VASCULAR‐RELATED NAC‐DOMAIN 7 directly regulates the expression of a broad range of genes for xylem vessel formation

Abstract

SUMMARYThe Arabidopsis thaliana NAC domain transcription factor, VASCULAR-RELATED NAC-DOMAIN7 (VND7), acts as a key regulator of xylem vessel differentiation. In order to identify direct target genes of VND7, we performed global transcriptome analysis using Arabidopsis transgenic lines in which VND7 activity could be induced post-translationally. This analysis identified 63 putative direct target genes of VND7, which encode a broad range of proteins, such as transcription factors, IRREGULAR XYLEM proteins and proteolytic enzymes, known to be closely associated with xylem vessel formation. Recombinant VND7 protein binds to several promoter sequences present in candidate direct target genes: specifically, in the promoter of XYLEM CYSTEINE PEPTIDASE1, two distinct regions were demonstrated to be responsible for VND7 binding. We also found that expression of VND7 restores secondary cell wall formation in the fiber cells of inflorescence stems of nst1 nst3 double mutants, as well as expression of NAC SECONDARY WALL THICKENING PROMOTING FACTOR3 (NST3, however, the vessel-type secondary wall deposition was observed only as a result of VND7 expression. These findings indicated that VND7 upregulates, directly and/or indirectly, many genes involved in a wide range of processes in xylem vessel differentiation, and that its target genes are partially different from those of NSTs.

ATAF2, a NAC Transcription Factor, Binds to the Promoter and Regulates NIT2 Gene Expression Involved in Auxin Biosynthesis

“…It was reported that the NAC proteins recognize a sequence containing CATGT and harboring CACG as the core DNA binding site (Tran et al, 2004). Furthermore, vascular-related NACdomain 7 (VND7) and secondary wall-associated NAC domain protein 1 (SND1) directly bind to secondary wall NAC binding element (SNBE) in the target promoters (Yamaguchi et al, 2011;Zhong et al, 2010). However, still little is known about the NAC protein binding site in biological target gene of NAC.…”

A genome for gnetophytes and early evolution of seed plants

“…However, there has been longstanding debate whether gnetophyte 'vessels' are homologous to the 'vessels' of angiosperms. In angiosperms, VASCULAR-RELATED NAC-DOMAIN (VND) proteins VND1-7 are members of the NAC domain class of transcription factors, VND7 being a master regulator of vessel formation in A. thaliana 38 , and VND1-6 being upstream regulators of VND7 39 . Although five NAC domain genes were identified in the genome of G. montanum, no orthologues of VND7 or VND1-3 in the sister clade were identified, consistent with previous analyses of other gymnosperms 12 , and suggesting that these proteins are restricted to angiosperms ( Supplementary Fig.…”

Patterning of plant cell wall deposition by cortical microtubules

“…This similarity might indicate that microtubule disassembly in microtubule gaps and pits might share a common mechanism. This hypothesis is supported by the presence of AtKinesin-13A in protoxylem tissue 82 and MIDD1 being upregulated after VND7 induction 81 . Contrary to the reduced rescue rate observed in microtubule pits 55 , we find an increase in the rescue rate in microtubule gaps.…”

“…It is currently unclear what the molecular contributors are to protoxylem patterning. Nonetheless, ROP1 and ROP7 are putative candidates since these GTPases are upregulated after VND7 induction 81 .…”

“…These master regulators were coupled with an inducible expression system enabling ectopic induction of xylem transdifferentiation in tobacco BY-2 cells, Arabidopsis plants and poplar trees 51,55 . This proved to be a powerful tool to advance the study of xylem formation both via microarray analysis 51,81,130 and experimental cell biology [54][55][56]131,132 . In this thesis, inducible ectopic expression of VND7 is used as an experimental system to study functional properties of the microtubule array which templates the patterned deposition of cell wall material in developing protoxylem vessel elements.…”