Poster: Cell Walls

Abs # 1257: Divergent expression of six expansin genes during apple fruit ontogeny

Presenter:	Harada, Takeo , tharada@cc.hirosaki-u.ac.jp
Authors	Harada, Takeo  (A)   Wakasa, Yuhya  (A)   Hatuyama, Yoshimichi  (B)   Sato, Takashi  (C)
Affiliations:	(A): Hirosaki University (B): Aomori GreenBio Center (C): Aomori Apple Experiment Station

Expansins are cell wall elooseningf proteins which are proposed to function slippage between the cell wall network of cellulose microfibrils and adhering polysaccharide. The occurrence of multigene families of expansins have been identified from many plant species, and their expression profiles suggest that different expansins play unique developmental or tissue-specific roles. Expansin genes were also expressed in the developing fruits and ripening fruits such as tomato. However, there was no report of apple fruit so far. We report the expression characteristics of six apple (Malus~domestica Borkh.) expansin genes, MdExp1 isolated as a cDNA from cultured shoot, MdExp2-4 from the flesh of ripening fruit, and MdExp5 and 6 from fruit pedicel tissue including the abscission zone. RNA gel blot analysis of these cDNAs during fruit development revealed a unique pattern of expression for each cDNA. Exp1 was expressed up-down-up cycles throughout from full-bloom stage to just before ripening. Exp2 and Exp5 initiated the expressions when cell expanding growth was started after cell proliferation growth stage. Transcripts of Exp3 and Exp4 were detected in all stage, but Exp3 was strongly expressed at the ripening stage. Exp6 was not expressed any growth stage, but induced by wounding. These results suggest that apple fruit requires at least six expansin genes during ontogeny and Exp3 is ripening-related expansin gene.