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Light regulates xylem cell differentiation via PIF in Arabidopsis

ABSTRACT: Water transport is required for photosynthesis; thus plant vascular development must proceed such that water demands can be met during formation of new organs. Precise regulation of the balance between cell proliferation and differentiation in the cambial meristem defines formation of xylem and phloem, which constitute the vascular tissues. The TDIF-PXY/TDR signalling pathway is central to this process1. Peptide ligand, TDIF, encoded by CLE41 and CLE44 2, activates PXY/TDR receptors to maintain proliferative cambium. Cambium cells differentiate to xylem or phloem in the absence of active TDIF-PXY/TDR complexes. Vascular development is stimulated by light. After gemination, light induces the establishment of photoautotrophic growth via photosynthesis. Consequently, the differentiation of vascular cells must occur to favour the transport of water and minerals from the soil to the green tissues and newly developing organs. Plants perceive light through the action of photoreceptors, which modulate the activity of the transcription factors that orchestrate development. Despite the association between light signalling and vascular development, molecular mechanisms linking the two are unknown. Our work shows that vascular differentiation is inhibited in the dark by a mechanism that depends on PIF transcription factors. The dark accumulation of PIFs is necessary for CLE44 induction and thus maintenance of undifferentiated vasculature. In illuminated environments, PIF inactivation by photoreceptors causes a decrease in CLE44 expression. CLE44 reduction, in turn, leads to reduced PXY/TDR signalling which induces the xylem differentiation required to fulfil the water demands associated with photoautotrophic development.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE178268 | GEO | 2022/07/18

REPOSITORIES: GEO

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Project description:Vascular cambium is a secondary meristem which produces xylem (wood) inwards and phloem (bark) outwards. The activity of cambium leads to expansion in the diameters in plants, that is, secondary growth, and thus contributes to biomass increase. The regulation of cambium development is at multilevel including phytohormones and peptide-receptor kinase (CLE41/44-PXY) signalling pathways. However, only limited progress has been made on the transcriptional regulation level. To construct the transcriptional network that regulates cambium development, we performed a genome wide transcript profiling in sorted procambial and cambial cells in Arabidopsis roots. More than 500 genes were identified as cambium abundant genes via comparison against transcriptomes of other Arabidopsis root cell types. We then investigated the roles of almost all the cambial transcription factors (TFs) and some of their homologous genes during secondary growth. Many of the candidate TFs were highly expressed in cambium based on the promoter GUS fusion and in situ hybridization. An unbiased transcriptional regulatory network was constructed using transcript profiling data collected from inducible overexpression lines for selected candidate TFs and a few major nodes were identified in the network including WOX4 and KNAT1. Moreover, the severity of mutant phenotypes was predicted based on the network. Next, we used the predication as a guide and generated over 70 double mutants within the same or among different TF families to explore the genetic interactions of candidate genes. Phenotype characterization on the secondary growth of the mutants and the overexpression lines identified promoters and inhibitors of cambium activity. The phenotypic data also suggested the redundancy within and among TF families because the phenotypes could be enhanced when additional TFs were mutated. We also found that combinations of certain overexpression lines and mutants led to pronounced increase of cell proliferation or xylem differentiation and in the extreme case the formation of ectopic cambium. We herein propose that cambium development is orchestrated by a wide network at the transcriptional level, where each TF has a different contribution to cell proliferation and differentiation.

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Light regulates xylem cell differentiation via PIF in Arabidopsis

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