Small RNA and Degradome Sequencing Reveal Roles of miRNAs in the Petal Color Fading of Crabapple.

The crabapple is an important woody ornamental plant. The fading of petals during its development significantly affects their ornamental value. Petal color is related to anthocyanin content and miRNAs play an important role in the post-transcriptional regulation of anthocyanin synthesis. However, the mechanisms underlying miRNA regulation of petal fading have rarely been studied. Transcriptome and small RNA sequencing of petals from the blooming phases of . 'Indian Summer' varieties S1 (small bud), S2 (initial-flowering), and S3 (late-flowering) allowed us to identify 230 known miRNAs and 17 novel miRNAs, including 52 differentially expressed miRNAs which targeted 494 genes and formed 823 miRNA-target pairs. Based on the target gene annotation results, miRNA-target pairs were screened that may be involved in the fading process of crabapple petals through three different pathways: anthocyanin synthesis, transport, and degradation, involving mcr-miR858-\ and mcr-miR396- inhibiting anthocyanin synthesis; mcr-miR167, mcr-miR390, mcr-miR535, and mcr-miR858 inhibiting anthocyanin transport from the cytoplasm to the vacuole by targeting ABC transporter genes (, , , and ); and mcr-miR398 targeting the superoxide dismutase genes ( and ) to accelerate anthocyanin degradation. These findings offer a novel approach to understanding the mechanism of petal fading and serve as a reference for other plants with floral fading.