Comparative transcriptome analysis reveals the late-acting self-incompatibility and identification of RNase T2 family members in Camellia oleifera

Background:The Camellia oil tree(Camellia oleifera Abel.)is an important nonwood forest species in southern China,and most Camellia oil tree cultivars are late-acting self-incompatibility(LSI)types.Although several studies examined the mechanism of LSI,the process is quite complicated and unclear. Result:The present study investigated pollen tube growth and fruit setting of two Camellia oil tree cultivars Huashuo(HS)and Huajin(HJ)after non-and self-pollination,and transcriptomic analysis of the ovaries was performed 48 h after self-pollination to identify the candidate genes involved in the LSI of Camellia oil tree.The results showed that the fruit set of HS after self-pollination was significantly higher than that of HJ.Transcriptomic analysis revealed that plant hormone signal transduction,ATP-binding cassette(ABC)transporters,the phosphatidylinositol signaling system,reactive oxygen species(ROS)metabolism,and Ca2+ signaling were mainly involved in the LSI of Camellia oil tree.Moreover,nine RNase T2 genes were identified from the transcriptome analysis,which also showed that CoRNase7 participated in the self-incompatibility reaction in HS.Based on phylogenetic analysis,Co RNase6 was closely related to S-RNase from coffee,and Co RNase7 and Co RNase8 were closely related to S-RNase from Camellia sinensis.The 9 RNase T2 genes successfully produced proteins in prokaryotes.Subcellular localization indicated that CoRNase1 and CoRNase5 were cytoplasmic proteins,while Co RNase7 was a plasma membrane protein. Conclusions:These results preliminarily revealed the molecular mechanism of LSI in Camellia oil tree,and SI signal transduction might be regulated by a large molecular regulatory network.The discovery of T2 RNases provided evidence that Camellia oil tree might be under RNase-based gametophytic self-incompatibility.