HYPONASTIC LEAVES 1 is required for proper establishment of auxin gradient in apical hooks.
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ABSTRACT:
SUBMITTER: Vacs P
PROVIDER: S-EPMC8644733 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Hyponastic Leaves 1 (HYL1) [also known as Double-stranded RNA-Binding protein 1 (DRB1)] is a double-stranded RNA-binding protein involved in microRNA (miRNA) processing in plants. It is a core component of the Microprocessor complex and enhances the efficiency and precision of miRNA processing by the Dicer-Like 1 protein. In this work, we report a novel function of the HYL1 protein in the transcription of miRNA (MIR) genes. HYL1 colocalizes with RNA polymerase II and affects its distribution along MIR genes. Moreover, proteomic experiments revealed that the HYL1 protein interacts with many transcription factors. Finally, we show that the action of HYL1 is not limited to MIR genes and impacts the expression of many other genes, a majority of which are involved in plastid organization. These discoveries indicate HYL1 as an additional player in gene regulation at the transcriptional level, independent of its role in miRNA biogenesis.
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Project description:Auxins are crucial for plant growth and development. Auxin signalling primarily depends on four partially redundant F-box proteins of the TIR1/AFB2 Auxin Receptor (TAAR) clade to trigger the degradation of AUX/IAA transcriptional repressors. Auxin signalling is a balanced system which involves complex feedback regulations. miR393 regulation of TAAR genes is important for different developmental programs and for responses to environment. However, so far, the relevance of the two MIR393 genes for Arabidopsis leaf development and their significance for auxin signalling homeostasis have not been evaluated. First, our analyses of mir393a-1 and mir393b-1 mutants and of mir393ab double mutant show that the two genes have only partially redundant functions for leaf development. Expression analyses of typical auxin-induced reporter genes have shown that the loss of miR393 lead to several unanticipated changes in auxin signalling. The expression of DR5pro:GUS is decreased, the expression of primary AUX/IAA auxin-responsive genes is slightly increased and the degradation of the AXR3-NT:GUS reporter protein is delayed in mir393ab mutants. Additional analyses using synthetic auxin and auxin antagonists indicated that miR393 deficient mutants have higher levels of endogenous AUX/IAA proteins, which in turn create a competition for degradation. We propose that the counter-intuitive changes in the expression of AUX/IAA genes and in the accumulation of AUX/IAA proteins are explained by the intrinsic nature of AUX/IAA genes which are feedback regulated by the AUX/IAA proteins which they produce. Altogether our experiments provide an additional highlight of the complexity of auxin signaling homeostasis and show that miR393 is an important component of this homeostasis.
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Project description:Biogenesis of plant microRNAs (miRNAs) takes place in nuclear dicing bodies (D-bodies), where the ribonulease III-type enzyme Dicer-like 1 (DCL1) processes primary transcripts of miRNAs (pri-miRNAs) into miRNA/miRNA* (*, passenger strand) duplexes from either base-to-loop or loop-to-base directions. Hyponastic Leaves 1 (HYL1), a double-stranded RNA-binding protein, is crucial for efficient and accurate processing. However, whether HYL1 has additional function remains unknown. Here, we report that HYL1 plays a noncanonical role in protecting pri-miRNAs from nuclear exosome attack in addition to ensuring processing. Loss of functions in SOP1 or HEN2, two cofactors of the nucleoplasmic exosome, significantly suppressed the morphological phenotypes of hyl1-2 Remarkably, mature miRNAs generated from loop-to-base processing were partially but preferentially restored in the hyl1 sop1 and hyl1 hen2 double mutants. Accordingly, loop-to-base-processed pri-miRNAs accumulated to higher levels in double mutants. In addition, dysfunction of HEN2, but not of SOP1, in hyl1-2 resulted in overaccumulation of many base-to-loop-processed pri-miRNAs, with most of their respective miRNAs unaffected. In summary, our findings reveal an antagonistic action of exosome in pri-miRNA biogenesis and uncover dual roles of HYL1 in stabilizing and processing of pri-miRNAs.
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Project description:Auxin produced by an active primary shoot apex is transported down the main stem and inhibits the growth of the axillary buds below it, contributing to apical dominance. Here we use Arabidopsis thaliana cytokinin (CK) biosynthetic and signalling mutants to probe the role of CK in this process. It is well established that bud outgrowth is promoted by CK, and that CK synthesis is inhibited by auxin, leading to the hypothesis that release from apical dominance relies on an increased supply of CK to buds. Our data confirm that decapitation induces the expression of at least one ISOPENTENYLTRANSFERASE (IPT) CK biosynthetic gene in the stem. We further show that transcript abundance of a clade of the CK-responsive type-A Arabidopsis response regulator (ARR) genes increases in buds following CK supply, and that, contrary to their typical action as inhibitors of CK signalling, these genes are required for CK-mediated bud activation. However, analysis of the relevant arr and ipt multiple mutants demonstrates that defects in bud CK response do not affect auxin-mediated bud inhibition, and increased IPT transcript levels are not needed for bud release following decapitation. Instead, our data suggest that CK acts to overcome auxin-mediated bud inhibition, allowing buds to escape apical dominance under favourable conditions, such as high nitrate availability.
