Ethylene regulation of fruit softening and cell wall disassembly in Charentais melon

Kiyomi Nishiyama , Monique Guis (1) , Jocelyn K. C. Rose , Yasutaka Kubo , Kristen A. Bennett , Lu Wangjin , Kenji Kato , Koichiro Ushijima , Ryohei Nakano , Akitsugu Inaba , Mondher Bouzayen (1) , Alain Latché (1) , Jean-Claude Pech (1) , Alan B. Bennett

1 GBF - Génomique et Biotechnologie des Fruits

Cell wall disassembly in ripening fruit is highly complex, involving the dismantling of multiple polysaccharide networks by diverse families of wall-modifying proteins. While it has been reported in several species that multiple members of each such family are expressed in the same fruit tissue, it is not clear whether this reflects functional redundancy, with protein isozymes from a single enzyme class performing similar roles and contributing equally to wall degradation, or whether they have discrete functions, with some isoforms playing a predominant role. Experiments reported here sought to distinguish between cell wall-related processes in ripening melon that were softening-associated and softening-independent. Cell wall polysaccharide depolymerization and the expression of wall metabolism-related genes were examined in transgenic melon (Cucumis melo var. cantalupensis Naud.) fruit with suppressed expression of the 1-aminocyclopropane-1-carboxylate oxidase (ACO) gene and fruits treated with ethylene and 1-methylcyclopropene (1-MCP). Softening was completely inhibited in the transgenic fruit but was restored by treatment with exogenous ethylene. Moreover, post-harvest application of 1-MCP after the onset of ripening completely halted subsequent softening, suggesting that melon fruit softening is ethylene-dependent. Size exclusion chromatography of cell wall polysaccharides, from the transgenic fruits, with or without exogenous ethylene, indicated that the depolymerization of both pectins and xyloglucans was also ethylene dependent. However, northern analyses of a diverse range of cell wallrelated genes, including those for polygalacturonases, xyloglucan endotransglucosylase/hydrolases, expansin, and b-galactosidases, identified specific genes within single families that could be categorized as ethylene-dependent, ethylene-independent, or partially ethylene-dependent. These results support the hypothesis that while individual cell wall-modifying proteins from each family contribute to cell wall disassembly that accompanies fruit softening, other closely related family members are regulated in an ethylene-independent manner and apparently do not directly participate in fruit softening.

Mots clés: Cell wall modification; Enzyme; Fruit softening; Gene expression; 1-MCP; Melon fruit; Transgenic plant

Domaines: Biologie végétale; Agronomie; Biotechnologies

Kiyomi Nishiyama, Monique Guis, Jocelyn K. C. Rose, Yasutaka Kubo, Kristen A. Bennett, et al.. Ethylene regulation of fruit softening and cell wall disassembly in Charentais melon. Journal of Experimental Botany, 2007, 5 (6), pp.1281-1290. ⟨10.1093/jxb/erl283⟩. ⟨hal-03594407⟩