Identification, characterization, and transcription analysis of xylogen-like arabinogalactan proteins in rice (Oryza sativa L.).

Heming Zhao,Haoli Ma,Huandong Qi,Tengfei Ma,Jie Zhao

doi:10.1186/s12870-014-0299-y

Abstract

BackgroundXylogen, a chimeric arabinogalactan protein containing a non-specific lipid transfer protein domain, can promote xylem cell differentiation. No comprehensive study has been carried out on the XYLP gene family in rice. As a first step in research on this gene family and as a useful strategy in general, a genome-wide analysis of the OsXYLP gene family is thus needed.ResultsIn this study, we identified 21 XYLP genes from the rice genome and comprehensively analyzed their protein structures, phylogenetic relationships, chromosomal locations, and gene duplication status. Our results indicate that gene duplication has played major roles in the expansion of the OsXYLP gene family. We used expressed sequence tag, microarray, massively parallel signature sequencing, and quantitative real-time PCR data to analyze OsXYLP gene expression during various developmental stages and under abiotic stress conditions. We found that many OsXYLP genes are abundantly expressed in vascular tissues and seeds, with some genes regulated under hormonal or abiotic stresses. In addition, we identified knockout mutants of OsXYLP7 and OsXYLP16 and discovered that the mutant xylp7 has a defect in stem height.ConclusionsWe analyzed expression profiles of 21 XYLP genes and characterized the structures and evolutionary relationships of their proteins. Our results demonstrate that the rice XYLP gene family may play roles in plant vascular system development and hormone signaling. Among the 21 detected OsXYLPs, 19 are newly identified genes encoding arabinogalactan proteins. Our results provide comprehensive insights that will assist future research on the biological functions of the rice XYLP gene family.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0299-y) contains supplementary material, which is available to authorized users.

Highlights

Xylogen, a chimeric arabinogalactan protein containing a non-specific lipid transfer protein domain, can promote xylem cell differentiation
After confirming the presence of non-specific lipid-transfer proteins (nsLTPs)-like domains, Arabinogalactan proteins (AGPs)-like regions, and AG-type glycomodules and removing redundant sequences, we identified 21 OsXYLPs in rice (Table 1)
OsLTPL1 was first isolated as a β-glucosyl Yariv reagent (β-GlcY)-reactive arabinogalactan protein; and OsLTPL1 and OsXYLP9 were identified as nsLTP-like AGPs

Summary

Introduction

A chimeric arabinogalactan protein containing a non-specific lipid transfer protein domain, can promote xylem cell differentiation. Arabinogalactan proteins (AGPs) are a class of extracellular glycoproteins consisting of a core protein backbone and diverse type-II arabinogalactan (AG) polysaccharide chains made up of galactan and arabinose [1,2,3,4]. The lipid-binding properties of nsLTPs are derived from a unique structure: a region of eight strictly conserved cysteine residues. Xylogen is secreted from differentiating vascular cells and promotes the transformation of adjacent undifferentiated cells into TEs; it has a unique structure including AGP domains and an nsLTP domain, as typical structure of chimeric AGPs [11]. In a previous bioinformatic analysis of xylogen-type proteins in Arabidopsis [12], 13 AtXYLP (xylogen-like protein) genes with significant similarity to ZeXYP1 were identified and their expression profiles were analyzed

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Conclusion