, nonexclusive, working models: the ‘traffic director’ model, whereby NPH3‐domain proteins regulate intracellular trafficking and, the ‘hitchhiker’ model whereby NPH3‐domain proteins ride the trafficking system to find ubiquitination targets. Determining which model best applies to uncharacterized NPH3‐domain proteins will contribute to understanding intracellular trafficking and environmental responses. [ABSTRACT FROM AUTHOR]

Summary: Plants delicately regulate endogenous auxin levels through the coordination of transport, biosynthesis, and inactivation, which is crucial for growth and development. While it is well‐established that the actin cytoskeleton can regulate auxin levels by affecting polar transport, its potential role in auxin biosynthesis has remained largely unexplored.Using LC–MS/MS‐based methods combined with fluorescent auxin marker detection, we observed a significant increase in root auxin levels upon deletion of the actin bundling proteins AtFIM4 and AtFIM5. Fluorescent observation, immunoblotting analysis, and biochemical approaches revealed that AtFIM4 and AtFIM5 affect the protein abundance of the key auxin synthesis enzyme YUC8 in roots.AtFIM4 and AtFIM5 regulate the auxin synthesis enzyme YUC8 at the protein level, with its degradation mediated by the 26S proteasome. This regulation modulates auxin synthesis and endogenous auxin levels in roots, consequently impacting root development. Based on these findings, we propose a molecular pathway centered on the 'actin cytoskeleton‐26S proteasome‐YUC8‐auxin' axis that controls auxin levels.Our findings shed light on a new pathway through which plants regulate auxin synthesis. Moreover, this study illuminates a newfound role of the actin cytoskeleton in regulating plant growth and development, particularly through its involvement in maintaining protein homeostasis via the 26S proteasome. [ABSTRACT FROM AUTHOR]

Summary Plant root system is significantly influenced by high soil levels of ammonium nitrogen, leading to reduced root elongation and enhanced lateral root branching. In Arabidopsis, these processes have been reported to be mediated by phytohormones and their downstream signaling pathways, while the controlling mechanisms remain elusive in crops. Through a transcriptome analysis of roots subjected to high/low ammonium treatments, we identified a cytokinin oxidase/dehydrogenase encoding gene, CKX3, whose expression is induced by high ammonium. Knocking out CKX3 and its homologue CKX8 results in shorter seminal roots, fewer lateral roots, and reduced sensitivity to high ammonium. Endogenous cytokinin levels are elevated by high ammonium or in ckx3 mutants. Cytokinin application results in shorter seminal roots and fewer lateral roots in wild‐type, mimicking the root responses of ckx3 mutants to high ammonium. Furthermore, CKX3 is transcriptionally activated by type‐B RR25 and RR26, and ckx3 mutants have reduced auxin content and signaling in roots under low ammonium. This study identified RR25/26‐CKX3‐cytokinin as a signal module that mediates root responses to external ammonium by modulating of auxin signaling in the root meristem and lateral root primordium. This highlights the critical role of cytokinin metabolism in regulating rice root development in response to ammonium. [ABSTRACT FROM AUTHOR]

Summary Extracellular auxin maxima and minima are important to control plant developmental programs. Auxin gradients are provided by the concerted action of proteins from the three major plasma membrane (PM) auxin transporter classes AUX1/LAX, PIN and ATP‐BINDING CASSETTE subfamily B (ABCB) transporters. But neither genetic nor biochemical nor modeling approaches have been able to reliably assign the individual roles and interplay of these transporter types. Based on the thermodynamic properties of the transporters, we show here by mathematical modeling and computational simulations that the concerted action of different auxin transporter types allows the adjustment of specific transmembrane auxin gradients. The dynamic flexibility of the ‘auxin homeostat’ comes at the cost of an energy‐consuming ‘auxin cycling’ across the membrane. An unexpected finding was that potential functional ABCB‐PIN synchronization appears to allow an optimization of the trade‐off between the speed of PM auxin gradient adjustment on the one hand and ATP consumption and disturbance of general anion homeostasis on the other. In conclusion, our analyses provide fundamental insights into the thermodynamic constraints and flexibility of transmembrane auxin transport in plants. [ABSTRACT FROM AUTHOR]

Summary: Maize silk is a specialized type of stigma, covered with numerous papillae for pollen grain capture. However, the developmental process of stigmatic papillae and the underlying regulatory mechanisms have remained largely unknown.Here, we combined the cytological, genetic and molecular studies to demonstrate that three homologous genes ZmSPL10, ZmSPL14 and ZmSPL26 play a central role in promoting stigmatic papilla formation in maize.We show that their triple knockout mutants are nearly complete lack of stigmatic papilla, resulting in a severe reduction in kernel setting. Cellular examination reveals that stigmatic papilla is developed from a precursor cell, which is the smaller daughter cell resulting from asymmetric cell division of a silk epidermal cell. In situ hybridization shows that ZmSPL10, ZmSPL14 and their target genes SPI1, ZmPIN1b, ZmARF28 and ZmWOX3A are preferentially expressed in the precursor cells of stigmatic papillae. Moreover, ZmSPL10, ZmSPL14 and ZmSPL26 directly bind to the promoters of SPI1, ZmPIN1b, ZmARF28 and ZmWOX3A and promote their expression. Further, Zmwox3a knockout mutants display severe defects in stigmatic papilla formation and reduced seed setting.Collectively, our results demonstrate that ZmSPL10, ZmSPL14 and ZmSPL26 act together to promote stigmatic papilla development through regulating auxin signaling and ZmWOX3A expression. [ABSTRACT FROM AUTHOR]

Summary Strengthening future food security through the application of unsustainable levels of inorganic nitrogen (N) fertilizers to crop fields may exacerbate environmental damage. Coordination of N‐use efficiency (NUE) and plant growth is, therefore, crucial for sustainable agriculture. Auxin plays pivotal roles in developmental and signaling responses that affect NUE. Hence, a better understanding of these processes provides great potential to improve crop NUE. This review summarizes the effects of auxin on N‐related and root developmental processes that either directly or indirectly affect NUE in the model plant Arabidopsis and major crop species to highlight the potential of fostering sustainable agricultural development in the future through modulating auxin‐related processes. [ABSTRACT FROM AUTHOR]

The vascular cambium is the main secondary meristem in plants that produces secondary phloem (outside) and xylem (inside) on opposing sides of the cambium. The phytohormone ethylene has been implicated in vascular cambium activity, but the regulatory network underlying ethylene-mediated cambial activity remains to be elucidated. Here, we found that PETAL MOVEMENT-RELATED PROTEIN1 (RhPMP1), an ethylene-inducible HOMEODOMAIN-LEUCINE ZIPPER I transcription factor in woody plant rose (Rosa hybrida), regulates local auxin biosynthesis and auxin transport to maintain cambial activity. Knockdown of RhPMP1 resulted in smaller midveins and reduced auxin content, while RhPMP1 overexpression resulted in larger midveins and increased auxin levels compared with the wild-type plants. Furthermore, we revealed that Indole-3-pyruvate monooxygenase YUCCA 10 (RhYUC10) and Auxin transporter-like protein 2 (RhAUX2), encoding an auxin biosynthetic enzyme and an auxin influx carrier, respectively, are direct downstream targets of RhPMP1. In summary, our results suggest that ethylene promotes an auxin maximum in the cambium adjacent to the xylem to maintain cambial activity.

