Comparative transcriptomics of stem bark reveals genes associated with bast fiber development in Boehmeria nivea L. Gaud (ramie)

Abstract

Background: Boehmeria nivea L. Gaud (Ramie) produces one of the longest natural fibers in nature. The bark of ramie mainly comprises of the phloem tissue of stem and is the raw material for fiber. Therefore, identifying the molecular regulation of phloem development is important for understanding of bast fiber biosynthesis and improvement of fiber quality in ramie.Results: In this study, we collected top bud (TB), bark from internode elongating region (ER) and bark from internode fully elongated region (FER) from the ramie variety Zhongzhu No. 1. Histological study indicated that these samples contain phloem tissues at different developmental and maturation stages, with a higher degree of maturation of phloem tissue in FER. RNA sequencing (RNA-seq) was performed to identify differentially expressed genes (DEGs) in these three samples. The de novo transcriptome was assembled and unigenes were identified. The DEGs among TB, ER and FER were analyzed, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) studies revealed clear differences in gene expression between ER and FER. Some unigenes for secondary cell wall biosynthesis were up-regulated in both ER and FER, while unigenes for some cell wall components or cell wall modifications showed differential expression between ER and FER. In addition, ethylene activating pathway and gibberellins biosynthesis showed distinct regulation and coincided with the developmental stages of the samples. Conclusions: Both morphological study and gene expression analysis supported a burst of phloem and vascular developmental processes during the fiber maturation in the ramie stem, and the phytohormon ethylene and gibberellin are likely to be involved in this process. Our findings provide novel insights into the phloem development and fiber maturation in ramie, which could be useful for fiber improvement in ramie and other fiber crops.

FIBexDB: a new online transcriptome platform to analyze development of plant cellulosic fibers

“…Each model system has its advantages: flax fiber bundles can be easily isolated, giving the unique possibility to analyze the distinct single cell type at the certain developmental stage. Some transcriptomic studies have been conducted in fiber-containing samples of other fiber crops (Guerriero et al, 2017;Xie et al, 2020); however, datasets for purified fibers are not available for any of these species. In poplar tension wood, the development of tertiary cell walls occurs in fibers as a part of joint reactions of several cell types.…”