Poster: Reproductive development

Abs # 360: KOMPEITO is important for callose accumulation and the exine pattern formation in Arabidopsis.

Presenter:	Kanaoka, Masahiro , mkanaoka@ok-lab.bot.kyoto-u.ac.jp
Authors	Kanaoka, Masahiro  (A)   Kentaro, Shimizu K (A) (B)  Kiyotaka, Okada  (A)
Affiliations:	(A): Department of Botany, Graduate School of Science, Kyoto University (B): Department of Genetics, North Carolina State University

The first step of cell-cell interaction between male and female reproductive organs is the pollen-stigma adhesion, in which pollen grains are physically attached to the stigma. It is suggested that the morphology of the outermost layer of pollen grains, the exine layer, is important for this adhesion event. The exine layer is formed during tetrad stage when microspores are surrounded by primexine matrix and callose wall. Sporopollenin is deposited onto the plasma membrane of microspores and then surrounded by primexine matrix. Therefore, the regulation of these wall materials is important for precise formation of the exine layer. However, little is known about the molecular mechanism of the generation of the pollen wall. kompeito (kom) is defective in the surface sculpture of the pollen grains and pollen-stigma adhesion, resulting in reduced fertility. The defect in kom was first observed during meiosis stage. In kom, callose wall was not found around the pollen mother cell. In tetrad stage, the amount of callose and primexine matrix was much smaller than wild type. At the same stage, sporopollenin was randomly deposited onto the plasma membrane of the microspore, and following formation of the exine layer was disrupted. KOM gene was isolated by map-based cloning and found to encode a seven-path transmembrane protein. KOM was specifically expressed in pollen mother cells during meiosis stage. KOM-GFP fusion protein was detected as small dots in the cytoplasm, and the signals were merged with RGP1, a Golgi marker. Furthermore, by BFA treatment, the dot signals disappeared. These results suggest that KOM is localized in Golgi apparatus. A possible role of KOM and other genes that may be related to exine formation and callose accumulation will be discussed.