Summary: Legume plants develop two types of root postembryonic organs, lateral roots and symbiotic nodules, using shared regulatory components. The module composed by the microRNA390, the Trans‐Acting SIRNA3 (TAS3) RNA and the Auxin Response Factors (ARF)2, ARF3, and ARF4 (miR390/TAS3/ARFs) mediates the control of both lateral roots and symbiotic nodules in legumes.Here, a transcriptomic approach identified a member of the Lateral Organ Boundaries Domain (LBD) family of transcription factors in Medicago truncatula, designated MtLBD17/29a, which is regulated by the miR390/TAS3/ARFs module. ChIP‐PCR experiments evidenced that MtARF2 binds to an Auxin Response Element present in the MtLBD17/29a promoter. MtLBD17/29a is expressed in root meristems, lateral root primordia, and noninfected cells of symbiotic nodules.Knockdown of MtLBD17/29a reduced the length of primary and lateral roots and enhanced lateral root formation, whereas overexpression of MtLBD17/29a produced the opposite phenotype. Interestingly, both knockdown and overexpression of MtLBD17/29a reduced nodule number and infection events and impaired the induction of the symbiotic genes Nodulation Signaling Pathway (NSP) 1 and 2.Our results demonstrate that MtLBD17/29a is regulated by the miR390/TAS3/ARFs module and a direct target of MtARF2, revealing a new lateral root regulatory hub recruited by legumes to act in the root nodule symbiotic program. [ABSTRACT FROM AUTHOR]

Summary: The conquest of land by plants was concomitant with, and possibly enabled by, the evolution of three‐dimensional (3D) growth. The moss Physcomitrium patens provides a model system for elucidating molecular mechanisms in the initiation of 3D growth. Here, we investigate whether the phytohormone ethylene, which is believed to have been a signal before land plant emergence, plays a role in 3D growth regulation in P. patens.We report ethylene controls 3D gametophore formation, based on results from exogenously applied ethylene and genetic manipulation of PpEIN2, which is a central component in the ethylene signaling pathway.Overexpression (OE) of PpEIN2 activates ethylene responses and leads to earlier formation of gametophores with fewer gametophores produced thereafter, phenocopying ethylene‐treated wild‐type. Conversely, Ppein2 knockout mutants, which are ethylene insensitive, show initially delayed gametophore formation with more gametophores produced later. Furthermore, pharmacological and biochemical analyses reveal auxin levels are decreased in the OE lines but increased in the knockout mutants.Our results suggest that evolutionarily, ethylene and auxin molecular networks were recruited to build the plant body plan in ancestral land plants. This might have played a role in enabling ancient plants to acclimate to the continental surfaces of the planet. [ABSTRACT FROM AUTHOR]

Summary: The potential for totipotency exists in all plant cells; however, the underlying mechanisms remain largely unknown. Earlier findings have revealed that the overexpression of LEAFY COTYLEDON 2 (LEC2) can directly trigger the formation of somatic embryos on the cotyledons of Arabidopsis. Furthermore, cotyledon cells that overexpress LEC2 accumulate significant lipid reserves typically found in seeds. The precise mechanisms and functions governing lipid accumulation in this process remain unexplored.In this study, we demonstrate that WRINKLED1 (WRI1), the key regulator of lipid biosynthesis, is essential for somatic embryo formation, suggesting that WRI1‐mediated lipid biosynthesis plays a crucial role in the transition from vegetative to embryonic development.Our findings indicate a direct interaction between WRI1 and LEC2, which enhances the enrichment of LEC2 at downstream target genes and stimulates their induction. Besides, our data suggest that WRI1 forms a complex with LEC1, LEC2, and FUSCA3 (FUS3) to facilitate the accumulation of auxin and lipid for the somatic embryo induction, through strengthening the activation of YUCCA4 (YUC4) and OLEOSIN3 (OLE3) genes.Our results uncover a regulatory module controlled by WRI1, crucial for somatic embryogenesis. These findings provide valuable insights into our understanding of plant cell totipotency. [ABSTRACT FROM AUTHOR]

Summary: Arabidopsis thaliana (Arabidopsis) shoot architecture is largely determined by the pattern of axillary buds that grow into lateral branches, the regulation of which requires integrating both local and systemic signals.Nodal explants – stem explants each bearing one leaf and its associated axillary bud – are a simplified system to understand the regulation of bud activation. To explore signal integration in bud activation, we characterised the growth dynamics of buds in nodal explants in key mutants and under different treatments.We observed that isolated axillary buds activate in two genetically and physiologically separable phases: a slow‐growing lag phase, followed by a switch to rapid outgrowth. Modifying BRANCHED1 expression or the properties of the auxin transport network, including via strigolactone application, changed the length of the lag phase. While most interventions affected only the length of the lag phase, strigolactone treatment and a second bud also affected the rapid growth phase.Our results are consistent with the hypothesis that the slow‐growing lag phase corresponds to the time during which buds establish canalised auxin transport out of the bud, after which they enter a rapid growth phase. Our work also hints at a role for auxin transport in influencing the maximum growth rate of branches. [ABSTRACT FROM AUTHOR]

Summary: Seasonal dynamics of root growth play an important role in large‐scale ecosystem processes; they are largely governed by growth regulatory compounds and influenced by environmental conditions. Yet, our knowledge about physiological drivers of root growth is mostly limited to laboratory‐based studies on model plant species.We sampled root tips of Eriophorum vaginatum and analyzed their auxin concentrations and meristem lengths biweekly over a growing season in situ in a subarctic peatland, both in surface soil and at the permafrost thawfront.Auxin concentrations were almost five times higher in surface than in thawfront soils and increased over the season, especially at the thawfront. Surprisingly, meristem length showed an opposite pattern and was almost double in thawfront compared with surface soils. Meristem length increased from peak to late season in the surface soils but decreased at the thawfront.Our study of in situ seasonal dynamics in root physiological parameters illustrates the potential for physiological methods to be applied in ecological studies and emphasizes the importance of in situ measurements. The strong effect of root location and the unexpected opposite patterns of meristem length and auxin concentrations likely show that auxin actively governs root growth to ensure a high potential for nutrient uptake at the thawfront. [ABSTRACT FROM AUTHOR]

In many plant species, petal abscission can be considered the final step of petal senescence. Cytokinins (CKs) are powerful suppressors of petal senescence; however, their role in petal abscission is ambiguous. Here, we observed that, in rose (Rosa hybrida), biologically active CK is accumulated during petal abscission and acts as an accelerator of the abscission process. Using a combination of reverse genetics, and molecular and biochemical techniques, we explored the roles of a LESION SIMULATING DISEASE1 (LSD1) family member RhLOL1 interacting with a bHLH transcription factor RhILR3 in CK-induced petal abscission. Silencing RhLOL1 delays rose petal abscission, while the overexpression of its ortholog SlLOL1 in tomato (Solanum lycopersicum) promotes pedicel abscission, indicating the conserved function of LOL1 in activating plant floral organ abscission. In addition, we identify a bHLH transcription factor, RhILR3, that interacts with RhLOL1. We show that RhILR3 binds to the promoters of the auxin signaling repressor auxin/indole-3-acetic acid (Aux/IAA) genes to inhibit their expression; however, the interaction of RhLOL1 with RhILR3 activates the expression of the Aux/IAA genes including RhIAA4-1. Silencing RhIAA4-1 delays rose petal abscission. Our results thus reveal a RhLOL1-RhILR3 regulatory module involved in CK-induced petal abscission via the regulation of the expression of the Aux/IAA genes.

