Project description:The capacity for sustained cell division is a critical determinant of plant meristem development, and ultimately, organ size. This capacity is diminished in mutants lacking the microtubule-associated protein CLASP, and when brassinosteroid signaling is increased. Here, we discovered that CLASP is both targeted by and promotes activity of the brassinosteroid pathway in Arabidopsis root apical meristems. We show that enhanced brassinosteroid signalling reduces CLASP transcript and protein levels, and dramatically shifts microtubule organization to promote exit from the cell division cycle. Notably, CLASP sustains brassinosteroid signalling by fostering retrieval of endocytosed BRI1 receptors to the plasma membrane through the tethering of SNX1 vesicles to microtubules. clasp-1 null mutants have fewer BRI1 receptors, and impaired BR-mediated transcriptional activity and responses. Global transcript profiling confirmed the collapse of cell cycle activity in clasp-1 and revealed hormone crosstalk. Together, these findings reveal an unprecedented form of negative feedback that supports meristem homeostasis.
Project description:Auxin is a major plant hormone for both development and environmental adaptation. Auxin responses are context dependent and highly modulated by light, temperature, the circadian clock, brassinosteroid, and gibberellin, but the underlying mechanisms remain unclear. Here, we show that auxin signaling integrates with other signals through direct interactions of AUXIN RESPONSE FACTOR6 (ARF6) with PHYTOCHROME INTERACTING FACTOR4 (PIF4), the brassinosteroid-signaling transcription factor BZR1, and the gibberellin-signaling repressor RGA. ChIP-Seq and RNA-Seq experiments show that ARF6, PIF4, and BZR1 bind to largely overlapping targets in the genome and synergistically activate gene expression. In vitro and in vivo assays show that ARF6-promoter binding is enhanced by PIF4 and BZR1 but blocked by RGA. Furthermore, a tripartite HLH/bHLH module feedback regulates PIF activity and thus modulates auxin sensitivity according to additional developmental and environmental cues. Our results demonstrate a central growth-regulation transcriptional network that coordinates hormonal, environmental, and developmental control of cell elongation and plant growth. Genome-wide identification of ARF6 DNA-binding sites in etiolated Arabidopsis seedlings.
Project description:The effects of brassinosteroid signaling on shoot and root development have been characterized in great detail but did not identify a simple consistent positive or negative impact on a basic cellular parameter. Here we combined digital 3D single-cell shape analysis and single-cell mRNA sequencing to characterize root meristems and mature root segments of brassinosteroid-blind mutants and wildtype. These data demonstrate that brassinosteroid signaling neither affects cell volume nor cell proliferation capacity. Instead, brassinosteroid signaling is essential for the precise orientation of cell division planes and the extent and timing of anisotropic cell expansion. Moreover, we found that the cell-aligning effects of brassinosteroid signaling can propagate to normalize the anatomy of both adjacent and distant brassinosteroid-blind cells through non-cell-autonomous functions, which are sufficient to restore growth vigor. Finally, single-cell transcriptome data discern directly brassinosteroid-responsive genes from genes that can react non-cell-autonomously and highlight arabinogalactans as sentinels of brassinosteroid-dependent anisotropic cell expansion.
Project description:Auxin is a major plant hormone for both development and environmental adaptation. Auxin responses are context dependent and highly modulated by light, temperature, the circadian clock, brassinosteroid, and gibberellin, but the underlying mechanisms remain unclear. Here, we show that auxin signaling integrates with other signals through direct interactions of AUXIN RESPONSE FACTOR6 (ARF6) with PHYTOCHROME INTERACTING FACTOR4 (PIF4), the brassinosteroid-signaling transcription factor BZR1, and the gibberellin-signaling repressor RGA. ChIP-Seq and RNA-Seq experiments show that ARF6, PIF4, and BZR1 bind to largely overlapping targets in the genome and synergistically activate gene expression. In vitro and in vivo assays show that ARF6-promoter binding is enhanced by PIF4 and BZR1 but blocked by RGA. Furthermore, a tripartite HLH/bHLH module feedback regulates PIF activity and thus modulates auxin sensitivity according to additional developmental and environmental cues. Our results demonstrate a central growth-regulation transcriptional network that coordinates hormonal, environmental, and developmental control of cell elongation and plant growth. Seedlings (Col-0 and iaa3) were grown on medium containing 2 µM propiconazole (PPZ) in the dark for 5 days and treated with mock or 100 nM BL for 4 hr before harvesting for total RNA extraction.
