Molecular Genetic Analysis Of Self-compatible ‘jin Zhui’ And Functional Study Of The Pollen S Genes MdSFBB9α And MdSFBB9β

In many flowering plants, Self-incompatibility (SI) is a genetic mechanism that prevents self-fertilization and promotes cross-fertilization. In Solanaceae, Plantaginaceae and Rosaceae, SI is controlled by a single multi-allelic S locus, which is comprised of pistil-S gene and pollen-S gene. The pistil-S gene encodes a polymorphic ribonuclease (S-RNase), and the pollen-S gene is comprised of a cluster of pollen-expressed S-locus F-box genes named SLF/SFBB in different species. In Solanaceae and Rosaceae, the pollen S genes were recently proposed to involve in a’non-self recognition by multiple factors’ system. In this study,’Jin Zhui’, a self-compatible spontaneous mutant of ’Ya Li’ was studied. The results suggest that mutant non-S factor is responsible for self-compatible ’Jin Zhui’. And meanwhile, the similarity of self-incompatible system was studied by transgenic method between Solanaceae and Rosaceae.The main results of this study are as follows:1. To investigate the pollen part mutant ’Jin Zhui’,5SFBB genes which located in S-locus, were indentified from ’Ya Li’(Pyrus bretschneideri Rhed.). Genetic linkage analysis revealed that they belong to the pollen S gene. No nucleotide differences were found in the SLF genes of ’Jin Zhui’. Further genetic analysis suggested that non-S factor mutation is responsible for the change from self-incompatibility to self-compatibility. These findings support the hypothesis that loss of function of S-locus unlinked PPM expressed in pollen leads to SI breakdown in ’Jin Zhui’. Secondly, abnormal meiosis was observed in quite a few ’Jin Zhui’ pollen mother cells (PMCs), while not found in ’Ya Li’. These and other interesting findings are discussed.2. To investigate the function of two SFBB alleles, MdSFBB9a and MdSFBB9β, which are tightly linked to S-RNase, were isolated from ’Fuji’(Malus pumila.cv.’Fuji’), and were transferred into Petunia hybrida (S3S3L). The results indicated the breakdown of self-incompatibility was only observed in MdSFBB9β transgenic P. hybrida (S3S3L), which indicates that the apple MdSFBB9β may play the role of pollen S factor in P. hybrida, and also imply its pollen S factor role in’Fuji’, It was the first time to find the self-incompatibility breakdown between the Solanaceae and Rosaceae, and is also consistent with the idea that the two families exhibit the same type’non-self recognition by multiple factors’in self-incompatibility mechanism. However no homozygote was found in the progeny. These interesting findings are discussed.Taken together, it is the first time that we find the breakdown of self-incompatibility in Maloideae was due to S-locus unlinked PPM. The identification of S-locus unlinked PPM in Pyrus give a more complete picture of the self-incompatible mechanism. The transgenic results between Solanaceae and Rosaceae support MdSFBB9β was a pollen S and that the two families exhibit the same type ’non-self recognition by multiple factors’ in self-incompatibility mechanism.