Transcription factors MdMYC2 and MdMYB85 interact with ester aroma synthesis gene MdAAT1 in apple.

Volatile esters in apple (Malus domestica) fruit are the critical aroma components determining apple flavor quality. While the exact molecular regulatory mechanism remains unknown, jasmonic acid (JA) plays a crucial role in stimulating the synthesis of ester aromas in apples. In our study, we investigated the effects of methyl jasmonate (MeJA) on the production of ester aroma in apples. MeJA treatment significantly increased ester aroma synthesis, accompanied by the upregulation of several genes involved in the jasmonate pathway transduction. Specifically, expression of the gene MdMYC2, which encodes a transcription factor associated with the jasmonate pathway, and the R2R3-MYB transcription factor gene MdMYB85 increased upon MeJA treatment. Furthermore, the essential gene ALCOHOL ACYLTRANSFERASE 1 (MdAAT1), encoding an enzyme responsible for ester aroma synthesis, showed increased expression levels as well. Our investigation revealed that MdMYC2 and MdMYB85 directly interacted with the promoter region of MdAAT1, thereby enhancing its transcriptional activity. In addition, MdMYC2 and MdMYB85 directly bind their promoters and activate transcription. Notably, the interaction between MdMYC2 and MdMYB85 proteins further amplified the regulatory effect of MdMYB85 on MdMYC2 and MdAAT1, as well as that of MdMYC2 on MdMYB85 and MdAAT1. Collectively, our findings elucidate the role of the gene module consisting of MdMYC2, MdMYB85, and MdAAT1 in mediating the effects of JA and promoting ester aroma synthesis in apples.

MdERF1B-MdMYC2 module integrates ethylene and jasmonic acid to regulate the biosynthesis of anthocyanin in apple.

Ethylene and jasmonic acid (JA) are crucial hormones that promote anthocyanin synthesis in apple (Malus × domestica). However, the mechanism by which these hormones cooperate to modulate anthocyanin production in apple is unclear. According to our results, MdERF1B expression was strongly induced by ethylene and JA. Physiological phenotypes and the results of molecular biological analyses indicated that MdERF1B encodes a positive regulator of anthocyanin synthesis. Specifically, MdERF1B was capable of combining directly with the MdMYC2 promoter to promote gene expression. Additionally, MdERF1B interacted with two JA signaling pathway inhibitors, namely MdJAZ5 and MdJAZ10. The MdERF1B-MdJAZ5/10 protein complex decreased the ability of MdERF1B to activate the MdMYC2 promoter. Furthermore, MdEIL1, which is a crucial protein for ethylene signal transduction, was observed to bind directly to the MdERF1B promoter, thereby upregulating gene expression. These results suggest that MdERF1B is a core gene responsive to JA and ethylene signals. The encoded protein, together with MdMYC2, MdJAZ5/10, and MdEIL1, modulates anthocyanin synthesis in apple. This study clarifies the synergistic mechanism by which JA and ethylene regulate anthocyanin production in apple.

Transcriptome Analysis of Apples in High-Temperature Treatments Reveals a Role of MdLBD37 in the Inhibition of Anthocyanin Accumulation.

Coloring in apple fruit due to anthocyanin accumulation is inhibited by high temperature; however, the underlying mechanism remains unclear. In the present study, total anthocyanin and cyanidin 3-galactoside contents were determined and compared between cv. 'Redchief Delicious' apple fruits at 25 °C and 35 °C treatments. The high temperature (35 °C) treatment substantially decreased total anthocyanin and cyanidin 3-galactoside contents. The transcriptomes of 25 °C- and 35 °C-treated apples were analyzed by high-throughput RNA sequencing. A total of 8354 differentially expressed genes (DEGs) were detected at four time points corresponding to the two temperature treatments. The up-regulated DEGs were annotated using GO as well as KEGG databases. A network module of 528 genes (including 21 transcription factors) most associated with the total anthocyanin and cyanidin 3-galactoside contents was constructed by weighted correlation network analysis (WGCNA). In the WGCNA module, we unearthed a LOB domain-containing gene designated as MdLBD37. The expression of MdLBD37 was sharply up-regulated by high temperature and negatively correlated with the total anthocyanin and cyanidin 3-galactoside contents. Overexpression of MdLBD37 in apple fruit and calli decreased the expression of anthocyanin biosynthetic genes, such as MdCHI, MdCHS, MdF3H, MdANS, MdDFR, and MdUFGT, along with anthocyanin accumulation. Our results suggested that MdLBD37 significantly influenced the high-temperature inhibition of anthocyanin accumulation in apples. The findings shed more light on the mechanism of anthocyanin inhibition during high-temperature stress in apples.

Ethylene precisely regulates anthocyanin synthesis in apple via a module comprising MdEIL1, MdMYB1, and MdMYB17.

Ethylene regulates anthocyanin synthesis in ripening apple fruit via the antagonistic activities of the R2R3-MYB repressors and activators. However, the molecular mechanism underlying this process remains unknown. In this study, ethylene significantly induced the expression of the R2R3-MYB gene MdMYB17 in apple fruit. Moreover, MdMYB17 was revealed to be an important repressor of anthocyanin synthesis. Specifically, MdMYB17 binds directly to the promoters of the ethylene-induced genes MdMYB1 and MdEIL1, which encode positive regulators of anthocyanin synthesis, and represses their expression. Additionally, MdMYB1 and MdEIL1 bind to the MdMYB17 promoter to activate its expression. Thus, MdMYB17, MdMYB1, and MdEIL1 form a regulatory module that controls the expression of the corresponding genes. MdMYB17 interacts with MdEIL1. The interaction between MdMYB17 and MdEIL1 attenuates the regulatory effects of MdMYB17 on MdMYB1 and MdEIL1 as well as the regulatory effects of MdEIL1 on MdMYB17. Overall, our results reveal the molecular mechanisms by which MdMYB17, MdMYB1, and MdEIL1 finely mediate ethylene-regulated anthocyanin synthesis in apple fruit.