Jasmonate activates a CsMPK6-CsMYC2 module that regulates the expression of β-citraurin biosynthetic genes and fruit coloration in orange (Citrus sinensis)

Abstract

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). Although jasmonates are known to regulate the biosynthesis and accumulation of carotenoids, their effects on β-citraurin biosynthesis in citrus fruit remain unclear. Here, we determined that treatment with methyl jasmonate (MeJA) significantly promotes fruit coloration and β-citraurin production in ‘Newhall’ orange. A MeJA treatment induced the expression of CsMYC2, which encodes a transcription factor that serves as a master regulator of jasmonate responses. 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. 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. 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.

Improvement of Panax notoginseng saponin accumulation triggered by methyl jasmonate under arbuscular mycorrhizal fungi

“…The concentrations of JA, MeJA, JA-Ile and OPDA in our study increased significantly under the addition of MeJA ( Figure 3 ). Similar results were confirmed by the reports of Yue et al. (2023) and Mandal et al.…”

Involvement of Transcription Factors and Regulatory Proteins in the Regulation of Carotenoid Accumulation in Plants and Algae

“…32 The master regulator of jasmonate responses, CsMYC2 (belonging to bHLH family) could activate the expression of the CsCCD4b gene responsible for β-citraurin biosynthesis and CsPSY, CsLCYb, and CsBCH genes responsible for fruit peel coloration and promoted expression of the mitogen-activated protein kinase gene CsMPK6. 33 In turn, CsMPK6 interacted with CsMYC2 to decrease the promoter-binding activity of CsMYC2 to its target promoters, 33 suggesting that negative feedback regulation attenuates jasmonate signaling during the jasmonate-induced coloration of citrus fruit.…”

Regulation of Chlorophyll and Carotenoid Metabolism in Citrus Fruit During Maturation and Regreening

“…Rehman et al [60] reported that the preharvest spray application of MeJA induced carotenoid accumulation and accelerated fruit coloration in flavedo of M7 Navel orange. In the study of Yue et al [61], it was found that the postharvest exogenous MeJA treatment promoted the β-citraurin production and fruit coloration in Newhall orange by inducing the expression of the transcription factor MYC2, which substantially activated the expression of the key β-citraurin biosynthetic genes (CCD4b, PSY, LCYB, and HYb). Different from the flavedo, MeJA negatively regulated carotenoid accumulation of the juice sacs of citrus fruit.…”