Identification and analysis of CdS-RNase in Camellia drupifera: A key determinant of late-acting self-incompatibility

Abstract

Plant self-incompatibility (SI) is of great significance in reproductive biology and is also the main factor affecting yield in agricultural production. Late-acting self-incompatibility (LSI) is one of the main types of plant SI, but the mechanism of LSI is not systematically analyzed. Tea oil Camellia, a strictly outcrossing plant, is a well-known woody oil cash crop. SI is one of the main reasons for the low yield of tea oil Camellia. In this study, we found that C. drupifera, one of the main species of tea oil Camellia, shows LSI, in which SI occurs in the style, and pollen tube growth in the ovary ceases at 96 h after selfing. The CdS-RNase gene of Camellia drupifera was successfully cloned, and the gene showed a length of 922 bp and encoded 238 amino acids. CdS-RNase had typical S-RNase characteristics. The functional validation results revealed that CdS-RNase was a key female factor for SI in C. drupifera, indicating that S-RNase plays an important role in the plant LSI mechanism. CdS-RNase localized to the cell membrane, was specifically expressed in the style and transferred to the ovary, and inhibited pollen tube growth in the style and ovary. There was an "enhancer factor" for the expression of CdS-RNase in selfing styles. Between 24 h and 48 h after selfing, CdS-RNase expression was significantly upregulated 28.3 times, which was more than 2.5 times higher than the outcross expression level and more than 5 times lower than the cross expression level. A total of 28 CdS-RNase proteins were identified, including 6 CdSm-RNases, and outcrossing among different CdS-RNase genotypes had a significant effect on the fruit setting rate. It may be that mismatches among CdS-RNase genotypes and self-inbreeding are the main reasons for the low yield of C. drupifera. These results provide a basis for the systematic analysis of the LSI mechanism and for solving the SI problem of tea oil Camellia.