Recognition specificity of self-incompatibility in Pyrus and Malus.

Pyrus displays gametophytic self-incompatibility controlled by a single highly polymorphic gene complex termed S locus, which comprises a stylar-expressed gene ( S-RNase) tighlty linked with a pollen expressed gene, that determines the specificity of the self-incompatibility locus. Deduced amino acid sequence of 'Meigetsu' S-RNase in Pyrus pyrifolia and 'Kuerlexiangli' S-RNase in P. sinkiangensis showed 100% identity. S-RNase in Malus spectabilis was also found to be similar to S-RNase in P. pyrifolia with 96.9% identity in the deduced amino acid sequence. The intron, which is generally highly polymorphic between alleles, was also remarkably well conserved within these allele pairs. The intron of PpS-RNase showed 95.3 and 91.9% identity with PsS-RNase and MsS-RNase, respectively. Pollen tube growth in styles, pollen tube length in artificial media containing different S-RNases and segregation of S haplotypes in F plants revealed commonality of the recognition specificity between PpS-RNase and PsS-RNase and between PpS-RNase and MsS-RNase. Results suggested that PpS-RNase, PsS-RNase and MsS-RNase have maintained the same recognition specificity after the divergence of the two species and that amino acid substitutions found between PpS-RNase and MsS-RNase do not alter the recognition specificity. [ABSTRACT FROM AUTHOR]