Elucidation of ethylene signal transduction mechanism and its regulation on fruit maturation, ripening and occurrence of physiological disorder

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This study was carried out to elucidate of ethylene signal transduction mechanism and its regulation on fruit maturation, ripening and rapid softening as a physiological disorder after deastringency, using several cultivars of persimmon. Irrespective of cultivars, it is clear that ethylene promotes the softening because 1-MCP treatment depressed the cell wall degradation enzymes activities and their encoding genes such as β-galactosidase (DKB-gal) and xyloglucan endotransglycosylase (DKXTH1). Similarly, DKXTH1 was induced by alcohol treatment on 'Saijo' young fruit. On the contrary, it was found on 'Saijo' after deastringency treatment that xylosidase/afrbinofranosidase genes (DKARF1 and 2) expression was promoted.Expression of ethylene biosynthesis enzymes genes were analyzed throughout the fruit development and maturation of both cultivars ; 'Saijo' and 'Rendaiji', As a result, there were difference in strongly expressed genes between young and ripened fruits ; DKACS2 and DKACS3 as A … More CC synthesis enzyme genes were prominent in young 'Saijo' and 'Rendaiji' fruits, respectively. By contrast in ripened fruit, DKACS1 was supposed to be a major gene to function in parallel with DKACO1 and DKACO2 expression as ACC oxidation enzyme genes in both cultivars.Three full-length persimmon cDNAs homologous to Arabidopsis ethylene receptor genes ERS1, ETR1, and ETR2 were isolated. Subsequently, DkERS1, DkETR1, and DkETR2 were designated, respectively, and examined their expression during fruit development and ripening. DkETR1 mRNA expression remained at a basal level throughout all stages examined and was not affected by ethylene treatment. In contrast, expression of DkERS1 and DkETR2 mRNAs was correlated with ethylene production during fruit development and ripening and was enhanced after ethylene treatment. Western blot analysis using anti-DkERS1 antibody showed that expression of DkERS1 protein degreased gradually towards maturation and reached the lowest level at the ripening stage, in agreement with the ethylene receptor-inhibition model. These results imply that DkERS1 may play a major role in sensing ethylene signals associated with fruit development and ripening. Less