BoOFP6 Negatively Regulates Glucosinolates Accumulation in Broccoli Sprouts by Cytoplasmic Sequestration of BoMYB34-3

Broccoli (Brassica oleracea L.) sprouts have been popular among consumers for its excellent nutritional value. Glucosinolates (GSLs) and their degradation products, which are abundant in cruciferous vegetables, are linked to the anticancer activity. This study investigated the GSLs and derivatives accumulation characteristic in different broccoli sprout varieties and identified two GSLs rich varieties, B001 and B003. Transcriptome analysis indicated that BoMYB34-3 contributed to the high GSLs content in B001. Overexpressing BoMYB34-3 in broccoli cotyledons significantly increased GSLs and derivatives levels. Nuclear-localised BoMYB34-3 bound to the promoters of GSLs biosynthesis genes and activated their expression to promote GSLs accumulation. An OVATE family protein 6 (BoOFP6) was identified as an interacting partner of BoMYB34-3. Overexpressing BoOFP6 significantly suppressed GSLs accumulation and the expression level of related genes, whereas its silencing markedly promoted these processes. BoOFP6 exerted its negative regulatory function by mediating the re-localisation of BoMYB34-3 to the cytoplasm rather than by directly inhibiting GSLs biosynthesis related genes. This regulatory process could be influenced by environmental cues, including blue light, mechanical damage, salt stress and drought stress. This study provides insights into GSLs biosynthetic pathway and a foundation for breeding strategies to enhance health-promoting compounds in broccoli sprouts.