Summary: Gibberellins (GA) have a profound influence on the formation of lateral root organs. However, the precise role this hormone plays in the cell‐specific events during lateral root formation, rhizobial infection and nodule organogenesis, including interactions with auxin and cytokinin (CK), is not clear.We performed epidermal‐ and endodermal‐specific complementation of the severely GA‐deficient na pea (Pisum sativum) mutant with Agrobacterium rhizogenes. Gibberellin mutants were used to examine the spatial expression pattern of CK (TCSn)‐ and auxin (DR5)‐responsive promoters and hormone levels.We found that GA produced in the endodermis promote lateral root and nodule organogenesis and can induce a mobile signal(s) that suppresses rhizobial infection. By contrast, epidermal‐derived GA suppress infection but have little influence on root or nodule development. GA suppress the CK‐responsive TCSn promoter in the cortex and are required for normal auxin activation during nodule primordia formation.Our findings indicate that GA regulate the checkpoints between infection thread (IT) penetration of the cortex and invasion of nodule primordial cells and promote the subsequent progression of nodule development. It appears that GA limit the progression and branching of IT in the cortex by restricting CK response and activate auxin response to promote nodule primordia development. [ABSTRACT FROM AUTHOR]

Summary: The nuclear TIR1/AFB‐Aux/IAA auxin pathway plays a crucial role in regulating plant growth and development. Specifically, the IAA17/AXR3 protein participates in Arabidopsis thaliana root development, response to auxin and gravitropism. However, the mechanism by which AXR3 regulates cell elongation is not fully understood.We combined genetical and cell biological tools with transcriptomics and determination of auxin levels and employed live cell imaging and image analysis to address how the auxin response pathways influence the dynamics of root growth.We revealed that manipulations of the TIR1/AFB‐Aux/IAA pathway rapidly modulate root cell elongation. While inducible overexpression of the AXR3‐1 transcriptional inhibitor accelerated growth, overexpression of the dominant activator form of ARF5/MONOPTEROS inhibited growth. In parallel, AXR3‐1 expression caused loss of auxin sensitivity, leading to transcriptional reprogramming, phytohormone signaling imbalance and increased levels of auxin. Furthermore, we demonstrated that AXR3‐1 specifically perturbs nuclear auxin signaling, while the rapid auxin response remains functional.Our results shed light on the interplay between the nuclear and cytoplasmic auxin pathways in roots, revealing their partial independence but also the dominant role of the nuclear auxin pathway during the gravitropic response of Arabidopsis thaliana roots. [ABSTRACT FROM AUTHOR]

Summary: Lignin contributes to plant mechanical properties during bending loads. Meanwhile, phytohormone auxin controls various plant biological processes. However, the mechanism of auxin's role in bending‐induced lignin biosynthesis was unclear, especially in bamboo, celebrated for its excellent deformation stability.Here, we reported that auxin response factors (ARF) 3 and ARF6 from Moso bamboo (Phyllostachys edulis (Carrière) J. Houz) directly regulate lignin biosynthesis pathway genes, and affect lignin biosynthesis in bamboo.Auxin and lignin exhibited asymmetric distribution patterns, and auxin promoted lignin biosynthesis in response to bending loads in bamboo. Employing transcriptomic and weighted gene co‐expression network analysis approach, we discovered that expression patterns of ARF3 and ARF6 strongly correlated with lignin biosynthesis genes. ARF3 and ARF6 directly bind to the promoter regions of 4‐coumarate: coenzyme A ligase (4CL3, 4CL7, and 4CL9) or caffeoyl‐CoA O‐methyltransferase (CCoAOMT2) genes, pivotal to lignin biosynthesis, and activate their expressions. Notably, the efficacy of this binding hinges on auxin levels. Alternation of the expressions of ARF3 and ARF6 substantially altered lignin accumulation in transgenic bamboo.Collectively, our study shed light on bamboo lignification genetics. Auxin signaling could directly modulate lignin biosynthesis genes to impact plant lignin content. [ABSTRACT FROM AUTHOR]

Summary: The locular gel, produced by the placenta, is important for fruit flavor and seed development in tomato. However, the mechanism underlying locule and placenta development is not fully understood yet.Here, we show that two SlARF transcription factors, SlARF8B and SlARF8A (SlARF8A/B), promote the development of locular and placenta tissues. The expression of both SlARF8A and SlARF8B is repressed by sly‐microRNA167 (sly‐miR167), allowing for the activation of auxin downstream genes.In slarf8a, slarf8b, and slarf8a/b mutants, the auxin (IAA) levels are decreased, whereas the levels of inactive IAA conjugates including IAA‐Ala, IAA‐Asp, and IAA‐Glu are increased. We further find that SlARF8B directly inhibits the expression of SlGH3.4, an acyl acid amino synthetase that conjugates the amino acids to IAA. Disruption of such auxin balance by the increased expression of SlGH3.4 or SlGH3.2 results in defective locular and placental tissues.Taken together, our findings reveal an important regulatory module constituted by sly‐miR167‐SlARF8A/B‐SlGH3.4 during the development of locular and placenta tissues of tomato fruits. [ABSTRACT FROM AUTHOR]

Summary: Auxin signaling provides a promising approach to controlling root system architecture and improving stress tolerance in plants. However, how the auxin signaling is transducted in this process remains unclear.The Aux indole‐3‐acetic acid (IAA) repressor IAA17.1 is stabilized by salinity, and primarily expressed in the lateral root (LR) primordia and tips in poplar. Overexpression of the auxin‐resistant form of IAA17.1 (IAA17.1m) led to growth inhibition of LRs, markedly reduced salt tolerance, increased reactive oxygen species (ROS) levels, and decreased flavonol content. We further identified that IAA17.1 can interact with the heat shock protein HSFA5a, which was highly expressed in roots and induced by salt stress. Overexpression of HSFA5a significantly increased flavonol content, reduced ROS accumulation, enhanced LR growth and salt tolerance in transgenic poplar. Moreover, HSFA5a could rescue the defective phenotypes caused by IAA17.1m.Expression analysis showed that genes associated with flavonol biosynthesis were altered in IAA17.1m‐ and HAFA5a‐overexpressing plants. Furthermore, we identified that HSFA5a directly activated the expression of key enzyme genes in the flavonol biosynthesis pathway, while IAA17.1 suppressed HSFA5a‐mediated activation of these genes.Collectively, the IAA17.1/HSFA5a module regulates flavonol biosynthesis, controls ROS accumulation, thereby modulating the root system of poplar to adapt to salt stress. [ABSTRACT FROM AUTHOR]

