A PXY-Mediated Transcriptional Network Integrates Signaling Mechanisms to Control Vascular Development in Arabidopsis
Smit, Margot ; Mcgregor, Shauni ; Sun, Heng ; Gough, Catherine ; Bågman, Anne-Maarit ; Soyars, Cara L. ; Kroon, Johan T.M. ; Gaudinier, Allison ; Williams, Clara J. ; Yang, Xiyan ; Nimchuk, Zachary L. ; Weijers, Dolf ; Turner, Simon R. ; Brady, Siobhan M. ; Etchells, Peter - \ 2020
The Plant Cell 32 (2020)2. - ISSN 1040-4651
Vascular meristems generate the majority of biomass in higher plants. They 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 organisation. However, how these functions are specified and integrated is unknown. Here, a putative PXY-mediated transcriptional regulatory network comprised of 690 transcription factor-promoter interactions was mapped. Among these interactions was a feed-forward loop containing transcription factors WUSCHEL HOMEOBOX RELATED 14 (WOX14) and TARGET OF MONOPTEROS 6 (TMO6), which each regulate the expression of a third transcription factor, LATERAL ORGAN BOUNDARIES DOMAIN 4 (LBD4). PXY signalling in turn regulates the WOX14, TMO6, LBD4 loop to control vascular proliferation. Genetic interaction between LBD4 and PXY suggests that LBD4 marks the phloem-procambium boundary, thus defining the shape of the vascular bundle. These data collectively support a novel mechanism that influences recruitment of cells into the phloem lineage, and defines the role of PXY signalling in this context to the arrangement of vascular tissue.
Theoretical approaches to understanding root vascular patterning : A consensus between recent models
Mellor, Nathan ; Adibi, Milad ; El-Showk, Sedeer ; Rybel, Bert De; King, John ; Mähönen, Ari Pekka ; Weijers, Dolf ; Bishopp, Anthony ; Etchells, Peter - \ 2017
Journal of Experimental Botany 68 (2017)1. - ISSN 0022-0957 - p. 5 - 16.
Auxin - Cytokinin - Mathematical modeling - Organ patterning - Systems biology - Vascular development
The root vascular tissues provide an excellent system for studying organ patterning, as the specification of these tissues signals a transition from radial symmetry to bisymmetric patterns. The patterning process is controlled by the combined action of hormonal signaling/transport pathways, transcription factors, and miRNA that operate through a series of non-linear pathways to drive pattern formation collectively. With the discovery of multiple components and feedback loops controlling patterning, it has become increasingly difficult to understand how these interactions act in unison to determine pattern formation in multicellular tissues. Three independent mathematical models of root vascular patterning have been formulated in the last few years, providing an excellent example of how theoretical approaches can complement experimental studies to provide new insights into complex systems. In many aspects these models support each other; however, each study also provides its own novel findings and unique viewpoints. Here we reconcile these models by identifying the commonalities and exploring the differences between them by testing how transferable findings are between models. New simulations herein support the hypothesis that an asymmetry in auxin input can direct the formation of vascular pattern. We show that the xylem axis can act as a sole source of cytokinin and specify the correct pattern, but also that broader patterns of cytokinin production are also able to pattern the root. By comparing the three modeling approaches, we gain further insight into vascular patterning and identify several key areas for experimental investigation.
A brief history of the TDIF-PXY signalling module : Balancing meristem identity and differentiation during vascular development
Etchells, J.P. ; Smit, M.E. ; Gaudinier, Allison ; Williams, Clara J. ; Brady, Siobhan M. - \ 2016
New Phytologist 209 (2016)2. - ISSN 0028-646X - p. 474 - 484.
Cambium - Phloem - Procambium - Signalling - Vascular development - Xylem
A significant proportion of terrestrial biomass is constituted of xylem cells that make up woody plant tissue. Xylem is required for water transport, and is present in the vascular tissue with a second conductive tissue, phloem, required primarily for nutrient transport. Both xylem and phloem are derived from cell divisions in vascular meristems known as the cambium and procambium. One major component that influences several aspects of plant vascular development, including cell division in the vascular meristem, vascular organization and differentiation of vascular cell types, is a signalling module characterized by a peptide ligand called TRACHEARY ELEMENT DIFFERENTIATION INHIBITORY FACTOR (TDIF) and its cognate receptor, PHLOEM INTERCALATED WITH XYLEM (PXY). In this review, we explore the literature that describes signalling components, phytohormones and transcription factors that interact with these two central factors, to control the varying outputs required in vascular tissues for normal organization and elaboration of plant vascular tissue.