GSE62255
Deep sequencing analyses of Pine wood nematode Bursaphelenchus xylophilus microRNAs reveal distinct miRNA expression patterns during the pathological process of pine wilt disease
Bursaphelenchus xylophilus is known as the causative agent of pine wilt disease with complex life cycles. In this research, newly published Bursaphelenchus xylophilus genome data were employed to annotate its miRNAs based on deep sequencing technologies.  Four small RNA libraries derived from different infection stages of pine wilt disease were constructed and sequenced. Consequently, we obtained hundreds of evolutionarily conserved miRNAs as well as novel miRNA candidates. The analysis of miRNA expression patterns showed that most miRNAs were expressed at extraordinarily high levels during the middle stage of pine wilt disease. Subsequent stem-loop RT-PCR experiments were carried out to validate our results. Functional analysis proved that expression levels of miR-73 and miR-239 were mutually exclusive with their target GH45 cellulase genes., genes known to be responsible for the degradation of the pine cell walls.  In addition, another set of atypical miRNAs, termed mirtrons, were identified from B. xylophilus introns. This discovery has expanded the current knowledgebase of such splicing-derived miRNAs into B. xylophilus. Thus, our research has provided detailed characterization of B. xylophilus miRNAs expression patterns during the pathological process of pine wilt disease. The findings will contribute to more in-depth understanding of this devastating plant disease. Overall design: For the purposes of this study, we classified the pathogenic process associated with PWD into three stages in order to best characterize the expression patterns of microRNAs during the development of this devastating disease. The following describes the first stage (F): about seven days after pine trees are infected with PWNs, the tips of the pine needles begin to turn brown. Next, the middle stage (M) ensues approximately seven days later, when half of the needles on pine trees turn brown. The last stage (L) occurs another 10 days later and pine needles are complete browning. PWNs cultured on Botrytis cinerea grown on PDA medium served as the control stage (C).