Identification of self-incompatibility related proteins in the pistil of Japanese pear [Pyrus pyrifolia (Burm.f.)] by proteome analysis

The differences between stylar protein of the Japanese pear (Pyrus pyrifolia (Burm.f.)) cultivars ‘Kosui’ (SS) and ‘Kikusui’ (SS) were compared by two-dimensional difference gel electrophoresis (2-D DIGE), and were labelled and visualized with different fluorescent dyes (IC3-OSu, IC5-OSu) on a single 2-D gel. The individual different expressed proteins spots were subjected to identification. The proteins were analyzed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF/MS) to identify proteins related to gametophytic self-incompatibility (GSI). S-RNase and thaumatin-like protein 1 were successfully detected as expected in the pistils of ‘Kosui’ and ‘Kikusui’. S-RNase was also detected in the pistils of ‘Kosui’. However, we could not detect S-RNase in ‘Kikusui’ in this study, possibly because the level of expression of S-RNase might be minuscule, or the estimated isoelectric point (pI) of S-RNase (pI:9.26) was more basic than S-RNase (pI: 9.17) and S-RNase (pI: 9.01). These results indicate that proteomic studies are effective tools for detection of the expected proteins and might be helpful for finding the unknown key proteins related to the mechanism of self-incompatibility (SI) in many other SI plants.