Background: Pear is one of the most important fruit crops worldwide. Anthocyanins and procyanidins (PAs) are important secondary metabolites that affect the appearance and nutritive quality of pear. However, few studies have focused on the molecular mechanism underlying anthocyanin and PA accumulation in pear. Results: We conducted metabolome and transcriptome analyses to identify candidate genes involved in anthocyanin and PA accumulation in young fruits of the pear cultivar ‘Clapp Favorite’ (CF) and its red mutation cultivar ‘Red Clapp Favorite’ (RCF). Gene–metabolite correlation analyses revealed a ‘core set’ of 20 genes that were strongly correlated with 10 anthocyanin and seven PA metabolites. Of these, PcGSTF12 was confirmed to be involved in anthocyanin and PA accumulation by complementation of the tt19–7 Arabidopsis mutant. Interestingly, PcGSTF12 was found to be responsible for the accumulation of procyanidin A3, but not petunidin 3, 5-diglucoside, opposite to the function of AtGSTs in Arabidopsis. Transformation with PcGSTF12 greatly promoted or repressed genes involved in anthocyanin and PA biosynthesis, regulation, and transport. Electrophoretic mobility shift and luciferase reporter assays confirmed positive regulation of PcGSTF12 by PcMYB114. Conclusion: These findings identify a core set of genes for anthocyanin and PA accumulation in pear. Of these, PcGSTF12, was confirmed to be involved in anthocyanin and PA accumulation. Our results also identified an important anthocyanin and PA regulation node comprising two core genes, PcGSTF12 and PcMYB114. These results provide novel insights into anthocyanin and PA accumulation in pear and represent a valuable data set to guide future functional studies and pear breeding.

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.

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.

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.