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Axillary meristems (AMs) give rise to lateral shoots and are critical to plant architecture. Understanding how developmental cues and environmental signals impact AM development will enable the improvement of plant architecture in agriculture. Here, we show that ARGONAUTE10 (AGO10), which sequesters miR165/166, promotes AM development through the miR165/166 target gene REVOLUTA. We reveal that AGO10 expression is precisely controlled temporally and spatially by auxin, brassinosteroids, and light to result in AM initiation only in the axils of leaves at a certain age. AUXIN RESPONSE FACTOR 5 (ARF5) activates while BRASSINAZOLE-RESISTANT 1 (BZR1) and PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) repress AGO10 transcription directly. In axils of young leaves, BZR1 and PIF4 repress AGO10 expression to prevent AM initiation. In axils of older leaves, ARF5 upregulates AGO10 expression to promote AM initiation. Our results uncover the spatiotemporal control of AM development through the cooperation of hormones and light converging on a regulator of microRNA.

Multi-pistil trait in wheat is of great potential value in plant development research and crop breeding. Our previous studies identified the Pis1 locus that causes three pistils in wheat by genetic mapping using multiple DNA marker systems. However, there are still 26 candidate genes on the locus, and the causal gene remains to be found. In this study, we aimed to approach the molecular mechanism of multi-pistil formation. Comparative RNA sequencing (RNA-Seq) during the pistil formation was undertaken in four wheat lines: a three-pistil mutant TP, a single-pistil TILLING mutant of TP (SP), a three-pistil near-isogenic line CM28TP with the background of cultivar Chunmai 28 (CM28), and CM28. Electron microscopic analysis specified probable developmental stages of young spikes for the three-pistil formation. mRNA sequencing in the young spikes of the four lines represented 253 down-regulated genes and 98 up-regulated genes in both three-pistil lines, which included six potential genes for ovary development. Weighted gene co-expression analysis represented three-pistil trait-associated transcription factor-like genes, among which one hub gene, ARF5, was the most highlighted. ARF5 is on the Pis1 locus and an orthologue of MONOPTEROS which mediates tissue development in Arabidopsis. qRT-PCR validation implies that the deficiency of ARF5 underlies the three-pistil formation in wheat. [ABSTRACT FROM AUTHOR]

Light is an environmental signaling, whereas Aux/IAA proteins and Auxin Response Factors (ARFs) are regulators of auxin signalling. Aux/IAA proteins are unstable, and their degradation dependents on 26S ubiquitin-proteasome and is promoted by Auxin. Auxin binds directly to a SCF-type ubiquitin-protein ligase, TIR1, facilitates the interaction between Aux/IAA proteins and TIR1, and then the degradation of Aux/IAA proteins. A few studies have reported that some ARFs are also unstable proteins, and their degradation is also mediated by 26S proteasome. In this study, by using of antibodies recognizing endogenous ARF7 proteins, we found that protein stability of ARF7 was affected by light. By expressing MYC tagged ARF activators in protoplasts, we found that degradation of ARF7 was inhibited by 26 proteasome inhibitors. In addition, at least ARF5 and ARF19 were also unstable proteins, and degradation of ARF5 via 26S proteasome was further confirmed by using stable transformed plants overexpressing ARF5 with a GUS tag [ABSTRACT FROM AUTHOR]

Summary: Optimal root system architecture is beneficial for water‐fertilizer use efficiency, stress tolerance and yield improvement of crops. However, because of the complexity of root traits and difficulty in phenotyping deep roots, the study on mechanisms of root development is rarely reported in wheat (Triticum aestivum L.). In this study, we identified that the LBD (LATERAL ORGAN BOUNDARIES DOMAIN) gene TaMOR (MORE ROOT in wheat) determines wheat crown root initiation. The mor mutants exhibited less or even no crown root, dwarfism, less grain number and lodging caused by few roots. The observation of cross sections showed that crown root initiation is inhibited in the mor mutants. Molecular assays revealed that TaMOR interacts with the auxin response factor ARF5 to directly induce the expression of the auxin transporter gene PIN2 (PIN‐FORMED 2) in the root base to regulate crown root initiation. In addition, a 159‐bp MITE (miniature inverted‐repeat transposable element) insertion causing DNA methylation and lower expression of TaMOR‐B was identified in TaMOR‐B promoter, which is associated with lower root dry weight and shorter plant height. The results bring new light into regulation mechanisms of crown root initiation and offer a new target for the improvement of root system architecture in wheat. [ABSTRACT FROM AUTHOR]