Summary: Lateral root (LR) positioning and development rely on the dynamic interplay between auxin production, transport but also inactivation. Nonetheless, how the latter affects LR organogenesis remains largely uninvestigated.Here, we systematically analyze the impact of the major auxin inactivation pathway defined by GRETCHEN HAGEN3‐type (GH3) auxin conjugating enzymes and DIOXYGENASE FOR AUXIN OXIDATION1 (DAO1) in all stages of LR development using reporters, genetics and inhibitors in Arabidopsis thaliana.Our data demonstrate that the gh3.1/2/3/4/5/6 hextuple (gh3hex) mutants display a higher LR density due to increased LR initiation and faster LR developmental progression, acting epistatically over dao1‐1. Grafting and local inhibitor applications reveal that root and shoot GH3 activities control LR formation. The faster LR development in gh3hex is associated with GH3 expression domains in and around developing LRs. The increase in LR initiation is associated with accelerated auxin response oscillations coinciding with increases in apical meristem size and LR cap cell death rates.Our research reveals how GH3‐mediated auxin inactivation attenuates LR development. Local GH3 expression in LR primordia attenuates development and emergence, whereas GH3 effects on pre‐initiation stages are indirect, by modulating meristem activities that in turn coordinate root growth with LR spacing. [ABSTRACT FROM AUTHOR]

Summary: Upon exposure to light, etiolated Arabidopsis seedlings form adventitious roots (AR) along the hypocotyl. While processes underlying lateral root formation are studied intensively, comparatively little is known about the molecular processes involved in the initiation of hypocotyl AR.AR and LR formation were studied using a small molecule named Hypocotyl Specific Adventitious Root INducer (HYSPARIN) that strongly induces AR but not LR formation. HYSPARIN does not trigger rapid DR5‐reporter activation, DII‐Venus degradation or Ca2+ signalling. Transcriptome analysis, auxin signalling reporter lines and mutants show that HYSPARIN AR induction involves nuclear TIR1/AFB and plasma membrane TMK auxin signalling, as well as multiple downstream LR development genes (SHY2/IAA3, PUCHI, MAKR4 and GATA23).Comparison of the AR and LR induction transcriptome identified SAURs, AGC kinases and OFP transcription factors as specifically upregulated by HYSPARIN. Members of the SAUR19 subfamily, OFP4 and AGC2 suppress HYS‐induced AR formation. While SAUR19 and OFP subfamily members also mildly modulate LR formation, AGC2 regulates only AR induction.Analysis of HYSPARIN‐induced AR formation uncovers an evolutionary conservation of auxin signalling controlling LR and AR induction in Arabidopsis seedlings and identifies SAUR19, OFP4 and AGC2 kinase as novel regulators of AR formation. [ABSTRACT FROM AUTHOR]

Summary: In the current genomic era, the search and deployment of new semi‐dwarf alleles have continued to develop better plant types in all cereals. We characterized an agronomically optimal semi‐dwarf mutation in Zea mays L. and a parallel polymorphism in Sorghum bicolor L.We cloned the maize brachytic1 (br1‐Mu) allele by a modified PCR‐based Sequence Amplified Insertion Flanking Fragment (SAIFF) approach. Histology and RNA‐Seq elucidated the mechanism of semi‐dwarfism. GWAS linked a sorghum plant height QTL with the Br1 homolog by resequencing a West African sorghum landraces panel.The semi‐dwarf br1‐Mu allele encodes an MYB transcription factor78 that positively regulates stalk cell elongation by interacting with the polar auxin pathway. Semi‐dwarfism is due to differential splicing and low functional Br1 wild‐type transcript expression. The sorghum ortholog, SbBr1, co‐segregates with the major plant height QTL qHT7.1 and is alternatively spliced. The high frequency of the Sbbr1 allele in African landraces suggests that African smallholder farmers used the semi‐dwarf allele to improve plant height in sorghum long before efforts to introduce Green Revolution‐style varieties in the 1960s.Surprisingly, variants for differential splicing of Brachytic1 were found in both commercial maize and smallholder sorghum, suggesting parallel tuning of plant architecture across these systems. [ABSTRACT FROM AUTHOR]

Summary: Abscission is predetermined in specialized cell layers called the abscission zone (AZ) and activated by developmental or environmental signals. In the grass family, most identified AZ genes regulate AZ anatomy, which differs among lineages. A YABBY transcription factor, SHATTERING1 (SH1), is a domestication gene regulating abscission in multiple cereals, including rice and Setaria. In rice, SH1 inhibits lignification specifically in the AZ. However, the AZ of Setaria is nonlignified throughout, raising the question of how SH1 functions in species without lignification.Crispr‐Cas9 knockout mutants of SH1 were generated in Setaria viridis and characterized with histology, cell wall and auxin immunofluorescence, transmission electron microscopy, hormonal treatment and RNA‐Seq analysis.The sh1 mutant lacks shattering, as expected. No differences in cell anatomy or cell wall components including lignin were observed between sh1 and the wild‐type (WT) until abscission occurs. Chloroplasts degenerated in the AZ of WT before abscission, but degeneration was suppressed by auxin treatment. Auxin distribution and expression of auxin‐related genes differed between WT and sh1, with the signal of an antibody to auxin detected in the sh1 chloroplast.SH1 in Setaria is required for activation of abscission through auxin signaling, which is not reported in other grass species. [ABSTRACT FROM AUTHOR]

Summary: The 3′,5′‐cyclic adenosine monophosphate (cAMP) is a versatile second messenger in many mammalian signaling pathways. However, its role in plants remains not well‐recognized. Recent discovery of adenylate cyclase (AC) activity for transport inhibitor response 1/auxin‐signaling F‐box proteins (TIR1/AFB) auxin receptors and the demonstration of its importance for canonical auxin signaling put plant cAMP research back into spotlight. This insight briefly summarizes the well‐established cAMP signaling pathways in mammalian cells and describes the turbulent and controversial history of plant cAMP research highlighting the major progress and the unresolved points. We also briefly review the current paradigm of auxin signaling to provide a background for the discussion on the AC activity of TIR1/AFB auxin receptors and its potential role in transcriptional auxin signaling as well as impact of these discoveries on plant cAMP research in general. [ABSTRACT FROM AUTHOR]

Summary: Ascorbic acid (AsA) is a water‐soluble antioxidant that plays important roles in plant development and human health. Understanding the regulatory mechanism underlying AsA biosynthesis is imperative to the development of high AsA plants.In this study, we reveal that the auxin response factor SlARF4 transcriptionally inhibits SlMYB99, which subsequently modulates AsA accumulation via transcriptional activation of AsA biosynthesis genes GPP, GLDH, and DHAR. The auxin‐dependent transcriptional cascade of SlARF4‐SlMYB99‐GPP/GLDH/DHAR modulates AsA synthesis, while mitogen‐activated protein kinase SlMAPK8 not only phosphorylates SlMYB99, but also activates its transcriptional activity. Both SlMYB99 and SlMYB11 proteins physically interact with each other, thereby synergistically regulating AsA biosynthesis by upregulating the expression of GPP, GLDH, and DHAR genes.Collectively, these results demonstrate that auxin and abscisic acid antagonistically regulate AsA biosynthesis during development and drought tolerance in tomato via the SlMAPK8‐SlARF4‐SlMYB99/11 module.These findings provide new insights into the mechanism underlying phytohormone regulation of AsA biosynthesis and provide a theoretical basis for the future development of high AsA plants via molecular breeding. [ABSTRACT FROM AUTHOR]

