By Pengtao Yue
Background: Beautiful, bright peel colors attract animals to help disperse seeds and are preferred by consumers. In agricultural production, citrus fruit often suffers from uneven coloration and poor development of color in the fruit peel, which limits fruit value. Carotenoids are natural pigments in plants and the red carotenoid β-citraurin is essential for the peel coloration of ‘Newhall’ orange fruit. Although many signaling pathways are linked to the regulation of carotenoid biosynthesis, how β-citraurin biosynthesis is regulated during citrus fruit development and maturation is still poorly understood, which hampers the development of management strategies for improving citrus fruit coloration. Jasmonates regulate carotenoid biosynthesis, but their role in citrus fruit coloration is unknown.
Question: What are the detailed mechanisms by which jasmonates regulate β-citraurin biosynthesis?
Findings: We found that exogenous methyl jasmonate (MeJA) treatment of ‘Newhall’ orange fruit promoted β-citraurin accumulation and fruit peel coloration. The jasmonate signaling master transcription factor CsMYC2 bound promoters of β-citraurin biosynthetic genes and activated their expression and promoted expression of the MAP kinase gene CsMPK6. In turn, CsMPK6 interacted with CsMYC2 to decrease the promoter binding activity of CsMYC2 to its target promoters. CsMPK6 also phosphorylated CsMYC2 to accelerate its degradation and thus, attenuated the jasmonate response for citrus to prevent the fruit from overreacting to jasmonates.
Next steps: An important task for next step is to explore whether other signaling pathways interact with jasmonates to co-regulate β-citraurin biosynthesis. With that work, we will investigate whether CsMYC2 serves as a mediator to bridge jasmonate signaling with other signaling pathways in regulating citrus coloration.
Pengtao Yue, Zhenghua Jiang, Quan Sun, Ranran Wei, Yingzi Yin, Zongzhou Xie, Robert M. Larkin, Junli Ye, Lijun Chai, Xiuxin Deng. (2023). Jasmonate activates a CsMPK6-CsMYC2 module that regulates the expression of β-citraurin biosynthetic genes and fruit coloration in orange (Citrus sinensis). https://doi.org/10.1093/plcell/koac363