Molecular analysis of two Chinese pear (Pyrus bretschneideri Rehd.) spontaneous self-compatible mutants, Yan Zhuang and Jin Zhui

Yan Zhuang and Jin Zhui are spontaneous bud mutants of Chinese pear (Pyrus bretschneideri Rehd.) from Ya Li. Both fruit set rate and seed number after self-pollination, together with pollen tube growth, prove that Yan Zhuang and Jin Zhui are self-compatible. The fruit set rate and seed number after cross-pollination suggest that the self-compatibility of Yan Zhuang and Jin Zhui may be due to natural mutations of the stylar S allele and pollen S allele, respectively. PCR amplification of the S-RNase gene in self-pollinated progeny of Yan Zhuang and Jin Zhui show that they contain point mutations in the stylar S-21 allele and pollen S-34 allele, respectively. The cDNA sequence of the Yan Zhuang stylar S-RNase gene revealed that the 182nd nucleotide of the S-21-RNase (cDNA) sequence had been substituted resulting in a Gly to Val mutation, and this might affect the stability of the S-RNase. In addition, Western blotting showed that one Yan Zhuang stylar S-RNase was absent and the expression level of another S-RNase protein was decreased compared to Ya Li. Therefore, we suggest that the self-compatibility of Yan Zhuang is caused by a point mutation in an S-21-RNase nucleotide.