Dior R. Kelley is a plant scientist whose research focuses on hormonal control of plant growth and development. She obtained her Bachelor's degree in Chemistry from the University of California Santa Cruz and her PhD in Plant Biology from the University of California at Davis. Dior has worked as a postdoctoral fellow at the Salk Institute for Biological Studies and the University of California San Diego. She is currently an Assistant Professor at Iowa State University. Dior's research involves studying the role of auxin in organ formation in maize and Arabidopsis thaliana. She has also served as an Associate Editor for the New Phytologist journal since 2023. [Extracted from the article]

Their results involve the CLV3 peptide as well as CLV1 and CLV2/CRN receptors that promote auxin-dependent primordium initiation, likely by inducing I YUCCA i auxin biosynthesis genes. Keywords: auxin; morphogenesis; plant development; regeneration; single-cell transcriptomics EN auxin morphogenesis plant development regeneration single-cell transcriptomics 1729 1731 3 11/06/23 20231201 NES 231201 After having spent over 2 years mostly online due to the COVID-19 outbreak, the Mechanism of Plant Development Conference 2022 renewed our ability to meet and engage in-person with fantastic scientists from across the field of plant development. Auxin, morphogenesis, plant development, regeneration, single-cell transcriptomics. [Extracted from the article]

Summary: Amino acid transporters are the principal mediators of organic nitrogen distribution within plants and are essential for plant growth and development. Despite this importance, relatively few amino acid transporter genes have been explored and elucidated in cucumber (Cucumis sativus).Here, a total of 86 amino acid transporter genes were identified in the cucumber genome. We further identified Amino Acid Permease (AAP) subfamily members that exhibited distinct expression patterns in different tissues.We found that the CsAAP2 as a candidate gene encoding a functional amino acid transporter is highly expressed in cucumber root vascular cells. CsAAP2 knockout lines exhibited arrested development of root meristem, which then caused the delayed initiation of lateral root and the inhibition of root elongation. What is more, the shoot growth of aap2 mutants was strongly retarded due to defects in cucumber root development.Moreover, aap2 mutants exhibited higher concentrations of amino acids and lignin in roots. We found that the mutant roots had a stronger ability to acidize medium. Furthermore, in the aap2 mutants, polar auxin transport was disrupted in the root tip, leading to high auxin levels in roots. Interestingly, slightly alkaline media rescued their severely reduced root growth by stimulating auxin pathway. [ABSTRACT FROM AUTHOR]

Keywords: Arabidopsis; auxin inactivation; conjugation; moss; oxidation; spruce EN Arabidopsis auxin inactivation conjugation moss oxidation spruce 2264 2270 7 05/23/23 20230615 NES 230615 Dynamic regulation of the concentration of the natural auxin indole-3-acetic acid (IAA) is essential to coordinate most physiological and developmental processes and responses to environmental changes (reviewed in Friml, [7]). A feeding experiment of moss WT gametophores with IAA, IAA-Glu, and oxIAA revealed that oxIAA-Glu mainly originated from oxidation of IAA-Glu (Dataset S2; Fig. Feeding spruce seedlings with IAA, IAA-Asp, IAA-Glu, and oxIAA showed that oxIAA-Asp and oxIAA-Glu accumulated predominantly after oxIAA treatment (Dataset S2; Fig. [Extracted from the article]

Summary: An environmentally responsive root system is crucial for plant growth and crop yield, especially in suboptimal soil conditions. This responsiveness enables the plant to exploit regions of high nutrient density while simultaneously minimizing abiotic stress. Despite the vital importance of root systems in regulating plant growth, significant gaps of knowledge exist in the mechanisms that regulate their architecture.Auxin defines both the frequency of lateral root (LR) initiation and the rate of LR outgrowth. Here, we describe a search for proteins that regulate root system architecture (RSA) by interacting directly with a key auxin transporter, PIN1. The native separation of Arabidopsis plasma membrane protein complexes identified several PIN1 co‐purifying proteins.Among them, AZG1 was subsequently confirmed as a PIN1 interactor. Here, we show that, in Arabidopsis, AZG1 is a cytokinin (CK) import protein that co‐localizes with and stabilizes PIN1, linking auxin and CK transport streams. AZG1 expression in LR primordia is sensitive to NaCl, and the frequency of LRs is AZG1‐dependent under salt stress.This report therefore identifies a potential point for auxin:cytokinin crosstalk, which shapes RSA in response to NaCl. [ABSTRACT FROM AUTHOR]

Summary: The root system architecture in plants is a result of multiple evolutionary innovations over time in response to changing environmental cues. Dichotomy and endogenous lateral branching in the roots evolved in lycophytes lineage but extant seed plants use lateral branching instead. This has led to the development of complex and adaptive root systems, with lateral roots playing a key role in this process exhibiting conserved and divergent features in different plant species. The study of lateral root branching in diverse plant species can shed light on the orderly yet distinct nature of postembryonic organogenesis in plants. This insight provides an overview of the diversity in lateral root (LR) development in various plant species during the evolution of root system in plants. [ABSTRACT FROM AUTHOR]

Summary: PIN‐FORMED auxin efflux transporters, a subclass of which is plasma membrane‐localised, mediate a variety of land‐plant developmental processes via their polar localisation and subsequent directional auxin transport. We provide the first characterisation of PIN proteins in liverworts using Marchantia polymorpha as a model system. Marchantia polymorpha possesses a single PIN‐FORMED gene, whose protein product is predicted to be plasma membrane‐localised, MpPIN1.To characterise MpPIN1, we created loss‐of‐function alleles and produced complementation lines in both M. polymorpha and Arabidopsis. In M. polymorpha, gene expression and protein localisation were tracked using an MpPIN1 transgene encoding a translationally fused fluorescent protein.Overexpression of MpPIN1 can partially complement loss of an orthologous gene, PIN‐FORMED1, in Arabidopsis. In M. polymorpha, MpPIN1 influences development in numerous ways throughout its life cycle. Most notably, MpPIN1 is required to establish gemmaling dorsiventral polarity and for orthotropic growth of gametangiophore stalks, where MpPIN1 is basally polarised.PIN activity is largely conserved within land plants, with PIN‐mediated auxin flow providing a flexible mechanism to organise growth. Specifically, PIN is fundamentally linked to orthotropism and to the establishment of de novo meristems, the latter potentially involving the formation of both auxin biosynthesis maxima and auxin‐signalling minima. [ABSTRACT FROM AUTHOR]