Summary: The gaseous plant hormone ethylene induces the ripening of climacteric fruit, including apple (Malus domestica). Another phytohormone, auxin, is known to promote ethylene production in many horticultural crops, but the regulatory mechanism remains unclear.Here, we found that auxin application induces ethylene production in apple fruit before the stage of commercial harvest, when they are not otherwise capable of ripening naturally.The expression of MdARF5, a member of the auxin response factor transcription factor (TF) family involved in the auxin signaling pathway, was enhanced by treatment with the synthetic auxin naphthaleneacetic acid (NAA). Further studies revealed that MdARF5 binds to the promoter of MdERF2, encoding a TF in the ethylene signaling pathway, as well as the promoters of two 1‐aminocyclopropane‐1‐carboxylic acid synthase (ACS) genes (MdACS3a and MdACS1) and an ACC oxidase (ACO) gene, MdACO1, all of which encode key steps in ethylene biosynthesis, thereby inducing their expression. We also observed that auxin‐induced ethylene production was dependent on the methylation of the MdACS3a promoter.Our findings reveal that auxin induces ethylene biosynthesis in apple fruit through activation of MdARF5 expression. [ABSTRACT FROM AUTHOR]

Summary: Wood development is strictly regulated by various phytohormones and auxin plays a central regulatory role in this process. However, how the auxin signaling is transducted in developing secondary xylem during wood formation in tree species remains unclear.Here, we identified an Aux/INDOLE‐3‐ACETIC ACID 9 (IAA9)‐AUXIN RESPONSE FACTOR 5 (ARF5) module in Populus tomentosa as a key mediator of auxin signaling to control early developing xylem development.PtoIAA9, a canonical Aux/IAA gene, is predominantly expressed in vascular cambium and developing secondary xylem and induced by exogenous auxin. Overexpression of PtoIAA9m encoding a stabilized IAA9 protein significantly represses secondary xylem development in transgenic poplar. We further showed that PtoIAA9 interacts with PtoARF5 homologs via the C‐terminal III/IV domains. The truncated PtoARF5.1 protein without the III/IV domains rescued defective phenotypes caused by PtoIAA9m. Expression analysis showed that the PtoIAA9‐PtoARF5 module regulated the expression of genes associated with secondary vascular development in PtoIAA9m‐ and PtoARF5.1‐overexpressing plants. Furthermore, PtoARF5.1 could bind to the promoters of two Class III homeodomain‐leucine zipper (HD‐ZIP III) genes, PtoHB7 and PtoHB8, to modulate secondary xylem formation.Taken together, our results suggest that the Aux/IAA9‐ARF5 module is required for auxin signaling to regulate wood formation via orchestrating the expression of HD‐ZIP III transcription factors in poplar. [ABSTRACT FROM AUTHOR]

Auxin regulates nearly all aspects of plant growth and development including cell division, cell elongation and cell differentiation, which are achieved largely by rapid regulation of auxin response genes. However, the functions of a large number of auxin response genes remain uncharacterized. Paclobutrazol Resistance (PRE) proteins are non-DNA binding basic helix-loop-helix transcription factors that have been shown to be involved in gibberellin and brassinosteroid signaling, and light responses in Arabidopsis. Here, we provide molecular and genetic evidence that PRE6, one of the six PRE genes in Arabidopsis, is an auxin response gene, and that PRE6 is involved in the regulation of auxin signaling. By using quantitative RT-PCR, we showed that the expression level of PRE6 was increased in response to exogenously applied IAA. GUS staining results also showed that the expression of GUS reporter gene in the PRE6p:GUS transgenic seedlings was elevated in response to auxin. Phenotypic analysis showed that overexpression of PRE6 in Arabidopsis resulted in auxin-related phenotypes including elongated hypocotyl and primary roots, and reduced number of lateral roots when compared with the Col wild type seedlings, whereas opposite phenotypes were observed in the pre6 mutants. Further analysis showed that PRE6 overexpression plants were hyposensitive, whereas pre6 mutants were hypersensitive to auxin in root and hypocotyl elongation and lateral root formation assays. By using protoplasts transfection, we showed that PRE6 functions as a transcriptional repressor. Consistent with this, the expression of the auxin response reporter DR5:GUS was decreased in PRE6 overexpression lines, but increased in pre6 mutants. When co-transfected into protoplasts, ARF5 and ARF8 activated the expression of the PRE6p:GUS reporter. Chromatin immunoprecipitation assays showed that ARF5 and ARF8 can be recruited to the promoter regions of PRE6. Taken together, these results suggest that PRE6 is an auxin response gene whose expression is directly regulated by ARF5 and ARF8, and that PRE6 is a transcriptional repressor that negatively regulates auxin responses in Arabidopsis.

Key message: Extensive modulation of numerous ARF transcripts in the embryogenic culture of Arabidopsis indicates a substantial role of auxin signaling in the mechanism of somatic embryogenesis induction. Abstract: Somatic embryogenesis (SE) is induced by auxin in plants and auxin signaling is considered to play a key role in the molecular mechanism that controls the embryogenic transition of plant somatic cells. Accordingly, the expression of AUXIN RESPONSE FACTOR ( ARF) genes in embryogenic culture of Arabidopsis was analyzed. The study revealed that 14 of the 22 ARFs were transcribed during SE in Arabidopsis. RT-qPCR analysis indicated that the expression of six ARFs ( ARF5, ARF6, ARF8, ARF10, ARF16, and ARF17) was significantly up-regulated, whereas five other genes ( ARF1, ARF2, ARF3, ARF11, and ARF18) were substantially down-regulated in the SE-induced explants. The activity of ARFs during SE was also monitored with GFP reporter lines and the ARFs that were expressed in areas of the explants engaged in SE induction were detected. A functional test of ARFs transcribed during SE was performed and the embryogenic potential of the arf mutants and overexpressor lines was evaluated. ARFs with a significantly modulated expression during SE coupled with an impaired embryogenic response of the relevant mutant and/or overexpressor line, including ARF1, ARF2, ARF3, ARF5, ARF6, ARF8, and ARF11 were indicated as possibly being involved in SE induction. The study provides evidence that embryogenic induction strongly depends on ARFs, which are key regulators of the auxin signaling. Some clues on the possible functions of the candidate ARFs, especially ARF5, in the mechanism of embryogenic transition are discussed. The results provide guidelines for further research on the auxin-related functional genomics of SE and the developmental plasticity of somatic cells. [ABSTRACT FROM AUTHOR]

Summary The periodic formation of plant organs such as leaves and flowers gives rise to intricate patterns that have fascinated biologists and mathematicians alike for hundreds of years [ 1 ]. The plant hormone auxin plays a central role in establishing these patterns by promoting organ formation at sites where it accumulates due to its polar, cell-to-cell transport [ 2–6 ]. Although experimental evidence as well as modeling suggest that feedback from auxin to its transport direction may help specify phyllotactic patterns [ 7–12 ], the nature of this feedback remains unclear [ 13 ]. Here we reveal that polarization of the auxin efflux carrier PIN-FORMED 1 (PIN1) is regulated by the auxin response transcription factor MONOPTEROS (MP) [ 14 ]. We find that in the shoot, cell polarity patterns follow MP expression, which in turn follows auxin distribution patterns. By perturbing MP activity both globally and locally, we show that localized MP activity is necessary for the generation of polarity convergence patterns and that localized MP expression is sufficient to instruct PIN1 polarity directions non-cell autonomously, toward MP-expressing cells. By expressing MP in the epidermis of mp mutants, we further show that although MP activity in a single-cell layer is sufficient to promote polarity convergence patterns, MP in sub-epidermal tissues helps anchor these polarity patterns to the underlying cells. Overall, our findings reveal a patterning module in plants that determines organ position by orienting transport of the hormone auxin toward cells with high levels of MP-mediated auxin signaling. We propose that this feedback process acts broadly to generate periodic plant architectures. [ABSTRACT FROM AUTHOR]

