Biochemical and molecular changes associated with heteroxylan biosynthesis in Neolamarckia cadamba (Rubiaceae) during xylogenesis.

Xianhai Zhao,Kunxi Ouyang,Shuai Zhao,Alan Marchant,Xiaomei Deng,Ai-Min Wu,Monika S Doblin,Lili Song,Juncheng Li,Xiao-Yang Chen,Wei Zeng,Antony Bacic,Siming Gan

doi:10.3389/fpls.2014.00602

Abstract

Wood, derived from plant secondary growth, is a commercially important material. Both cellulose and lignin assembly have been well studied during wood formation (xylogenesis), but heteroxylan biosynthesis is less well defined. Elucidation of the heteroxylan biosynthetic pathway is crucial to understand the mechanism of wood formation. Here, we use Neolamarckia cadamba, a fast-growing tropical tree, as a sample to analyze heteroxylan formation at the biochemical and molecular levels during wood formation. Analysis of the non-cellulosic polysaccharides isolated from N. cadamba stems shows that heteroxylans dominate non-cellulosic polysaccharides and increase with xylogenesis. Microsomes isolated from stems of 1-year-old N. cadamba exhibited UDP-Xyl synthase and xylosyltransferase activities with the highest activity present in the middle and basal stem regions. To further understand the genetic basis of heteroxylan synthesis, RNA sequencing (RNA-seq) was used to generate transcriptomes of N. cadamba during xylogenesis. The RNA-seq results showed that genes related to heteroxylan synthesis had higher expression levels in the middle and basal part of the stem compared to the apical part. Our results describe the heteroxylan distribution and heteroxylan synthesis trait in N. cadamba and give a new example for understanding the mechanism of heteroxylan synthesis in tropical tree species in future.

Highlights

Wood formation is a critical developmental process for all woody land plants and is important for mechanical support as well as water and mineral transport
THE SECONDARY THICKNESS OF XYLARY FIBERS VARIES IN DIFFERENT STEM SEGMENTS To systematically study heteroxylan synthesis occurring during secondary growth, three different stem segments representing discrete developmental stages with regard to secondary growth were isolated from the apical, middle, and basal regions of 1-year-old N. cadamba stems (Figure 1)
The quantitative real-time PCR (qRT-PCR) was used to confirm the results and conclude that almost all of these genes had higher expression levels in the middle and basal segments (Figures 7B,C). These results indicate that heteroxylan synthesis is active with the xylogenesis in N. cadamba

Summary

Introduction

Wood formation (xylogenesis) is a critical developmental process for all woody land plants and is important for mechanical support as well as water and mineral transport. Wood formation is a good model system to study plant cell wall biosynthesis at the DNA, RNA, and protein levels (Bailey, 1952; Plomion et al, 2001), but our understanding of xylogenesis is still elementary. Plant cell walls are predominantly composed of cellulose, non-cellulosic polysaccharides, and lignin which represent the most abundant renewable resource on Earth (Pauly and Keegstra, 2008). A β-1,4-glucan, accounts for the highest proportion of the cell wall (Pauly and Keegstra, 2010). Non-cellulosic polysaccharides account for more than a quarter of the dry mass of cell walls in dicot plants and are widely used in the food and pharmaceutical industries. The heteroxylan biosynthetic mechanism is not well understood

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Results

Conclusion