Summary: Auxin has long been known as an important regulator of plant growth and development. Classical studies in auxin biology have uncovered a 'canonical' transcriptional auxin‐signalling pathway involving the TRANSPORT INHIBITOR RESPONSE1/AUXIN SIGNALING F‐BOX (TIR1/AFB) receptors. TIR1/AFB perception of auxin triggers the degradation of repressors and the derepression of auxin‐responsive genes. Nevertheless, the canonical pathway cannot account for all aspects of auxin biology, such as physiological responses that are too rapid for transcriptional regulation. This Tansley insight will explore several 'non‐canonical' pathways that have been described in recent years mediating fast auxin responses. We focus on the interplay between a nontranscriptional branch of TIR1/AFB signalling and a TRANSMEMBRANE KINASE1 (TMK1)‐mediated pathway in root acid growth. Other developmental aspects involving the TMKs and their association with the controversial AUXIN‐BINDING PROTEIN 1 (ABP1) will be discussed. Finally, we provide an updated overview of the ETTIN (ETT)‐mediated pathway in contexts outside of gynoecium development. [ABSTRACT FROM AUTHOR]

Summary: A strong root system facilitates the absorption of water and nutrients from the soil, to improve the growth of crops. However, to date, there are still very few root development regulatory genes that can be used in crop breeding for agriculture.In this study, we cloned a negative regulator gene of root development, Robust Root System 1 (RRS1), which encodes an R2R3‐type MYB family transcription factor. RRS1 knockout plants showed enhanced root growth, including longer root length, longer lateral root length, and larger lateral root density. RRS1 represses root development by directly activating the expression of OsIAA3 which is involved in the auxin signaling pathway.A natural variation in the coding region of RRS1 changes the transcriptional activity of its protein. RRS1T allele, originating from wild rice, possibly increases root length by means of weakening regulation of OsIAA3.Knockout of RRS1 enhances drought resistance by promoting water absorption and improving water use efficiency. This study provides a new gene resource for improving root systems and cultivating drought‐resistant rice varieties with important values in agricultural applications. [ABSTRACT FROM AUTHOR]

Summary: Plant embryogenesis results from the fusion of male and female gametes but can also be induced in somatic cells. The molecular pathways for embryo initiation are poorly understood, especially in monocots. In rice, the male gamete expressed BABY BOOM1 (OsBBM1) transcription factor functions as an embryogenic trigger in the zygote and can also promote somatic embryogenesis when ectopically expressed in somatic tissues.We used gene editing, transcriptome profiling, and chromatin immunoprecipitation to determine the molecular players involved in embryo initiation downstream of OsBBM1.We identify OsYUCCA (OsYUC) auxin biosynthesis genes as direct targets of OsBBM1. Unexpectedly, these OsYUC targets in zygotes are expressed only from the maternal genome, whereas the paternal genome exclusively provides functional OsBBM1 to initiate embryogenesis. Induction of somatic embryogenesis by exogenous auxin requires OsBBM genes and downstream OsYUC targets. Ectopic OsBBM1 initiates somatic embryogenesis without exogenous auxins but requires functional OsYUC genes.Thus, an OsBBM‐OsYUC module is a key player for both somatic and zygotic embryogenesis in rice. Zygotic embryo initiation involves a partnership of male and female genomes, through which paternal OsBBM1 activates maternal OsYUC genes. In somatic embryogenesis, exogenous auxin triggers OsBBM1 expression, which then activates endogenous auxin biosynthesis OsYUC genes. [ABSTRACT FROM AUTHOR]

Summary: Root lodging poses a major threat to maize production, resulting in reduced grain yield and quality, and increased harvest costs.Here, we combined expressional, genetic, and cytological studies to demonstrate a role of ZmYUC2 and ZmYUC4 in regulating gravitropic response of the brace root and lodging resistance in maize.We show that both ZmYUC2 and ZmYUC4 are preferentially expressed in root tips with partially overlapping expression patterns, and the protein products of ZmYUC2 and ZmYUC4 are localized in the cytoplasm and endoplasmic reticulum, respectively. The Zmyuc4 single mutant and Zmyuc2/4 double mutant exhibit enlarged brace root angle compared with the wild‐type plants, with larger brace root angle being observed in the Zmyuc2/4 double mutant. Consistently, the brace root tips of the Zmyuc4 single mutant and Zmyuc2/4 double mutant accumulate less auxin and are defective in proper reallocation of auxin in response to gravi‐stimuli. Furthermore, we show that the Zmyuc4 single mutant and the Zmyuc2/4 double mutant display obviously enhanced root lodging resistance.Our combined results demonstrate that ZmYUC2‐ and ZmYUC4‐mediated local auxin biosynthesis is required for normal gravity response of the brace roots and provide effective targets for breeding root lodging resistant maize cultivars. [ABSTRACT FROM AUTHOR]

Summary: Parallel veins are characteristic of monocots, including grasses (Poaceae). Therefore, how parallel veins develop as the leaf grows in the medial–lateral (ML) dimension is a key question in grass leaf development.Using fluorescent protein reporters, we mapped auxin, cytokinin (CK), and gibberellic acid (GA) response patterns in maize (Zea mays) leaf primordia. We further defined the roles of these hormones in ML growth and vein formation through combinatorial genetic analyses and measurement of hormone concentrations.We discovered a novel pattern of auxin response in the adaxial protoderm that we hypothesize has important implications for the orderly formation of 3° veins early in leaf development. In addition, we found an auxin transport and response pattern in the margins that correlate with the transition from ML to proximal–distal growth. We present evidence that auxin efflux precedes CK response in procambial strand development. We also determined that GA plays an early role in the shoot apical meristem as well as a later role in the primordium to restrict ML growth.We propose an integrative model whereby auxin regulates ML growth and vein formation in the maize leaf through control of GA and CK. [ABSTRACT FROM AUTHOR]

Summary: The auxin efflux PIN‐FORMED (PIN) proteins are conserved in all land plants and important players in plant development. In the moss Physcomitrella (Physcomitrium patens), three canonical PINs (PpPINA–C) are expressed in the leafy shoot (gametophore). PpPINA and PpPINB show functional activity in vegetative growth and sporophyte development. Here, we examined the role of PpPINC in the life cycle of Physcomitrella.We established reporter and knockout lines for PpPINC and analysed vegetative and reproductive tissues using microscopy and transcriptomic sequencing of moss gametangia.PpPINC is expressed in immature leaves, mature gametangia and during sporophyte development. The sperm cells (spermatozoids) of pinC knockout mutants exhibit increased motility and an altered flagella phenotype. Furthermore, the pinC mutants have a higher portion of differentially expressed genes related to spermatogenesis, increased fertility and an increased abortion rate of premeiotic sporophytes.Here, we show that PpPINC is important for spermatogenesis and sporophyte retention. We propose an evolutionary conserved way of polar growth during early moss embryo development and sporophyte attachment to the gametophore while suggesting the mechanical function in sporophyte retention of a ring structure, the Lorch ring. [ABSTRACT FROM AUTHOR]

Summary: Auxin phytohormone has a role in most aspects of the life of a land plant and is found even in ancient plants such as single‐cell green algae. Auxin's ubiquitous but specific effects have been mainly explained by the extraordinary ability of plants to interpret spatiotemporal patterns of auxin concentrations via the regulation of gene transcription. This is thought to be achieved through the combinatorial effects of two families of nuclear coreceptor proteins, that is the TRANSPORT INHIBITOR RESPONSE1 and AUXIN‐SIGNALING F‐BOX (TIR1/AFB) and AUXIN/INDOLE ACETIC ACID. Recent evidence has suggested transcription‐independent roles of TIR1/AFBs localized outside the nucleus and TRANSMEMBRANE KINASE (TMK)‐based auxin signaling occurring in the plasma membrane. Furthermore, emerging evidence supports a coordinated action of the intra‐ and extranuclear auxin signaling pathways to regulate specific auxin responses. Here, we highlight how auxin signaling acts inside and outside the nucleus for the regulation of growth and morphogenesis and propose that the future direction of auxin biology lies in the elucidation of a new collaborative paradigm of intra‐ and extranuclear auxin signaling. [ABSTRACT FROM AUTHOR]

