Identification of microRNAs and their target genes related to needle discoloration of evergreen tree Chinese cedar (Cryptomeria fortunei) in cold winters.

Abstract

Comparative analysis of miRNAs and their gene targets between the evergreen and yellowish-brown Cryptomeria fortunei phenotypes in cold winters suggests a possible role of miRNA-regulated pathways in needle color. Cryptomeria fortunei (Chinese cedar) is a conifer tree of considerable economic, ornamental and ecological importance. Despite the evergreen nature of C. fortunei, most needles turn yellowish- or reddish-brown in winter. The roles of microRNAs (miRNAs) in regulating pigment biosynthesis in color-leafed plants have been widely investigated. However, whether or not an miRNA-mediated staged discoloration mechanism exists in evergreen C. fortunei is currently unknown. In this study, we deciphered the microRNAs landscape in overwintering C. fortunei needles using high-throughput sequencing. A total of 517 known and 212 novel miRNA mature/star sequences, including 233 differentially expressed miRNAs, were identified. Based on integrated transcriptome and miRNA analysis, 2702 target unigenes of the miRNAs were predicted and these targets were significantly enriched in pigment-related biosynthesis pathways. A miRNA-target pigment biosynthesis regulatory network was then constructed, and its module miRNA (ath-miR858b, aly-miR858-3p, cme-miR828 and novel33_mature)-MYBs (v-myb avian myeloblastosis viral oncogene homolog) appeared to be a key factor regulating needle discoloration in C. fortunei. These miRNA-MYBs were further confirmed by degradome sequencing. Overall, these findings provide new insight into the posttranscriptional regulatory mechanism of leaf/needle discoloration in gymnosperms and may contribute to the miRNA-mediated genetic improvement of evergreen C. fortunei needles.