Phytohormone requirements for pollination drop secretion in Ginkgo biloba ovules

Abstract

Pollination drop (PD) plays a crucial role in the sexual reproduction of gymnosperms. However, the molecular mechanism regulating PD secretion has not been reported. In our study, we successfully constructed cDNA libraries in ovules between PD secretion and PD withdrawal stages, and identified 2975 differentially expressed genes (DEGs). These genes were involved in biosynthesis of secondary metabolites, fatty acid biosynthesis, fatty acid metabolism, and hormone-related pathways. We especially identified DEGs related to jasmonic acid (JA) metabolism and signal transduction, including Gb_39942 (SDP1), Gb_03931 (OPR2), and Gb_18696 (4CLL4), which were all upregulated at the stage of PD secretion in Ginkgo biloba L. Gb_17431 (TIF3B) and Gb_17432 (TIF9), which encode the negative regulator JAZ protein, were downregulated during this period. We also found that KO1 (Gb_05787 and Gb_38576) and GA20ox1 (Gb_16591), which are related to gibberellin (GA) synthesis, were upregulated, whereas Gb_17754, encoding the GA receptor GID1, was downregulated during PD secretion. From these results, we predicted that JA and GA may play important roles in the regulation of PD secretion in G. biloba ovules.