DlMYB1 positively regulates anthocyanin biosynthesis and contributes to red exocarp coloration in red-skinned longan

Red-skinned longan (Dimocarpus longan Lour.) varieties exhibit striking exocarp coloration and high potential market value. In this study, we characterized anthocyanin accumulation in the red-skinned longan RP1901 using high performance liquid chromatography (HPLC). The exocarp of RP1901 accumulated 264.2 μg g^-1 fresh weight (FW) of petunidin 3-O-glucoside (Pt3G) and 28.2 μg g^-1 FW of cyanidin 3-O-glucoside (Cy3G), whereas the common longan cultivar ShiXia showed no detectable levels of these pigments. Preliminary RNA-seq analysis suggested upregulation of anthocyanin pathway genes and DlMYB1 gene. RT-qPCR analysis indicated that F3'H, ANS, GST4, and DlMYB1 were significantly upregulated in the exocarp of RP1901 compared to ShiXia. Bioinformatic analysis revealed that DlMYB1 is structurally conserved across species but diverges by 12 amino acids from ShiXia (same species) and 16 amino acids from LcMYB1 in Litchi chinensis (different genus), indicating significant genetic variation between red-skinned and common longan varieties. Subcellular localization of a DlMYB1-eGFP fusion protein confirmed its nuclear localization, consistent with transcription factor function. Overexpression of DlMYB1 in Arabidopsis thaliana led to upregulated expression of AtPAL1, AtDFR, AtLDOX, and AtGST genes and significant accumulation of anthocyanin in transgenic plants. These findings demonstrate that DlMYB1 acts as a positive regulator of anthocyanin biosynthesis and plays a key role in the pigmentation of red-skinned longan RP1901.