WOX4 and WOX14 act downstream of the PXY receptor kinase to regulate plant vascular proliferation independently of any role in vascular organisation

Abstract

In plants, the cambium and procambium are meristems from which vascular tissue is derived. In contrast to most plant cells, stem cells within these tissues are thin and extremely long. They are particularly unusual as they divide down their long axis in a highly ordered manner, parallel to the tangential axis of the stem. CLAVATA3-LIKE/ESR-RELATED 41 (CLE41) and PHLOEM INTERCALATED WITH XYLEM (PXY) are a multifunctional ligand-receptor pair that regulate vascular cell division, vascular organisation and xylem differentiation in vascular tissue. A transcription factor gene, WUSCHEL HOMEOBOX RELATED 4 (WOX4) has been shown to act downstream of PXY. Here we show that WOX4 acts redundantly with WOX14 in the regulation of vascular cell division, but that these genes have no function in regulating vascular organisation. Furthermore, we identify an interaction between PXY and the receptor kinase ERECTA (ER) that affects the organisation of the vascular tissue but not the rate of cell division, suggesting that cell division and vascular organisation are genetically separable. Our observations also support a model whereby tissue organisation and cell division are integrated via PXY and ER signalling, which together coordinate development of different cell types that are essential for normal stem formation.

Plant GSK3 proteins regulate xylem cell differentiation downstream of TDIF–TDR signalling

“…In hypocotyls, TDIF did not reduce xylem cell numbers (Fig. 6e), which is consistent with results reported previously 16,31,32 . This might result from a counterbalance between TDIF-dependent reduced xylem cells and ectopic xylem formation as a secondary effect arising from TDIF-induced random procambial cell proliferation (Fig.…”

“…7i-k). On the other hand, wox4-1 showed narrower gap region existing between pAPL-GUS expression domain and xylem region than that in the WT, but rarely did the adjacency of xylem and phloem cells, coinciding with previous reports 18,32 ( Fig. 7l-n).…”

“…In the regulation of cell proliferation, WUS and its family members play central roles 50 . Especially, WOX4 has been implicated in the promotion of cell proliferation in vascular meristems downstream of TDIF signalling 18,32 . By genetic analysis, we showed that GSK3s and BES1 function independently of WOX4 in the maintenance of procambial cells.…”

“…The adjacency phenotype in tdr results from the exhaustion of procambial cells by a combination of the inhibition of procambial cell proliferation and the consumption of procambial cells via enhanced xylem differentiation 16,18 . wox4-1 mutant, which shows only a defect in TDIF-dependent promotion of procambial cell proliferation in contrast to gsk3 mutants 18,32 , exhibits the reduction of procambial cell layers but not the adjacency of xylem and phloem cells 18,32 . Then, we investigated a genetic relationship between TDR-GSK3s and TDR-WOX4 pathways by using bikinin and wox4-1 mutant, and also using markers such as pAPL-GUS for phloem cells 34 , pTDR-GUS for procambial cells 16 and secondary wall thickenings for xylem cells.…”

The VASCULATURE COMPLEXITY AND CONNECTIVITY Gene Encodes a Plant-Specific Protein Required for Embryo Provasculature Development

“…Three Leu-rich repeat RLKs, RECEPTOR-LIKE PROTEIN KINASE1, TOADSTOOL2, and BRASSINOSTEROID-INSENSITIVE1-LIKE2 (BRL2), are known to be involved in vascular patterning in embryos (Nodine et al, 2007;Ceserani et al, 2009). Other RLKs, such as PHLOEM INTERCALATED WITH XYLEM (Fisher and Turner, 2007;Etchells and Turner, 2010;Etchells et al, 2013), XYLEM INTERMIXED WITH PHLOEM1 (Bryan et al, 2012), MORE LATERAL GROWTH1, and REDUCED IN LATERAL GROWTH1 (Agusti et al, 2011), control vasculature identity and development in adult tissues, but their roles in embryonic vasculature patterning have not been analyzed.…”