Transcription Factors VND1-VND3 Contribute to Cotyledon Xylem Vessel Formation

Abstract

Arabidopsis () () to encode a group of NAC domain transcription factors that function as master regulators of xylem vessel element differentiation. These transcription factors activate the transcription of genes required for secondary cell wall formation and programmed cell death, key events in xylem vessel element differentiation. Because constitutive overexpression of VND6 and VND7 induces ectopic xylem vessel element differentiation, functional studies of VND proteins have largely focused on these two proteins. Here, we report the roles of VND1, VND2, and VND3 in xylem vessel formation in cotyledons. Using our newly established in vitro system in which excised Arabidopsis cotyledons are stimulated to undergo xylem cell differentiation by cytokinin, auxin, and brassinosteroid treatment, we found that ectopic xylem vessel element differentiation required VND1, VND2, and VND3 but not VND6 or VND7. The importance of VND1, VND2, and VND3 also was indicated in vivo; in the seedlings, xylem vessel element differentiation of secondary veins in cotyledons was inhibited under dark conditions. Furthermore, the light responsiveness of gene expression was disturbed in the mutant, and failed to recover lateral root development in response to the change of light conditions. These findings suggest that VND1 to VND3 have specific molecular functions, possibly linking light conditions to xylem vessel formation, during seedling development.

Interspecific Signaling Between the Parasitic Plant and the Host Plants Regulate Xylem Vessel Cell Differentiation in Haustoria of Cuscuta campestris

“…Next, in vitro-induced haustoria were cultivated on solid agarose media containing phytohormones that were previously shown to induce differentiation into xylem vessel cells Kubo et al, 2005;Kondo et al, 2016;Tan et al, 2018); however, this exposure did not stimulate the haustorial cell differentiation into xylem vessel cells in C. campestris. These results suggest that the host-derived signaling factors that trigger differentiation of search hyphae into the xylem cells are not phytohormones.…”

“…Next, to investigate the involvement of host-derived phytohormones in haustorium development, excised shoots with induced true haustoria were placed on solid agarose media containing four different phytohormone or chemical mixtures, that reportedly induced xylem vessel differentiation in other angiosperms Kubo et al, 2005;Kondo et al, 2016;Tan et al, 2018). Shoots were placed to ensure that search hyphae were in contact with the agarose medium.…”

“…Brassinosteroids also play a role in xylem vessel formation by promoting the transcription of HD-ZIP III transcription factor family genes, which are involved in establishing vascular patterning and determining cell fate (Ohashi-Ito et al, 2002;Fukuda, 2004). After the determination of cell fate in vascular tissue, the VASCULAR-RELATED NAC-DOMAIN (VND) family of transcription factors activates the expression of a set of genes required for xylem vessel cell differentiation (Kubo et al, 2005;Tan et al, 2018). The final process in xylem vessel differentiation is formation of patterned secondary cell walls (SCWs) and programmed cell death (PCD) (Fukuda, 2004).…”

Deep conservation of response element variants regulating plant hormonal responses

“…Amongst the genes containing a conserved TGTC GG variant, were the cell wall modifiers GH9B7 and GH9B5, previously shown to act downstream of auxin in lateral root formation, 35 as well as two EXPANSIN two mannose biosynthesis genes (Supplemental Figure 2B). TGTC CC was also found in association with the transcriptional factor WUSCHEL, which acts to maintain the growth of the shoot apical meristem 36 and VND2, which regulates xylem formation 37 .…”

Affinity‐based high‐resolution analysis of DNA binding by VASCULAR‐RELATED NAC‐DOMAIN7 via fluorescence correlation spectroscopy

“…The VND subgroup of this subfamily, comprising VND1–VND7, turns on both SCW deposition and PCD during vessel element differentiation (Kubo et al ., ; Zhou et al ., ; Endo et al ., ; Tan et al ., ), while the NST/SND subgroup, including NST1 and NST3/SECONDARY WALL‐ASSOCIATED NAC DOMAIN PROTEIN1 (SND1), is required for the development of interfascicular and xylary fibers, in which SCW deposition is strongly activated (Zhong et al ., ; Mitsuda et al ., ). Although all VNS members have the ability to induce ectopic SCW deposition through the upregulated expression of SCW‐related genes, only the VND subgroup can strongly induce the expression of PCD‐related genes, suggesting that the promoter regions of those genes contain sequences with specific affinity for VND1–VND7 (Yamaguchi et al ., ).…”