Project description:Auxin is a major plant hormone for both development and environmental adaptation. Auxin responses are context dependent and highly modulated by light, temperature, the circadian clock, brassinosteroid, and gibberellin, but the underlying mechanisms remain unclear. Here, we show that auxin signaling integrates with other signals through direct interactions of AUXIN RESPONSE FACTOR6 (ARF6) with PHYTOCHROME INTERACTING FACTOR4 (PIF4), the brassinosteroid-signaling transcription factor BZR1, and the gibberellin-signaling repressor RGA. ChIP-Seq and RNA-Seq experiments show that ARF6, PIF4, and BZR1 bind to largely overlapping targets in the genome and synergistically activate gene expression. In vitro and in vivo assays show that ARF6-promoter binding is enhanced by PIF4 and BZR1 but blocked by RGA. Furthermore, a tripartite HLH/bHLH module feedback regulates PIF activity and thus modulates auxin sensitivity according to additional developmental and environmental cues. Our results demonstrate a central growth-regulation transcriptional network that coordinates hormonal, environmental, and developmental control of cell elongation and plant growth.
Project description:Auxin is a major plant hormone for both development and environmental adaptation. Auxin responses are context dependent and highly modulated by light, temperature, the circadian clock, brassinosteroid, and gibberellin, but the underlying mechanisms remain unclear. Here, we show that auxin signaling integrates with other signals through direct interactions of AUXIN RESPONSE FACTOR6 (ARF6) with PHYTOCHROME INTERACTING FACTOR4 (PIF4), the brassinosteroid-signaling transcription factor BZR1, and the gibberellin-signaling repressor RGA. ChIP-Seq and RNA-Seq experiments show that ARF6, PIF4, and BZR1 bind to largely overlapping targets in the genome and synergistically activate gene expression. In vitro and in vivo assays show that ARF6-promoter binding is enhanced by PIF4 and BZR1 but blocked by RGA. Furthermore, a tripartite HLH/bHLH module feedback regulates PIF activity and thus modulates auxin sensitivity according to additional developmental and environmental cues. Our results demonstrate a central growth-regulation transcriptional network that coordinates hormonal, environmental, and developmental control of cell elongation and plant growth.
Project description:The quiescent center (QC) plays an essential role during root development by creating a microenvironment that preserves the stem cell fate of its surrounding cells. Strikingly, in order to retain root structure, QC cells only occasionally self-renew, displaying a proliferation rate far below that of all other cells within the root meristem. Previously, the APC/CCCS52A2 ubiquitine ligase and brassinosteroid signaling pathways have been found to antagonistically control Arabidopsis thaliana QC cell proliferation. Here, we demonstrate that both pathways converge on the ERF115 transcription factor that acts as a rate-limiting factor of QC cell division through transcriptional control of the autocrine phytosulfokine PSK5 peptide hormone. ERF115 marks QC cell division but is restrained through proteolysis by the APC/CCCS52A2 ubiquitine ligase, whereas QC proliferation is driven by brassinosteroid-dependent ERF115 expression. Combined, these two antagonistic mechanisms delimit the ERF115-PSK5 activity and QC renewal. Our results reveal a unique cell cycle regulatory mechanism that accounts for the low proliferation rate of QC cells within a surrounding population of highly mitotic active cells. ChIP-seq analysis of genes bound by the ERF115 transcription factor, using mock ChIP with wild type cells as negative control. Analyzed by Illumina HiSeq
Project description:Plants acquire essential elements from inherently heterogeneous soils, in which phosphate and iron availabilities vary. Consequently, plants developed adaptive strategies to cope with low iron and low phosphate levels, including alternation between root growth enhancement and attenuation. How this adaptive response is achieved remains unclear. Here, we found that low iron accelerates the root growth of Arabidopsis thaliana by activating brassinosteroid signaling, whereas low-phosphate-induced high iron accumulation inhibited it. Altered hormone signaling intensity also modulated iron accumulation in the root elongation and differentiation zones, constituting a feedback response between brassinosteroid and iron. Surprisingly, the early effect of low iron levels on root growth required the brassinosteroid receptor but the hormone ligand was negligible. The brassinosteroid receptor inhibitor BKI1, the transcription factors BES1/BZR1 and the ferroxidase LPR1, stood at the base of this feedback loop. Hence, shared brassinosteroid and iron regulatory components link nutrient status to root morphology, thereby driving the adaptive response.
Project description:Plant height and grain size are important agronomic traits affecting rice yield. Various plant hormones participate in the regulation of plant height and grain size in rice. However, how these hormones cooperate to regulate plant height and grain size is poorly understood. In this study, we identified a brassinosteroid-related gene, hfr131, from an introgression line constructed using Oryza longistaminata, that caused brassinosteroid insensitivity and reduced plant height and grain length in rice. Further study showed that hfr131 is a new allele of OsBRI1 with a single-nucleotide polymorphism (G to A) in the coding region, leading to a T988I conversion at a conserved site of the kinase domain. An auxin response factor, OsARF17, could bind to the promoter region of HFR131 and positively regulated HFR131 expression, thereby regulating the plant height and grain length, and influencing brassinosteroid sensitivity. Haplotype analysis showed that the consociation of OsAFR17Hap1/HFR131Hap6 conferred an increase in grain length. Overall, this study identified hfr131 as a new allele of OsBRI1 that regulates plant height and grain length in rice, revealed that brassinosteroid and auxin might coordinate through OsARF17–HFR131 interaction, and provided a potential breeding target for improvement of rice yield.