Wounding triggers organ regeneration in many plant species, and application of plant hormones, such as auxin and cytokinin, enhances their regenerative capacities in tissue culture. Recent studies have identified several key players mediating wound- and/or plant hormone-induced cellular reprogramming, but the global architecture of gene regulatory relationships underlying plant cellular reprogramming is still far from clear. In this study, we uncovered a gene regulatory network (GRN) associated with plant cellular reprogramming by using an enhanced yeast one-hybrid (eY1H) screen systematically to identify regulatory relationships between 252 transcription factors (TFs) and 48 promoters. Our network analyses suggest that wound- and/or hormone-invoked signals exhibit extensive cross-talk and regulate many common reprogramming-associated genes via multilayered regulatory cascades. Our data suggest that PLETHORA 3 (PLT3), ENHANCER OF SHOOT REGENERATION 1 (ESR1) and HEAT SHOCK FACTOR B 1 (HSFB1) act as critical nodes that have many overlapping targets and potentially connect upstream stimuli to downstream developmental decisions. Interestingly, a set of wound-inducible APETALA 2/ETHYLENE RESPONSE FACTORs (AP2/ERFs) appear to regulate these key genes, which, in turn, form feed-forward cascades that control downstream targets associated with callus formation and organ regeneration. In addition, we found another regulatory pathway, mediated by LATERAL ORGAN BOUNDARY/ASYMMETRIC LEAVES 2 (LOB/AS2) TFs, which probably plays a distinct but partially overlapping role alongside the AP2/ERFs in the putative gene regulatory cascades. Taken together, our findings provide the first global picture of the GRN governing plant cell reprogramming, which will serve as a valuable resource for future studies.
ABSTRACT Stem cells play important roles in animal and plant biology as they sustain morphogenesis and tissue replenishment following aging or injuries. In plants, stem cells are embedded in multicellular structures called meristems and the formation of new meristems is essential for the plastic expansion of the highly branched shoot and root systems. In particular, axillary meristems that produce lateral shoots arise from the division of boundary domain cells at the leaf base. The CUP-SHAPED COTYLEDON ( CUC ) genes are major determinants of the boundary domain and are required for axillary meristem initiation. However, how axillary meristems get structured and how stem cells become established de novo remains elusive. Here, we show that two NGATHA-LIKE transcription factors, DPA4 and SOD7, redundantly repress CUC expression in the initiating axillary meristem. Ectopic boundary fate leads to abnormal growth and organisation of the axillary meristem and prevents de novo stem cell establishment. Floral meristems of the dpa4 sod7 double mutant show a similar delay in stem cell de novo establishment. Altogether, while boundary fate is required for the initiation of axillary meristems, our work reveals how it is later repressed to allow proper meristem establishment and de novo stem cell niche formation.
Abstract Plants shed organs such as leaves, petals, or fruits through the process of abscission. Monitoring cues such as age, resource availability, and biotic and abiotic stresses allow plants to abscise organs in a timely manner. How these signals are integrated into the molecular pathways that drive abscission is largely unknown. The INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) gene is one of the main drivers of floral organ abscission in Arabidopsis and is known to transcriptionally respond to most abscission-regulating cues. By interrogating the IDA promoter in silico and in vitro, we identified transcription factors that could potentially modulate IDA expression. We probed the importance of ERF- and WRKY-binding sites for IDA expression during floral organ abscission, with WRKYs being of special relevance to mediate IDA up-regulation in response to biotic stress in tissues destined for separation. We further characterized WRKY57 as a positive regulator of IDA and IDA-like gene expression in abscission zones. Our findings highlight the promise of promoter element-targeted approaches to modulate the responsiveness of the IDA signaling pathway to harness controlled abscission timing for improved crop productivity.
Abstract Plants shed organs like leaves, petals or fruits through the process of abscission. Monitoring cues like age, resource availability, biotic and abiotic stresses allows plants to abscise organs in a timely manner. How these signals are integrated in the molecular pathways that drive abscission is largely unknown. The INFLORESCENCE DEFICIENT IN ABSCISSION ( IDA ) gene is one of the main drivers of floral organ abscission in Arabidopsis and is known to transcriptionally respond to most abscission-regulating cues. Interrogating the IDA promoter in silico and in vitro we identified transcription factors that can potentially modulate IDA expression. We functionally characterized the importance of ERF and WRKY binding sites for IDA expression during floral organ abscission, with WRKYs being of special relevance to mediate IDA upregulation in response to biotic stress in tissues destined for separation. We further characterized WRKY57 as a positive regulator of IDA and IDA - like gene expression in abscission zones. Our findings highlight the promise of promoter element-targeted approaches to modulate the responsiveness of the IDA signaling pathway to harness controlled abscission timing for improved crop productivity. Highlight ERF and WRKY transcription factors distinctly contribute to the regulation of IDA expression and thereby abscission timing. WRKY57 modulates abscission via redundant IDA/IDA-like peptides.
The cambium and procambium generate the majority of biomass in vascular plants. These meristems constitute a bifacial stem cell population from which xylem and phloem are specified on opposing sides by positional signals. The PHLOEM INTERCALATED WITH XYLEM (PXY) receptor kinase promotes vascular cell division and organization. However, how these functions are specified and integrated is unknown. Here, we mapped a putative PXY-mediated transcriptional regulatory network comprising 690 transcription factor-promoter interactions in Arabidopsis (
In multicellular organisms the specification of distinct tissues within organs allows compartmentation of complex processes. However, the mechanisms that allow gene expression to be restricted to such tissues are poorly understood. To better understand this process, we focused on bundle sheath expression of the gene encoding the MYB76 transcription factor in Arabidopsis thaliana. Functional and computational analyses were combined to identify a seven-nucleotide motif within a DNaseI hypersensitive site in the MYB76 promoter that is necessary and sufficient to direct gene expression to bundle sheath cells. Thus, combining information from DNaseI hypersensitivity assays with classical truncation analysis allowed the rapid identification of a single cis-element that governs cell type-specificity. This motif is conserved in the Brassicaceae, acts to positively regulate gene expression, and is recognised in planta by two DREB transcription factors. In contrast to previous studies, these data indicate that the patterning of gene expression to specific cell types can be mediated by relatively simple interactions between cis-elements and transcription factors. Moreover, as the element in the MYB76 promoter is short and can be oligomerized to tune expression levels it is well-suited for use in synthetic biology applications that require tissue specific expression in plants.
Abstract Stem cells play important roles in animal and plant biology, as they sustain morphogenesis and tissue replenishment following aging or injury. In plants, stem cells are embedded in multicellular structures called meristems. The formation of new meristems is essential for the plastic expansion of the highly branched shoot and root systems. In particular, axillary meristems (AMs) that produce lateral shoots arise from the division of boundary domain cells at the leaf base. The CUP-SHAPED COTYLEDON (CUC) genes are major determinants of the boundary domain and are required for AM initiation. However, how AMs get structured and how stem cells become established de novo remain elusive. Here, we show that two NGATHA-LIKE (NGAL) transcription factors, DEVELOPMENT-RELATED PcG TARGET IN THE APEX4 (DPA4)/NGAL3 and SUPPRESSOR OF DA1-1 7 (SOD7)/NGAL2, redundantly repress CUC expression in initiating AMs of Arabidopsis thaliana. Ectopic boundary fate leads to abnormal growth and organization of the AM and prevents de novo stem cell establishment. Floral meristems of the dpa4 sod7 double mutant show a similar delay in de novo stem cell establishment. Altogether, while boundary fate is required for the initiation of AMs, our work reveals how it is later repressed to allow proper meristem establishment and de novo stem cell niche formation.
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