Overexpression of microRNA828 reduces anthocyanin accumulation in Arabidopsis

Plant microRNAs (miRNAs) are RNAs of 20-22 nucleotides in length with sequence complementarities to specific mRNAs that are targeted for either cleavage or translational repression. They play critical regulatory roles in plant growth and development. In this study, the functionality of miR828 in the regulation of anthocyanin biosynthesis has been investigated. RNA blotting analysis has confirmed the presence of a conserved 22 nucleotide miR828 in both dicot and monocot plants. Moreover, it has revealed that miR828 is constitutively expressed in different tissues of Arabidopsis. Subsequently, a 35S:pre-miR828 construct has been created and transformed into Arabidopsis. Expression analysis has shown that levels of pre-miR828 and mature miR828 transcripts are increased, while levels of MYB75, MYB90, and MYB113 transcripts, encoding MYB transcription factors that positively regulate anthocyanin biosynthesis, are repressed in transgenic plants. As a result, anthocyanin levels are reduced, as are transcription levels of genes that are directly involved in anthocyanin biosynthesis, including PAL, CHS, CHI, F3H, F3'H, DFR, and LDOX. In addition, overexpression of miR828 in Arabidopsis inhibits transcription of yet another MYB factor, MYB82, indicating that MYB82 is likely to be involved in the anthocyanin biosynthesis pathway.