Bioorganic-chemical study on Self-incompatibility of Brassica

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1. The diversity of SLG (S-locus glycoprotein) in self-incompatibility of Brassica campestris was studied in terms of DNA sequences of SLGs and their related genes, SRAs. Three probes to screen SLG8 and SRA1 cDNA were snythesized based on the partial amino acid sequences of SLG8 and SRA1 proteins. Screening of a cDNA library obtained from the stigmas with the synthetic probes gave SLG8 and SRA1 cDNA clones. Using these two clones, a cDNA library of S12 homozygote was screened for SLG12 and SRA3 clones. Sequence analysis of these four clones and comparison of amino acids sequences deduced from these DNA sequences showed the presence of conserved regions of SLGs and the differences between SLGs and SRAs.2. To prove the presence of SRK (S-receptor kinase) genes in B.campestris, two primers were synthesized to correspond the conserved regions in a C-terminal part of SLG and a kinase domain. PCR with synthetic primers using first strand cDNAs obtained from mRNA of a stigmas gave anticipated PCR products encoding 800Bp fragments.3. By screening the cDNA library with the above PCR product, several clones were isolated. The cDNA sequences of SRK12 gene was deduced from the DNA sequences of these clones. It was a typical SRK gene which was composed of a SLG domain, a transmembrane domain and a kinase domain. This suggested involvement of phosphorylation in signal transduction in self-incompatibility of Brassica.4. Study on relationship between callose formation and rejection of pollen tube growth in self pollination using some inhibitors indicated that the callose formation would be the second effect of self-pollination and not the cause of inhibition of pollen tube penetration into stigmas.