Genome-wide transcriptional changes of ramie (Boehmeria nivea L. Gaud) in response to root-lesion nematode infection

Ramie fiber extracted from stem bark is one of the most important natural fibers. The root-lesion nematode (RLN) Pratylenchus coffeae is a major ramie pest and causes large fiber yield losses in China annually. The response mechanism of ramie to RLN infection is poorly understood. In this study, we identified genes that are potentially involved in the RLN-resistance in ramie using Illumina pair-end sequencing in two RLN-infected plants (Inf1 and Inf2) and two control plants (CO1 and CO2). Approximately 56.3, 51.7, 43.4, and 45.0 million sequencing reads were generated from the libraries of CO1, CO2, Inf1, and Inf2, respectively. De novo assembly for these 196 million reads yielded 50,486 unigenes with an average length of 8533 bp. A total of 24,820 (49.2%) genes were annotated for their function. Comparison of gene expression levels between CO and Inf ramie revealed 777 differentially expressed genes (DEGs). The expression levels of 12 DEGs were further confirmed by real-time quantitative PCR (qRT-PCR). Pathway enrichment analysis showed that three pathways (phenylalanine metabolism, carotenoid biosynthesis, and phenylpropanoid biosynthesis) were strongly influenced by RLN infection. A series of candidate genes and pathways that may contribute to the defense response against RLN in ramie will be helpful for further improving resistance to RLN infection. (C) 2014 Published by Elsevier B.V.