Title: WRKY15 Suppresses Tracheary Element Differentiation Upstream of VND7 During Xylem Formation

Shating Ge, Xiaofei Han, Xuwen Xu, Yiming Shao, Qiankun Zhu, Yidong Liu, Juan Du, Juan Xu, Shuqun Zhang

Published April 2020. DOI: https://doi.org/10.1105/tpc.19.00689

Abstract

Formation of vascular cylinder, a structure critical to water and nutrient transport in higher plants, is a highly regulated process. Here we identify WRKY15 as an important regulator that suppresses tracheary element (TE) differentiation. Overexpression of WRKY15 results in discontinuous protoxylem vessel files and TEs with reduced spiral wall thickening/lignification. Suppression of WRKY15 function by expressing WRKY15-EAR, a dominant-negative WRKY15 variant, leads to extra protoxylem vessels and ectopic TEs with increased spiral wall thickening/lignification. Ectopic TE formation in the root cortex and hypocotyl/leaf epidermis reveals that the suppression of WRKY15 function is sufficient to trigger the transdifferentiation of other types of cells to TEs. Expression profiling, RT-qPCR, and reporter analyses revealed that WRKY15 suppresses the expression of VND7, a master transcriptional regulator that promotes TE differentiation. We propose that WRKY15 negatively regulates VND7 expression indirectly based on the facts that 1) the absence of W-box in the promoter of VND7, and 2) WRKY15 and VND7 are expressed in different cells in the vascular cylinder with WRKY15 expressed in the procambial cells and VND7 in the protoxylem poles of procambium and differentiating TEs. Future research is needed to reveal the details underlying the interaction of WRKY15 and VND7 in plant vascular development.

Link: http://www.plantcell.org/content/early/2020/04/23/tpc.19.00689