Two MdERFs (ethylene-response factors) were isolated from ripening apple (Malusxdomestica Borkh. cv. Golden Delicious) fruit. The features of their conserved motifs indicated that MdERF1 and MdERF2 belong to group VII and group IX categories in Arabidopsis, respectively. MdERF1 was expressed predominantly in ripening fruit, although a small degree of expression was also observed in non-fruit tissues, whereas MdERF2 was expressed exclusively in ripening fruit. The increased expression in ripening fruit was repressed by treatment with 1-methylcyclopropene (1-MCP: a potent antagonist of ethylene receptors), indicating that transcription is regulated positively by the ethylene signalling system. Indeed, it was a tendency for cultivars with low ethylene production to show lower MdERFs expression than those with high ethylene production. On the basis of concomitant analyses of the expression of some genes related to ripening, the functions of MdERFs and the role of ethylene in the ripening process are discussed.
Four S-RNases (RNase associated with self-incompatibility) were purified from the styles of two apple cultivars (Malus domestica), a self-incompatible cv., Starking Delicious (SD), and a self-compatible cv., Megumi (MG). Each cultivar produced two S-RNases and their enzymatic properties such as specific activity, pH optimum, thermal stability, and molecular mass, were characterized. The four S-RNases inhibited the tube growth of apple pollen in an in vitro bioassay at 25 microg/ml (1.0 microM), but did not distinguish self from non-self pollen. The cDNAs of four S-RNases were cloned, and the nucleotide and deduced amino acid sequences were analyzed. The nucleotide sequence of SD-Se RNase was a new one and the other was identical to that of Sc-RNase of cv. