Transcriptome Analysis Reveals the Role of GA3 in Regulating the Asynchronism of Floral Bud Differentiation and Development in Heterodichogamous Cyclocarya paliurus (Batal.) Iljinskaja.

Cyclocarya paliurus is an important medical plant owing to the diverse bioactive compounds in its leaves. However, the heterodichogamy with female and male functions segregation within protandry (PA) or protogyny (PG) may greatly affect seed quality and its plantations for medicinal use. To speculate on the factor playing the dominant role in regulating heterodichogamy in C. paliurus, based on phenotypic observations, our study performed a multi comparison transcriptome analysis on female and male buds (PG and PA types) using RNA-seq. For the female and male bud comparisons, a total of 6753 differentially expressed genes (DEGs) were detected. In addition, functional analysis revealed that these DEGs were significantly enriched in floral development, hormone, and GA-related pathways. As the dominant hormones responsible for floral differentiation and development, gibberellins (GAs) in floral buds from PG and PA types were quantified using HPLC-MS. Among the tested GAs, GA3 positively regulated the physiological differentiation (S0) and germination (S2) of floral buds. The dynamic changes of GA3 content and floral morphological features were consistent with the expression levels of GA-related genes. Divergences of GA3 contents at S0 triggered the asynchronism of physiological differentiation between male and female buds of intramorphs (PA-M vs. PA-F and PG-F vs. PG-M). A significant difference in GA3 content enlarged this asynchronism at S2. Thus, we speculate that GA3 plays the dominant role in the formation of heterodichogamy in C. paliurus. Meanwhile, the expression patterns of GA-related DEGs, including CPS, KO, GA20ox, GA2OX, GID1, and DELLA genes, which play central roles in regulating flower development, coincided with heterodichogamous characteristics. These results support our speculations well, which should be further confirmed.