JAZ1-3 and MYC2-1 Synergistically Regulate the Transformation from Completely Mixed Flower Buds to Female Flower Buds in Castanea mollisima

Chestnut (Castanea mollisima) is an important woody food crop, but its yield has been low in cultivation, mainly due to the problems of fewer female flowers and more male flowers. Therefore, regulating the transition of chestnut flowers and effectively balancing the proportion of male and female to improve the yield are key factor to be solved in production. In this study, the chestnut floral buds in pre- and post-winter were used as materials. The data of metabolites, hormones, and gene expression during flower bud differentiation of chestnut were analyzed by transcriptomics and metabolomics to preliminarily reveal the possible reason of male and female flower bud transformation in pre- and post-winter. The analysis of Differentially Expressed Genes (DEGs) showed that there were 6323 DEGs in the Complete mixed flower bud (CMF) group in pre- and post-winter, of which 3448 genes were up-regulated and 2875 genes were down-regulated. There were 8037 DEGs in the Incomplete mixed flower bud (IMF) in pre- and post-winter, of which 4546 genes were up-regulated and 3491 genes were down-regulated. A total of 726 genes from the two flower buds were enriched into 251 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways in post winter, of which plant hormone signal transduction accounted for 4.13%. The analysis results of differential metabolites showed that the differential metabolites of the two flower buds were mainly concentrated in the secondary metabolic synthesis pathway. The difference of hormone content showed that the content of Gibberellin 9 (GA9) and GA19 in CMF was higher than that in IMF in pre-winter, but the opposite in post-winter. Methyl jasmonate (MeJA) content was only very high in CMF in pre-winter, while Jasmonoyl-(l)-Isoleucine (JA-ILE) showed high content in CMF in post-winter. In post-winter, higher concentration of JA-ILE was positively correlated with the expression of Flowering Locus T (CmFT), and CmFT gene was significantly positively correlated with the expression levels of MYC2-1, MYC2-2 and LFY 3 (LEAFY 3). The higher concentration of JA-ILE was negatively correlated with the transcription level of JAZ1-3. In vitro experiments further verified that Jasmonate-Zim 1-3 (JAZ 1-3) combined with MYC2-1 inhibited the transcription of CmFT gene, while MYC2-1 alone promoted the expression of FT. The results suggested that a higher concentration of GA is conducive to breaking the dormancy of flower buds and promoting the development of male flower buds, while a lower concentration of GA and a higher concentration of JA-ILE are conducive to the differentiation and formation of female flower buds in post-winter, in which JAZ1-3 and MYC2-1 play a key role in the differentiation of female flower buds of chestnut.