The IQSec/BRAG proteins are a subfamily of Arf-nucleotide exchange factors. Since their discovery almost 15 y ago, the BRAGs have been reported to be involved in diverse physiological processes from myoblast fusion, neuronal pathfinding and angiogenesis, to pathophysiological processes including X-linked intellectual disability and tumor metastasis. In this review we will address how, in each of these situations, the BRAGs are thought to regulate the surface levels of adhesive and signaling receptors. While in most cases BRAGs are thought to enhance the endocytosis of these receptors, how they achieve this remains unclear. Similarly, while all 3 BRAG proteins contain calmodulin-binding IQ motifs, little is known about how their activities might be regulated by calcium. These are some of the questions that are likely to form the basis of future research. [ABSTRACT FROM AUTHOR]

Leaf vein pattern is proposed to be specified by directional auxin transport through presumptive vein cells. Activation of auxin response, which induces downstream genes that entrain auxin transport and lead to vascular differentiation, occurs through a set of transcription factors, the auxin response factors. In the absence of auxin, auxin response factors are inactive because they interact with repressor proteins, the Aux/IAA proteins. One member of the auxin response factor protein family, Auxin Response Factor 5/MONOPTEROS (MP), is critical to vein formation as indicated by reduced vein formation in loss-of-function MP alleles. We have identified a semi-dominant, gain-of-function allele of MP, autobahn or mp, which results in vein proliferation in leaves and cotyledons. mp is predicted to encode a truncated product that lacks domain IV required for interaction with its Aux/IAA repressor BODENLOS (BDL). We show that the truncated product fails to interact with BDL in yeast two-hybrid assays. Ectopic expression of MP targets including the auxin efflux protein PINFORMED1 (PIN1) further supports the irrepressible nature of mp. Asymmetric PIN1:GFP cellular localization does not occur within the enlarged PIN1:GFP expression domains, suggesting the asymmetry requires differential auxin response in neighbouring cells. Organ initiation from mp meristems is altered, consistent with disruption to source/sink relationships within the meristem and possible changes in gene expression. Finally, mp anthers fail to dehisce and their indehiscence can be relieved by jasmonic acid treatment, suggesting a specific role for MP in late anther development. [ABSTRACT FROM AUTHOR]

Silver birch (Betula pendula Roth) is an economically important species in Northern Europe. The current research focused on the molecular background of different xylogenesis scenarios in the birch trunks. The study objects were two forms of silver birch, silver birch trees, and Karelian birch trees; the latter form is characterized by the formation of two types of wood, non-figured (straight-grained) and figured, respectively, while it is currently not clear which factors cause this difference. We identified VND/NST/SND genes that regulate secondary cell wall biosynthesis in the birch genome and revealed differences in their expression in association with the formation of xylem with different ratios of structural elements. High expression levels of BpVND7 accompanied differentiation of the type of xylem which is characteristic of the species. At the same time, the appearance of figured wood was accompanied by the low expression levels of the VND genes and increased levels of expression of NST and SND genes. We identified BpARF5 as a crucial regulator of auxin-dependent vascular patterning and its direct target—BpHB8. A decrease in the BpARF5 level expression in differentiating xylem was a specific characteristic of both Karelian birch with figured and non-figured wood. Decreased BpARF5 level expression in non-figured trees accompanied by decreased BpHB8 and VND/NST/SND expression levels compared to figured Karelian birch trees. According to the results obtained, we suggested silver birch forms differing in wood anatomy as valuable objects in studying the regulation of xylogenesis. [ABSTRACT FROM AUTHOR]

Contact sites between the endoplasmic reticulum (ER) and plasma membrane (PM) regulate both non-vesicular lipid transfer as well as Ca2+ signaling with multiple interactions between the two pathways. Here I discuss recent findings that offer exciting insights into the role of store-operated Ca2+ entry (SOCE), Oxysterol-binding protein (OSBP)-related proteins ORP3, Arf5 and the Arf GEF IQSec1 in this crosstalk and how they regulate cell migration and focal adhesion disassembly. [ABSTRACT FROM AUTHOR]

