背景回顾：Carotenoids are natural pigments that influence the color of citrus fruit. The red-colored carotenoid β-citraurin is responsible for the peel color in ‘Newhall’ orange (Citrus sinensis). 

提出问题：Although jasmonates are known to regulate the biosynthesis and accumulation of carotenoids, their effects on β-citraurin biosynthesis in citrus fruit remain unclear. 

主要发现：Here, we determined that treatment with methyl jasmonate (MeJA) significantly promotes fruit coloration and β-citraurin production in ‘Newhall’ orange. 

结果1-MeJA诱导MYC2的表达：A MeJA treatment induced the expression of CsMYC2, which encodes a transcription factor that serves as a master regulator of jasmonate responses.   

结果2-MYC2激活类胡萝卜素生物合成相关基因的表达：CsMYC2 bound the promoter of the gene that encodes carotenoid cleavage dioxygenase 4b (CsCCD4b), the key gene for β-citraurin biosynthesis, and the promoters of genes that encode phytoene synthase (CsPSY), lycopene β-cyclase (CsLCYb), and β-carotene hydroxylase (CsBCH) and induced their expression. 

结果3-MYC2-MPK6互作：In addition, CsMYC2 promoted CsMPK6 expression. Notably, we found that CsMPK6 interacted with CsMYC2 and that this interaction decreased the stability and DNA-binding activity of CsMYC2.

结论：Thus, we conclude that negative feedback regulation attenuates JA signaling during the jasmonate-induced coloration of citrus fruit. Together, our findings indicate that jasmonates induce β-citraurin biosynthesis in citrus by activating a CsMPK6-CsMYC2 cascade, thereby affecting fruit coloration.

类胡萝卜素是一种天然色素，能够影响柑橘果实的颜色。红色的胡萝卜素β-citraurin是纽荷尔脐橙果皮颜色的主要着色色素。茉莉酸类物质（JAs）被认为参与了类胡萝卜素生物合成和积累的调控，但是其对于β-citraurin生物合成的效应还不清楚。本文中，作者发现通过茉莉酸甲酯（MeJA）处理能够显著促进纽荷尔脐橙的果实着色以及β-citraurin含量。MeJA处理会诱导转录因子CsMYC2的表达，而后者正是JA响应的主要调节子。CsMYC2能够结合到类胡萝卜素裂解双加氧酶（CsCCD4b）、八氢番茄红素合酶（PSY）、番茄红素β-环化酶（CsLCYb）以及β-胡萝卜素羟化酶（CsBCH）编码基因的启动子上，诱导这些基因的表达。另外，CsMYC2还能够促进CsMPK6的表达。尤其是，作者发现CsMPK6与CsMYC2互作，从而降低CsMYC2蛋白的稳定性和结合DNA的活性。因此，作者提出在JA诱导的柑橘果实着色过程中，存在一个负反馈调节作用于JA信号转导的减弱。综上，本文的研究结果揭示了JAs通过激活一个CsMPK6-CsMYC级联诱导β-citraurin的生物合成，从而影响柑橘的果实着色。

** 邓秀新 **