Sun Quan, He Zhengchen, Wei Ranran, Ye Junli, Chai Lijun, Cheng Yunjiang, Xu Qiang, Deng Xiuxin
National Key Laboratory for Germplasm Innovation and Utilization of Horticultural Crops, Huazhong Agricultural University, Wuhan 430070, China.
National Research Center for Apple Engineering and Technology, Shandong Collaborative Innovation Center of Fruit & Vegetable Quality and Efficient Production, College of Horticulture Science and Engineering, Shandong Agricultural University, Taian, Shandong 271018, China.
Plant Cell. 2024 Dec 23;37(1). doi: 10.1093/plcell/koaf010.
The reddish apocarotenoid β-citraurin, produced by CAROTENOID CLEAVAGE DIOXYGENASE 4b (CsCCD4b), is responsible for peel reddening in citrus (Citrus spp.). Ethylene induces the characteristic red color of citrus peel, but the underlying molecular mechanism remains largely unclear. Here, we identified red peel regulator 1 (CsRP1), a trihelix transcriptional activator that regulates ethylene-induced peel reddening by directly binding to a key V-myb avian myeloblastosis viral oncogene homolog (MYB)-binding site in the CsCCD4b promoter, thus activating its transcription. Furthermore, 2 drought-responsive cis-elements in the CsRP1 promoter are bound by the ethylene response factor ethylene response factor 25 (CsERF25). We reconstructed the CsERF25-CsRP1-CsCCD4b transcriptional regulatory cascade through transient expression of CsERF25 and CsRP1 in citrus peel and via stable transformation of citrus calli. In this cascade, CsERF25 expression was induced by ethylene to activate CsRP1 expression, and then, CsRP1 directly induced CsCCD4b transcription to catalyze β-citraurin biosynthesis. CsRP1 and CsERF25 also bound to the promoters of other carotenogenic genes and induced their transcription, thereby promoting β-citraurin accumulation. Collectively, our findings reveal a complex regulatory network modulating ethylene-induced citrus peel reddening and provide innovative strategies for improving the nutritional and esthetic values of citrus and other fruit crops.
由类胡萝卜素裂解双加氧酶4b（CsCCD4b）产生的微红的脱辅基类胡萝卜素β-柠乌素，是柑橘（柑橘属）果皮变红的原因。乙烯诱导柑橘果皮呈现特征性红色，但其潜在的分子机制仍不清楚。在此，我们鉴定出红色果皮调控因子1（CsRP1），这是一种三螺旋转录激活因子，通过直接结合CsCCD4b启动子中的关键V-myb禽成髓细胞瘤病毒癌基因同源物（MYB）结合位点来调控乙烯诱导的果皮变红，从而激活其转录。此外，CsRP1启动子中的2个干旱响应顺式元件被乙烯响应因子乙烯响应因子25（CsERF25）结合。我们通过在柑橘果皮中瞬时表达CsERF25和CsRP1以及通过柑橘愈伤组织的稳定转化，重建了CsERF25-CsRP1-CsCCD4b转录调控级联。在这个级联中，乙烯诱导CsERF25表达以激活CsRP1表达，然后，CsRP1直接诱导CsCCD4b转录以催化β-柠乌素生物合成。CsRP1和CsERF25还与其他类胡萝卜素生成基因的启动子结合并诱导其转录，从而促进β-柠乌素积累。总的来说，我们的研究结果揭示了一个调节乙烯诱导的柑橘果皮变红的复杂调控网络，并为提高柑橘和其他水果作物的营养和美学价值提供了创新策略。
