| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2002: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2001: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2000: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
Self-incompatibility is a system by which pistil can recognize self and nonself pollen and can be fertilized with only nonself-pollen. The purposes of this project are to identify pistil and pollen factors responsible for gametophytic self-incompatibility (GSI), and to clarify its molecular mechanism. During the last three years, 2000-2002, we determined the three dimensional structure of S3-RNase of Pyrus pyrifolia, a member of Rosaceae, at 1.5 A resolution by X-ray crystal analysis, showing the putative recognition sites on the S-RNase to a pollen factor. Recently, an F-box gene, expressed in a pollen-specific manner, has been found within S-locus and is strongly suggested to be a pollen factor. However, neither the interaction between the F-box protein and the S-RNase nor the participation of ubiquitin-proteasome system in GSI has been directly demonstrated. Therefore, we have constructed in vitro system of pollen tube growth inhibition by hanging drop method using purified S-RNase. Next, using this system, we analyzed proteins expressed specifically on pollen tube inhibition and checked the structural changing of the S-RNase. As a result, the 13 proteins expressed specifically were detected but the F-box protein was not included in these proteins. It is interesting that the S-RNase invaded into the pollen tube is susceptive to some post-translational modifications and is separated into several spots on a 2D-PAGE gel. After 12 hrs from when the S-RNase was taken into the pollen tube, it was completely degraded, which has never been observed using RNase T2 or RNase A. These results suggest that some systems located in the pollen tube may positively modify and degrade the invading S-RNase.
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