De novo assembly of transcriptome and genome-wide identification reveal GA(3) stress-responsive WRKY transcription factors involved in fiber formation in jute (Corchorus capsularis)

BACKGROUND: WRKY is a group of transcription factors (TFs) that play a vital role in plant growth, development, and stress tolerance. To date, none of jute WRKY (CcWRKY) genes have been identified, even if jute (Corchorus capsularis) is one of the most important natural fiber crops in the world. Little information about the WRKY genes in jute is far from sufficient to understand the molecular mechanism of bast fiber biosynthesis. RESULTS: A total of 244,489,479 clean reads were generated using Illumina paired-end sequencing. De novo assembly yielded 90,982 unigenes with an average length of 714 bp. By sequence similarity searching for known proteins, 48,896 (53.74%) unigenes were annotated. To mine the CcWRKY TFs and identify their potential function, the search for CcWRKYs against the transcriptome data of jute was performed, and a total of 43 CcWRKYs were identified in this study. The gene structure, phylogeny, conserved domain and three-dimensional structure of protein were analyzed by bioinformatics tools of GSDS2.0, MEGA7.0, DNAMAN5.0, WebLogo 3 and SWISS-MODEL respectively. Phylogenetic analysis showed that 43 CcWRKYs were divided into three groups: I, II and III, containing 9, 28, and 6 members respectively, according to the WRKY conserved domain features and the evolution analysis with Arabidopsis thaliana. Gene structure analysis indicated that the number of exons of these CcWRKYs varied from 3 to 11. Among the 43 CcWRKYs, 10, 2, 2, and 14 genes showed higher expression in leaves, stem sticks, stem barks, and roots at the vigorous vegetative growth stage, respectively. Moreover, the expression of 21 of 43 CcWRKYs was regulated significantly with secondary cell wall biosynthesis genes using FPKM and RT-qPCR by GA(3) stress to a typical GA(3) sensitive dwarf germplasm in comparison to an elite cultivar in jute. The Cis-element analysis showed that promoters of these 21 CcWRKYs had 1 to 4 cis-elements involved in gibberellin-responsiveness, suggesting that they might regulate the development of bast fiber in response to GA(3) stress. CONCLUSIONS: A total of 43 CcWRKYs were identified in jute for the first time. Analysis of phylogenetic relationship and gene structure revealed that these CcWRKYs might have a functional diversity. Expression analysis showed 21 TFs as GA(3) stress responsive genes. The identification of these CcWRKYs and the characterization of their expression pattern will provide a basis for future clarification of their functions in bast fiber development in jute.