Secretion of the 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 are all upregulated at the stage of PD secretion in Ginkgo biloba. Gb_17431 (TIF3B) and Gb_17432 (TIF9), which encode the negative regulator JAZ protein, are 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, had increased expression, whereas Gb_17754, encoding the GA receptor GID1, is downregulated at the 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.
The behavior of pollination drop secretion in Ginkgo biloba L.
