The Xylem and Phloem Transcriptomes from Secondary Tissues of the Arabidopsis Root-Hypocotyl  

Abstract

The growth of secondary xylem and phloem depends on the division of cells in the vascular cambium and results in an increase in the diameter of the root and stem. Very little is known about the genetic mechanisms that control cambial activity and the differentiation of secondary xylem and phloem cell types. To begin to identify new genes required for vascular cell differentiation and function, we performed genome-wide expression profiling of xylem and phloem-cambium isolated from the root-hypocotyl of Arabidopsis (Arabidopsis thaliana). Gene expression in the remaining nonvascular tissue was also profiled. From these transcript profiles, we assembled three sets of genes with expression significantly biased toward xylem, phloem-cambium, or nonvascular tissue. We also assembled three two-tissue sets of genes with expression significantly biased toward xylem/phloem-cambium, xylem/nonvascular, or phloem-cambium/nonvascular tissues. Localizations predicted by transcript profiles were supported by results from promoter-reporter and reverse transcription-polymerase chain reaction experiments with nine xylem- or phloem-cambium-biased genes. An analysis of the members of the phloem-cambium gene set suggested that some genes involved in regulating primary meristems are also regulators of the cambium. Secondary phloem was implicated in the synthesis of auxin, glucosinolates, cytokinin, and gibberellic acid. Transcript profiles also supported the importance of class III HD ZIP and KANADI transcription factors as regulators of radial patterning during secondary growth, and identified several members of the G2-like, NAC, AP2, MADS, and MYB transcription factor families that may play roles as regulators of xylem or phloem cell differentiation and activity.

Expression of DOF genes identifies early stages of vascular development in Arabidopsis leaves

“…1). Detailed expression data for five of these nine DOF genes are already available and support their vascular-specific expression in roots and other organs (Gualberti et al, 2002;Skirycz et al, 2006;Ward et al, 2005;Zhao et al, 2005), suggesting that preselecting vascular gene expression profiles based on root expression patterns from whole-genome microarray datasets may be an effective criterion. Here we investigated leaf expression of the remaining four DOF genes 2.…”

Arabidopsis Type I Proton-Pumping Pyrophosphatase Expresses Strongly in Phloem, Where It Is Required for Pyrophosphate Metabolism and Photosynthate Partitioning

“…S4). DOF2 elements (AAAG or CTTT) are the core binding sites for DOF transcription factors (Noguero et al, 2013) that are positive regulators required in the formation and functioning of vascular tissues, including those of Arabidopsis (Ward et al, 1998;Zhao et al, 2005;Le Hir and Bellini, 2013). DOF2 elements are also present in the essential 241-bp SUC2 promoter fragment that drives phloem-specific SUC2 expression in Arabidopsis (Schneidereit et al, 2008), and the 244-bp promoter is sufficient to drive AVP1 expression in the phloem (Fig.…”

Binding Properties of the N-Acetylglucosamine and High-Mannose N-Glycan PP2-A1 Phloem Lectin in Arabidopsis

“…In both species, these genes were found to be expressed specifically in the companion cell-sieve element complex . PP2 transcripts have also been found in phloem transcriptomes from various species (Ivashikina et al, 2003;Vilaine et al, 2003;Schrader et al, 2004;Zhao et al, 2005;Le Hir et al, 2008) and more recently in the companion cell translatome in Arabidopsis (Mustroph et al, 2009).…”