SmMYB44, a transcriptional repressor, negatively regulates anthocyanin biosynthesis in eggplant (Solanum melongena L.)

Anthocyanins are the main flavonoid secondary metabolites in plants. They not only protect plants against diverse biotic and abiotic stresses but also provide human health benefits. In this study, SmMYB44, an R2R3-MYB transcription factor, was identified from the photosensitive eggplant cultivar ‘Lanshan Hexian’. SmMYB44 was localized in the nucleus, induced by light, and expressed specifically in peel, petals and roots. Overexpression of SmMYB44 in transgenic eggplant significantly inhibited anthocyanin accumulation, whereas virus-induced gene silencing of SmMYB44 in fruit peels markedly increased anthocyanin content and upregulated the transcription levels of key biosynthetic genes SmCHS and SmF3H . Furthermore, Agrobacterium-mediated CRISPR/Cas9 editing of NtMYB44 in tobacco cultivar K326, with an editing efficiency of 84.62%, markedly suppressed NtMYB44 transcription and strongly upregulated anthocyanin biosynthetic genes in tobacco petals, resulting in a 2.5- to 4.2-fold increase in anthocyanin content and significantly darker petal color. Yeast one-hybrid and dual-luciferase assays confirmed that SmMYB44 could directly bind to the promoters of SmCHS and SmF3H and repress their transcriptional activity. In addition, SmMYB44 physically interacts with the co-repressor SmTPL to form a transcriptional repressive complex. Although SmTPL alone has no capacity to activate SmCHS and SmF3H transcription, it cooperates with SmMYB44 to strengthen the repression of target gene promoters. Collectively, SmMYB44 negatively regulates light-induced anthocyanin biosynthesis in eggplant through direct transcriptional repression of key structural genes and synergistic inhibition through physical association with the co-repressor SmTPL.