BrmiR828 Targets BrPAP1, BrMYB82, and BrTAS4 Involved in the Light Induced Anthocyanin Biosynthetic Pathway in Brassica rapa

Comprehensive research in various plants shows that the metabolic pathway of anthocyanin biosynthesis is affected by environmental factors and regulated by microRNAs through post-transcriptional regulation. In seedlings of Brassica rapa Tsuda, the accumulation of anthocyanin is induced by light. However, the roles of BrmiR828 in the light-induced synthesis of anthocyanin in Brassica rapa remain to be explored. Here, a primary transcript of BrmiR828 was identified to be located on the chromosomes of the A03 sub-genome. Five candidate MYB family genes were predicted as targets of BrmiR828 in the database of Brassica rapa (BRAD, V1.1) by using psRNATarget. The transcript abundance of mature BrmiR828 was reduced in seedlings of Brassica rapa Tsuda under blue light irradiation comparing with dark treatment. However, Real-time PCR showed the transcript level of the five candidate targets, Bra004162, Bra022602, Bra001917, Bra029113, and Bra039763 was up-regulated when the seedlings exposed to blue or UV-A light. Trans-acting siRNA gene 4 (BrTAS4) was also identified to have a higher transcript level under blue and UV-A light irradiation than that in dark treatment. RNA ligase mediated 5'amplification of cDNA ends (RLM-5' RACE) showed that BrmiR828 can splice the mRNA of Bra039763, Bra022602, and BrTAS4 on binding sites. Phylogenetic analysis of candidate BrMYBs targets along with MYBs from Arabidopsis thaliana showed that Bra039763, Bra004162, Bra001917, Bra029113, and Bra022602 are classified to the same group with AtMYB75, AtMYB114, AtMYB90, AtMYB113, and AtMYB82 which are involved in the anthocyanin biosynthetic pathway. As a result, light-induced down-regulation of BrmiR828 can target BrTAS4, BrPAP1 (Bra039763), MYB82 (Bra022602) to negatively regulate their transcript levels leading to the accumulation of MYB transcription factors that positively regulate anthocyanin biosynthesis in light-exposed seedlings of Brassica rapa.

Keywords: Brassica rapa; anthocyanin biosynthesis; gene expression; miR828; regulation.