Summary: Leaves are strikingly diverse in terms of shapes and complexity. The wild and cultivated strawberry plants mostly develop trifoliate compound leaves, yet the underlying genetic basis remains unclear in this important fruit crop in Rosaceae.Here, we identified two EMS mutants designated simple leaf1 (sl1‐1 and sl1‐2) and one natural simple‐leafed mutant monophylla in Fragaria vesca. Their causative mutations all reside in SL1 (FvH4_7g28640) causing premature stop codon at different positions in sl1‐1 and sl1‐2 and an eight‐nucleotide insertion (GTTCATCA) in monophylla.SL1 encodes a transcription regulator with the conserved DNA‐binding domain GT‐1 and the catalytic domain of protein kinases PKc. Expression of SL1pro::SL1 in sl1‐1 completely restored compound leaf formation. The 35S::SL1 lines developed palmate‐like leaves with four or five leaflets at a low penetrance. However, overexpressing the truncated SL1ΔPK caused no phenotypes, probably due to the disruption of homodimerization. SL1 is preferentially expressed at the tips of leaflets and serrations. Moreover, SL1 is closely associated with the auxin pathway and works synergistically with FveLFYa in leaf morphogenesis.Overall, our work uncovered a new type of transcription regulator that promotes compound leaf formation in the woodland strawberry and shed new lights on the diversity of leaf complexity control. [ABSTRACT FROM AUTHOR]

Summary: Plant root architecture plasticity in response to biotic stresses has not been thoroughly investigated. Infection by endoparasitic cyst nematodes induces root architectural changes that involve the formation of secondary roots at infection sites. However, the molecular mechanisms regulating secondary root formation in response to cyst nematode infection remain largely unknown.We first assessed whether secondary roots form in a nematode density‐dependent manner by challenging wild‐type Arabidopsis plants with increasing numbers of cyst nematodes (Heterodera schachtii). Next, using jasmonate‐related reporter lines and knockout mutants, we tested whether tissue damage by nematodes triggers jasmonate‐dependent secondary root formation. Finally, we verified whether damage‐induced secondary root formation depends on local auxin biosynthesis at nematode infection sites.Intracellular host invasion by H. schachtii triggers a transient local increase in jasmonates, which activates the expression of ERF109 in a COI1‐dependent manner. Knockout mutations in COI1 and ERF109 disrupt the nematode density‐dependent increase in secondary roots observed in wild‐type plants. Furthermore, ERF109 regulates secondary root formation upon H. schachtii infection via local auxin biosynthesis.Host invasion by H. schachtii triggers secondary root formation via the damage‐induced jasmonate‐dependent ERF109 pathway. This points at a novel mechanism underlying plant root plasticity in response to biotic stress. [ABSTRACT FROM AUTHOR]

Summary: Plants have a broad capacity to regenerate damaged organs. The study of wounding in multiple developmental systems has uncovered many of the molecular properties underlying plants' competence for regeneration at the local cellular level. However, in nature, wounding is rarely localized to one place, and plants need to coordinate regeneration responses at multiple tissues with environmental conditions and their physiological state. Here, we review the evidence for systemic signals that regulate regeneration on a plant‐wide level. We focus on the role of auxin and sugars as short‑ and long‐range signals in natural wounding contexts and discuss the varied origin of these signals in different regeneration scenarios. Together, this evidence calls for a broader, system‐wide view of plant regeneration competence. [ABSTRACT FROM AUTHOR]

Summary: Sulfur (S) is an essential macronutrient for plants and a signaling molecule in abiotic stress responses. It is known that S availability modulates root system architecture; however, the underlying molecular mechanisms are largely unknown.We previously reported an Arabidopsis gain‐of‐function mutant sulfate utilization efficiency4 (sue4) that could tolerate S deficiency during germination and early seedling growth with faster primary root elongation. Here, we report that SUE4, a novel plasma membrane‐localized protein, interacts with the polar auxin transporter PIN1, resulting in reduced PIN1 protein levels and thus decreasing auxin transport to the root tips, which promotes primary root elongation.Moreover, SUE4 is induced by sulfate deficiency, consistent with its role in root elongation. Further analyses showed that the SUE4–PIN1 interaction decreased PIN1 levels, possibly through 26 S proteasome‐mediated degradation.Taken together, our finding of SUE4‐mediated root elongation is consistent with root adaptation to highly mobile sulfate in soil, thus revealing a novel component in the adaptive response of roots to S deficiency. [ABSTRACT FROM AUTHOR]

Summary: Efficient root‐to‐shoot delivery of water and nutrients in plants relies on the correct differentiation of xylem cells into hollow elements. While auxin is integral to the formation of xylem cells, it remains poorly characterized how each subcellular pool of this hormone regulates this process.Combining genetic and cell biological approaches, we investigated the bipartite activity of nucleoplasmic vs plasma membrane‐associated phosphatidylinositol 4‐phosphate kinases PIP5K1 and its homolog PIP5K2 in Arabidopsis thaliana roots and uncovered a novel mechanism by which phosphoinositides integrate distinct aspects of the auxin signaling cascade and, in turn, regulate the onset of xylem differentiation.The appearance of undifferentiated cells in protoxylem strands of pip5k1 pip5k2 is phenomimicked in auxin transport and perception mutants and can be partially restored by the nuclear residence of PIP5K1. By contrast, exclusion of PIP5K1 from the nucleus hinders the auxin‐mediated induction of the xylem master regulator VASCULAR RELATED NAC DOMAIN (VND) 7. A xylem‐specific increase of auxin levels abolishes pip5k1 pip5k2 vascular defects, indicating that the establishment of auxin maxima is required to activate VND7‐mediated xylem differentiation.Our results describe a new mechanism by which distinct subcellular pools of phosphoinositides integrate auxin transport and perception to initiate xylem differentiation in a spatiotemporal manner. [ABSTRACT FROM AUTHOR]

Summary: The various combinations and regulations of different subunits of phosphatase PP2A holoenzymes underlie their functional complexity and importance. However, molecular mechanisms governing the assembly of PP2A complex in response to external or internal signals remain largely unknown, especially in Arabidopsis thaliana.We found that the phosphorylation status of Bβ of PP2A acts as a switch to regulate the activity of PP2A. In the absence of ethylene, phosphorylated Bβ leads to an inactivation of PP2A; the substrate EIR1 remains to be phosphorylated, preventing the EIR1‐mediated auxin transport in epidermis, leading to normal root growth.Upon ethylene treatment, the dephosphorylated Bβ mediates the formation of the A2–C4–Bβ protein complex to activate PP2A, resulting in the dephosphorylation of EIR1 to promote auxin transport in epidermis of elongation zone, leading to root growth inhibition.Altogether, our research revealed a novel molecular mechanism by which the dephosphorylation of Bβ subunit switches on PP2A activity to dephosphorylate EIR1 to establish EIR1‐mediated auxin transport in the epidermis in elongation zone for root growth inhibition in response to ethylene. [ABSTRACT FROM AUTHOR]

