Differential regulation of four members of the ACC synthase gene family in plum

The regulation of ACC synthase ( ACS) genes was studied in early ('Early Golden') and late ('Shiro') Japanese plum cultivars ( Prunus salicina L.) in order to determine the role of this gene family in fruit ripening. Of the four Ps-ACS cDNAs isolated, two ( PsACS1 and - 3) showed differential expression between the two cultivars. Ps-ACS1 accumulated during fruit ripening of ` Early Golden' ('EG') and ` 'Shiro' ('SH') in ethylene-dependent and - independent manners, respectively. Ps-ACS3a transcripts accumulated throughout fruit development and during 'EG' fruit ripening. Ps-ACS3b was detected only during ripening of 'SH' fruit. Furthermore, Ps-ACS3a transcript accumulation was negatively regulated by ethylene, whereas Ps-ACS3b was positively induced by the hormone. In both cultivars, the expression of Ps-ACS4 and - 5 is under positive and negative feedback control by ethylene, respectively. Genetic analyses of 'EG' and 'SH' cultivars demonstrated that 'EG' is homozygous for Ps-ACS3a whereas 'SH' is heterozygous for Ps-ACS3 (a/b). The role of ethylene-overproducer 1-like in delaying fruit ripening by interacting with Ps-ACS proteins was also studied. The effect of the plant hormones, auxin, gibberellin, and cytokinin, in regulating ethylene production by promoting the induction of the different Ps-ACS mRNAs in plum was investigated. A model is presented in which differences in Ps-ACS alleles and gene expression between early and late plums are critical in determining the ripening behaviour of the cultivars.