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Project description:MicroRNAs have turned out to be important regulators of gene expression. These molecules originate from longer transcripts that are processed by ribonuclease III (RNAse III) enzymes. Dicer proteins are essential RNAse III enzymes that are involved in the generation of microRNAs (miRNAs) and other small RNAs. The correct function of Dicer relies on the participation of accessory dsRNA binding proteins, the exact function of which is not well-understood so far. In plants, the double stranded RNA binding protein Hyponastic Leaves 1 (HYL1) helps Dicer Like protein (DCL1) to achieve an efficient and precise excision of the miRNAs from their primary precursors. Here we dissected the regions of HYL1 that are essential for its function in Arabidopsis thaliana plant model. We generated mutant forms of the protein that retain their structure but affect its RNA-binding properties. The mutant versions of HYL1 were studied both in vitro and in vivo, and we were able to identify essential aminoacids/residues for its activity. Remarkably, mutation and even ablation of one of the purportedly main RNA binding determinants does not give rise to any major disturbances in the function of the protein. We studied the function of the mutant forms in vivo, establishing a direct correlation between affinity for the pri-miRNA precursors and protein activity.
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Project description:Phototropism is a growth response allowing plants to align their photosynthetic organs toward incoming light and thereby to optimize photosynthetic activity. Formation of a lateral gradient of the phytohormone auxin is a key step to trigger asymmetric growth of the shoot leading to phototropic reorientation. To identify important regulators of auxin gradient formation, we developed an auxin flux model that enabled us to test in silico the impact of different morphological and biophysical parameters on gradient formation, including the contribution of the extracellular space (cell wall) or apoplast. Our model indicates that cell size, cell distributions, and apoplast thickness are all important factors affecting gradient formation. Among all tested variables, regulation of apoplastic pH was the most important to enable the formation of a lateral auxin gradient. To test this prediction, we interfered with the activity of plasma membrane H? -ATPases that are required to control apoplastic pH. Our results show that H? -ATPases are indeed important for the establishment of a lateral auxin gradient and phototropism. Moreover, we show that during phototropism, H? -ATPase activity is regulated by the phototropin photoreceptors, providing a mechanism by which light influences apoplastic pH.
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Project description:Hedgehog (Hh) signalling is important in development, stem cell biology and disease. In a variety of tissues, Hh acts as a morphogen to regulate growth and cell fate specification. Several hypotheses have been proposed to explain morphogen movement, one of which is transport along filopodia-like protrusions called cytonemes. Here, we analyse the mechanism underlying Hh movement in the wing disc and the abdominal epidermis of Drosophila melanogaster. We show that, in both epithelia, cells generate cytonemes in regions of Hh signalling. These protrusions are actin-based and span several cell diameters. Various Hh signalling components localize to cytonemes, as well as to punctate structures that move along cytonemes and are probably exovesicles. Using in vivo imaging, we show that cytonemes are dynamic structures and that Hh gradient establishment correlates with cytoneme formation in space and time. Indeed, mutant conditions that affect cytoneme formation reduce both cytoneme length and Hh gradient length. Our results suggest that cytoneme-mediated Hh transport is the mechanistic basis for Hh gradient formation.
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Project description:The Patched-related superfamily of transmembrane proteins can transport lipids or other hydrophobic molecules across cell membranes. While the Hedgehog receptor Patched has been intensively studied, much less is known about the biological roles of other Patched-related family members. Caenorhabditis elegans has a large number of Patched-related proteins, despite lacking a canonical Hedgehog pathway. Here, we show that PTR-4 promotes the assembly of the precuticle apical extracellular matrix, a transient and molecularly distinct matrix that precedes and patterns the later collagenous cuticle or exoskeleton. ptr-4 mutants share many phenotypes with precuticle mutants, including defects in eggshell dissolution, tube shaping, alae (cuticle ridge) structure, molting, and cuticle barrier function. PTR-4 localizes to the apical side of a subset of outward-facing epithelia, in a cyclical manner that peaks when precuticle matrix is present. Finally, PTR-4 is required to limit the accumulation of the lipocalin LPR-3 and to properly localize the Zona Pellucida domain protein LET-653 within the precuticle. We propose that PTR-4 transports lipids or other hydrophobic components that help to organize the precuticle and that the cuticle and molting defects seen in ptr-4 mutants result at least in part from earlier disorganization of the precuticle.
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Project description:Plants, although sessile, can reorient growth axes in response to changing environmental conditions. Phototropism and gravitropism represent adaptive growth responses induced by changes in light direction and growth axis orientation relative to gravitational direction, respectively. The nearly 80-year-old Cholodny-Went theory [Went, F. W. & Thimann, K. V. (1937) Phytohormones (Macmillan, New York)] predicts that formation of a gradient of the plant morphogen auxin is central to the establishment of tropic curvature. Loss of tropic responses in seedling stems of Arabidopsis thaliana mutants lacking the auxin-regulated transcriptional activator NPH4/ARF7 has further suggested that a gradient of gene expression represents an essential output from the auxin gradient. Yet the molecular identities of such output components, which are likely to encode proteins directly involved in growth control, have remained elusive. Here we report the discovery of a suite of tropic stimulus-induced genes in Brassica oleracea that are responsive to an auxin gradient and exhibit morphologically graded expression concomitant with, or before, observable curvature responses. These results provide compelling molecular support for the Cholodny-Went theory and suggest that morphologically graded transcription represents an important mechanism for interpreting tropically stimulated gradients of auxin. Intriguingly, two of the tropic stimulus-induced genes, EXPA1 and EXPA8, encode enzymes involved in cell wall extension, a response prerequisite for differential growth leading to curvatures, and are up-regulated before curvature in the flank that will elongate. This observation suggests that morphologically graded transcription likely leads to the graded expression of proteins whose activities can directly regulate the establishment and modulation of tropic curvatures.
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