A Low Transcriptional Level of Se-RNase in the Se -haplotype Confers Self-compatibility in Japanese Plum

Abstract

Most commercial cultivars of japanese plum ( Prunus salicina Lindl.) exhibit S-RNase-based gametophytic self-incompatibility (GSI), although some self-compatible (SC) cultivars exist. In this study, we characterized S-RNase and SFB , the pistil and pollen S determinants of the specificity of the GSI reaction, respectively, from four S -haplotypes, including a SC ( S e ) and three SI ( S a , S b , and S c ) S -haplotypes of japanese plum. The genomic organization and structure of the SC S e - haplotype appear intact, because the relative transcriptional orientation of its S-RNase and SFB and their intergenetic distance are similar to those of the other three SI S -haplotypes of japanese plum and other Prunus L. species. Furthermore, there is no apparent defect in the DNA sequences of S e -RNase and SFB e . However, a series of transcriptional analyses, including real-time reverse transcriptase–polymerase chain reaction, showed that the S e -RNase transcript levels in the pistil are significantly lower than those of the S a - , S b - , and S c -RNase s, although transcripts of SFB a , SFB b , SFB c , and SFB e are present at similar levels in pollen. Furthermore, no S e -RNase spot was detected in two-dimensional polyacrylamide gel electrophoresis profiles of stylar extracts of the cultivars with the S e - haplotype. We discuss the possible molecular basis of SC observed with the S e -haplotype with special reference to the insufficient S e -RNase accumulation incited by the very low transcriptional level of S e -RNase in pistils.