Summary: Auxin is a critical phytohormone that is involved in the regulation of most plant growth and developmental responses. In particular, epigenetic mechanisms, like histone modifications and DNA methylation, were reported to affect auxin biosynthesis and transport. However, the involvement of other epigenetic factors, such as histone variant H2A.Z, in the auxin‐related developmental regulation remains unclear.We report that the histone variant H2A.Z knockdown mutant in Arabidopsis Col‐0 ecotype, h2a.z‐kd, has more lateral roots and weak gravitational responses related to auxin‐regulated growth performances. Further study revealed that auxin promotes the eviction of H2A.Z from the auxin‐responsive genes SMALL AUXIN‐UP RNAs (SAURs) to activate their transcriptions.We found that IAA promotes the transcription of H2A.Z genes through HOMEOBOX PROTEIN 22/25 (AtHB22/25) transcription factors which work as downstream targets of ARF7/19 in auxin signaling. Double mutant of hb22 hb25 showed similar lateral root and gravitropism phenotypes to h2a.z‐kd.Our results shed light on a reciprocal regulation hub through INOSITOL AUXOTROPHY 80‐mediated H2A.Z eviction and ARF7/19‐HB22/25‐mediated H2A.Z transcription to modulate the activation of SAURs and plant growth in Arabidopsis. [ABSTRACT FROM AUTHOR]

Summary: Shade affects all aspects of plant growth and development, including seed germination, hypocotyl elongation, petiole growth, leaf hyponasty, and flowering time. Here, we found that mutations in the key Arabidopsis karrikins signal perception‐associated KARRIKIN INSENSITIVE 2 (KAI2) gene, encoding an α/β‐fold hydrolase, and the MORE AXILLARY GROWTH 2 (MAX2) gene, encoding an F‐box protein, led to greater hypocotyl elongation under shade avoidance conditions.We further verified that these phenotypes were caused by perception of the endogenous KAI2‐ligands (KLs), and that this phenotype is independent of strigolactone biosynthetic or signaling pathways. Upon perception of a KL, it is probable that the target protein forms a complex with the KAI2/MAX2 proteins, which are degraded through the action of the 26S proteasome.We demonstrated that SUPPRESSOR OF MAX2‐1 (SMAX1) is the degradation target for the KAI2/MAX2 complex in the context of shade avoidance. KAI2 and MAX2 require SMAX1 to limit the hypocotyl growth associated with shade avoidance. Treatment with l‐kynurenine, an inhibitor of auxin accumulation, partially restored elongation of kai2 mutant hypocotyls under simulated shade. Furthermore, KAI2 is involved in regulating auxin accumulation and polar auxin transport, which may contribute to the hypocotyl shade response.In addition, SMAX1 gene overexpression promoted the hypocotyl shade response. RNA‐sequencing analysis revealed that SMAX1‐overexpression affected the expression of many auxin homeostasis genes, especially under simulated shade. Altogether, our data support the conclusion that KL signaling regulates shade avoidance by modulating auxin homeostasis in the hypocotyl. [ABSTRACT FROM AUTHOR]

Summary: Plant biotrophic pathogens employ secreted molecules, called effectors, to suppress the host immune system and redirect the host's metabolism and development in their favour. Putative effectors of the gall‐inducing maize pathogenic fungus Ustilago maydis were analysed for their ability to induce auxin signalling in plants.Using genetic, biochemical, cell‐biological, and bioinformatic approaches we functionally elucidate a set of five, genetically linked effectors, called Topless (TPL) interacting protein (Tips) effectors that induce auxin signalling.We show that Tips induce auxin signalling by interfering with central corepressors of the TPL family. CRISPR‐Cas9 mutants and deletion strain analysis indicate that the auxin signalling inducing subcluster effectors plays a redundant role in virulence.Although none of the Tips seem to have a conserved interaction motif, four of them bind solely to the N‐terminal TPL domain and, for Tip1 and Tip4, we demonstrate direct competition with auxin/indole‐3‐acetic acid transcriptional repressors for their binding to TPL class of corepressors. Our findings reveal that TPL proteins, key regulators of growth–defence antagonism, are a major target of the U. maydis effectome. [ABSTRACT FROM AUTHOR]

Targeted cellular auxin distribution is required for morphogenesis and adaptive responses of plant organs. In Arabidopsis thaliana (Arabidopsis), this involves the prototypical auxin influx facilitator AUX1 and its LIKE-AUX1 (LAX) homologs, which act partially redundantly in various developmental processes. Interestingly, AUX1 and its homologs are not strictly essential for the Arabidopsis life cycle. Indeed, aux1 lax1 lax2 lax3 quadruple knock-outs are mostly viable and fertile, and strong phenotypes are only observed at low penetrance. Here we investigated the Brachypodium distachyon (Brachypodium) AUX1 homolog BdAUX1 by genetic, cell biological and physiological analyses. We report that BdAUX1 is essential for Brachypodium development. Bdaux1 loss-of-function mutants are dwarfs with aberrant flower development, and consequently infertile. Moreover, they display a counter-intuitive root phenotype. Although Bdaux1 roots are agravitropic as expected, in contrast to Arabidopsis aux1 mutants they are dramatically longer than wild type roots because of exaggerated cell elongation. Interestingly, this correlates with higher free auxin content in Bdaux1 roots. Consistently, their cell wall characteristics and transcriptome signature largely phenocopy other Brachypodium mutants with increased root auxin content. Our results imply fundamentally different wiring of auxin transport in Brachypodium roots and reveal an essential role of BdAUX1 in a broad spectrum of developmental processes, suggesting a central role for AUX1 in pooideae.

Strigolactones (SLs) are carotenoid-derived phytohormones shaping plant architecture and inducing the symbiosis with endomycorrhizal fungi. In Petunia hybrida, SL transport within the plant and towards the rhizosphere is driven by the ABCG-class protein PDR1. PDR1 expression is regulated by phytohormones and by the soil phosphate abundance, and thus SL transport integrates plant development with nutrient conditions. We overexpressed PDR1 (PDR1 OE) to investigate whether increased endogenous SL transport is sufficient to improve plant nutrition and productivity. Phosphorus quantification and nondestructive X-ray computed tomography were applied. Morphological and gene expression changes were quantified at cellular and whole tissue levels via time-lapse microscopy and quantitative PCR. PDR1 OE significantly enhanced phosphate uptake and plant biomass production on phosphate-poor soils. PDR1 OE plants showed increased lateral root formation, extended root hair elongation, faster mycorrhization and reduced leaf senescence. PDR1 overexpression allowed considerable SL biosynthesis by releasing SL biosynthetic genes from an SL-dependent negative feedback. The increased endogenous SL transport/biosynthesis in PDR1 OE plants is a powerful tool to improve plant growth on phosphate-poor soils. We propose PDR1 as an as yet unexplored trait to be investigated for crop production. The overexpression of PDR1 is a valuable strategy to investigate SL functions and transport routes.