Mammalian female meiosis must be tightly regulated to produce high-quality mature oocytes for subsequent regular fertilization and healthy live birth of the next generation. GTPases control many important signal pathways involved in diverse cellular activities. ADP-ribosylation factor family members (Arfs) in mice possess GTPase activities, and some members have been found to function in meiosis. However, whether other Arfs play a role in meiosis is unknown. In this study, we found that Arl2 and Arf5 are the richest among Arfs in mouse oocytes, and they are more abundant in oocytes than in granular cells. Furthermore, Arl2 and Arf5 depletion both impeded meiotic progression, but by affecting spindles and microfilaments, respectively. Moreover, Arl2 and Arf5 depletion both significantly increased regular reactive oxygen species levels and decreased mitochondrial membrane potential and autophagy, indicating that oocyte quality was damaged by Arl2 and Arf5 depletion. These results suggest that Arl2 and Arf5 are two novel essential GTPases required for oocyte meiosis and quality control., (© 2020 Wiley Periodicals LLC.)

Contact sites between the endoplasmic reticulum (ER) and plasma membrane (PM) regulate both non-vesicular lipid transfer as well as Ca 2+ signaling with multiple interactions between the two pathways. Here I discuss recent findings that offer exciting insights into the role of store-operated Ca 2+ entry (SOCE), Oxysterol-binding protein (OSBP)-related proteins ORP3, Arf5 and the Arf GEF IQSec1 in this crosstalk and how they regulate cell migration and focal adhesion disassembly., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Plant-growth-promoting rhizobacteria (PGPR) improve plant growth by altering the root architecture, although the mechanisms underlying this alteration have yet to be unravelled. Through microarray analysis of PGPR-treated rice roots, a large number of differentially regulated genes were identified. Ectopic expression of one of these genes, OsASR6 (ABA STRESS RIPENING6), had a remarkable effect on plant growth in Arabidopsis. Transgenic lines over-expressing OsASR6 had larger leaves, taller inflorescence bolts and greater numbers of siliques and seeds. The most prominent effect was observed in root growth, with the root biomass increasing four-fold compared with the shoot biomass increase of 1.7-fold. Transgenic OsASR6 over-expressing plants showed higher conductance, transpiration and photosynthesis rates, leading to an ˜30% higher seed yield compared with the control. Interestingly, OsASR6 expression led to alterations in the xylem structure, an increase in the xylem vessel size and altered lignification, which correlated with higher conductance. OsASR6 is activated by auxin and, in turn, increases auxin responses and root auxin sensitivity, as observed by the increased expression of auxin-responsive genes, such as SAUR32 and PINOID , and the key auxin transcription factor, ARF5. Collectively, these phenomena led to an increased root density. The effects of OsASR6 expression largely mimic the beneficial effects of PGPRs in rice, indicating that OsASR6 activation may be a key factor governing PGPR-mediated changes in rice. OsASR6 is a potential candidate for the manipulation of rice for improved productivity. [ABSTRACT FROM AUTHOR]

Patterning of numerous features of plants depends on transduction of the auxin signal. Auxin signaling is mediated by several pathways, the best understood of which relies on the function of the MONOPTEROS (MP) gene. Seven mp mutant alleles have been described in the widely used Columbia background of Arabidopsis: two extensively characterized and five only partially characterized. One of these five mp alleles appears to be extinct and thus unavailable for analysis. We show that two of the four remaining, partially characterized mp alleles reported to be in the Columbia background are in fact not in this background. We extend characterization of the remaining two Columbia alleles of mp, and we identify and characterize four new alleles of mp in the Columbia background, among which the first low-expression allele of mp and the strongest Columbia allele of mp. These genetic resources provide the research community with new experimental opportunities for insight into the function of MP-dependent auxin signaling in plant development., (Copyright © 2013 Wiley Periodicals, Inc.)