Identification of key factor fur cell wall disassembly in fruit by proteome analysis and transgenic technology

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Cell wall is main factor for physical structure of plant and the main limiting factors limiting their storage, transport and marketability. Previous studies indicated importance of plant hormone ethylene for fruit ripening and softening. However, key factor (s) in cell wall disassembly have not been identified. 'La France' European pear fruit and melon fruit undergo dramatic softening during ripening in an ethylene-dependent manner, whereas Chinese pear does not exhibit softening in spite of its massive ethylene production during ripening. To broad-scale and comprehensive screening for factors involved in fruit softening, in addition to gene expression analysis of polygalacturonase, α-arabinofuranosidase and β-galactosidase, the two-dimensional gel electrophoresis profiles and YSST analysis of cell wall proteins were employed. The accumulation levels of 200 protein spots were isolated in the ripening 'La France' pear. When softening pears of this variety were treated with 1-MCP, a strong ethylene inhibitor, fruit softening was retarded. On the comparison between treated and non-treated fruit, 3 protein spots were selected as candidates for key factors of fruit softening, since their accumulation showed specific pattern for softening.On YSST analysis, 170 clones (70 contigs and 100 singletons) encoding secreted proteins including clones which have not been previously reported were isolated. Based on the macroarray analysis, 28 clones showed elevated or down-regulated expression with pear fruit development and ripening. On comparison in 'La France' and the non-softening 'Yali' pear fruit, 11 potential new cell wall modifying proteins among 28 clones were selected for candidates for key factor of fruit softening.