Poster: Cell walls

Abs # 607: Biochemical property and in vivo function of rice β-expansins

Presenter:	Choi, Dongsu , choid@msu.edu
Authors	Choi, Dongsu  (A)   Lee, Yi  (A) (B)  Kende, Hans  (A)
Affiliations:	(A): Michigan State University (B): Chungbuk National University

α-expansins are bound to the cell wall of plants and can be solubilized with an extraction buffer containing 1 M NaCl. Localization of α-expansins in the cell wall was confirmed by immunogold labeling and electron microscopy. The subcellular localization of vegetative β-expansins has not yet been studied. Using antibodies raised against OsEXPB3, a vegetative β-expansin of rice (Oryza sativa L.), we found that OsEXPB3 is tightly bound to the cell wall and, unlike α-expansins, cannot be solubilized with extraction buffer containing 1 M NaCl. OsEXPB3 protein could only be extracted with buffer containing SDS. The subcellular localization of the OsEXPB3 protein was confirmed by immunogold labeling and electron microscopy. Gold particles were mainly distributed over the primary cell walls. Immunohistochemistry showed that OsEXPB3 was present in all regions of the coleoptile and root tissues tested. To investigate the in vivo function of β-expansins, we generated transgenic rice plants carrying sense OsEXPB3 cDNA constructs. In germination experiments using control transgenic T1 seeds and sense transgenic T1 seeds, we observed enhanced coleoptile growth and root growth by up to 35.6% and 29%, respectively. Interestingly, OsEXPB3 transgenic seedlings did not show any change in mesocotyl growth, while regulated expression of OsEXP4 greatly affected mesocotyl growth in transgenic seedlings. This result suggests that β-expansins also act as a primary wall-loosening factors in rice cell walls but that they may have different organ specificities than do α-expansins.