Bifurcation of StCRY1-StHY5 axis orchestrates blue light-enhanced glycoalkaloid and chlorophyll accumulation in potato tubers

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Potato, the fourth largest food crop in the world, stores nutrients in underground tubers. However, light exposure induces tuber accumulation of chlorophyll and toxic steroidal glycoalkaloids (SGAs), an unwanted trait called tuber greening causes potato quality decline and parts of tuber inedible. Despite progress in enzymatic cascades governing SGAs biosynthesis, the regulatory scheme of SGAs and chlorophyll metabolism in light-exposed tubers persists as a critical knowledge gap. Here, we identify the blue light receptor StCRY1 plays a predominant role in light-induced tuber greening and SGAs elevation, which functions as a light-controlled transcriptional switch for genes involved in SGAs and chlorophyll biosynthesis. We show that transcription factor StHY5 acts downstream of StCRY1 to co-regulates both chlorophyll and SGAs metabolism. However, StMYB4, a transcription factor regulated by StHY5, promotes SGAs synthesis by directly binding to SGA biosynthetic genes without affecting chlorophyll homeostasis. Furthermore, StCRY1 employs a dual strategy by modulating StMYB4 expression and physically interaction with StMYB4 to regulate its transcriptional activity. Collectively, these findings uncover a modularly coordinated control of SGAs accumulation and chlorophyll biosynthesis by bifurcation of StCRY1-StHY5 axis, providing a promising strategy to concurrently curb light-induced tuber greening and glycoalkaloids accumulation.