Class III HD-ZIPs govern vascular cell fate: an HD view on patterning and differentiation

Auxin-mediated regulation of vascular patterning in Arabidopsis thaliana leaves

“…Moreover, there is no clear correlation between changes in the DR5 expression pattern, indicating a high level of auxin and the auxin response, and the progressive extension of the ATHB8 expression domains (Fig. 2c, e), nor is there correlation between DR5 expression patterns and other transcription factors from the HD-ZIP III family (Ramachandran et al 2017). As such, it has been suggested that some factors other than auxin may participate in the activation of ATHB8 and other genes of the HD-ZIP III family (Ramachandran et al 2017).…”

“…It is assumed that ATHB8 has different functions during each of these stages (Baima et al 2001; Donner et al 2010; Ramachandran et al 2017). During the preprocambial stage, its activity probably relates to vascular pattern formation, whereas during the procambial stage, it may be involved in the regulation of meristematic cell divisions and early xylem specification, acting simultaneously as a negative regulator of xylem differentiation (Baima et al 2001; Scarpella et al 2004; Prigge et al 2005; Donner et al 2009; Ramachandran et al 2017). …”

“…2c, e), nor is there correlation between DR5 expression patterns and other transcription factors from the HD-ZIP III family (Ramachandran et al 2017). As such, it has been suggested that some factors other than auxin may participate in the activation of ATHB8 and other genes of the HD-ZIP III family (Ramachandran et al 2017). The lack of a clear correlation between the DR5 and ATHB8 expression patterns may also be because the AuxRE present in the DR5 synthetic promoter and the ARF-binding sequence in ATHB8 are not identical (Donner et al 2009).…”

Realizing pipe dreams – a detailed picture of vascular development

“…However, the wiring within these models is varied. For example, that put forward by Muraro et al (2014) also incorporates an interaction between the class III homeodomain-leucine zipper (HD-Zip III) transcription factor PHABULOSA (PHB) and cytokinin, an interaction explored in this special issue (Ramachandran et al , 2017). In all cases the models make novel predictions that have subsequently been validated, so certainly all expand our understanding of early vascular development.…”

“…In xylem initials, this differentiation is controlled by a very large gene regulatory network (Taylor-Teeples et al , 2015), in which HD-Zip III genes are prominent (Zhong and Ye, 1999; Baima et al , 2001; Ohashi-Ito et al , 2002; Ochando et al , 2008; Baima et al , 2014; Du et al , 2015). Ramachandran et al (2017) explore the role that HD-Zip III genes play in vascular patterning in many contexts, including in early patterning of the root xylem axis, radial patterning of vascular bundles in the stem, and regulation of cell wall polymer deposition in the xylem. In comparison to xylem specification, less is known about how the phloem cell types are specified and differentiated.…”