Transcription Factor and Zeatin Co-Regulate Mixed Catkin Differentiation of Chinese Chestnut (Castanea mollissima)

Abstract

Castanea mollissima is an important monoecious fruit crop with high economic and ecological value in China. However, its yield is restricted by an imbalanced ratio of male and female flowers for chestnut production. To address this issue, we examined the morphology of bisexual flower organs, measured the levels of endogenous hormones in the flowers, profiled gene expression related to plant hormone biosynthesis and signaling pathways and transcription factors, and investigated the effects of exogenous jasmonic acid (JA) and zeatin (ZT) hormone application on flower development in C. mollissima ‘Tanqiao’. Morphological studies indicated that the development of male and female flowers can be divided into nine and eight stages, respectively. Male flowers contained higher levels of gibberellic acid (GA3) and abscisic acid (ABA) than female flowers, whereas female flowers had higher levels of JA and ZT. The analysis of the Kyoto encyclopedia of genes and genomes (KEGG) pathways revealed that the major significant enrichment pathways of differentially expressed genes (DEGs) consisted of plant hormone signal transduction and zeatin biosynthesis. Through time-series analyses, we screened 3 genes related to jasmonic acid biosynthesis and signal transduction and 21 genes related to zeatin biosynthesis and transduction. Among these genes, only the gene family LOG, related to zeatin biosynthesis, was highly expressed in female flowers. This result indicated that LOG may be the core gene hormone family involved in regulating female flower development. However, a weighted gene co-expression network analysis (WGCNA) suggested that IDD7 was the core gene involved in regulating female flower development. The results of exogenous hormone application indicated that zeatin could greatly increase the quantity of fertile female flowers, but JA was not significant. These findings demonstrated that zeatin and transcription factors were crucial regulators in the formation of female flowers in C. mollissima.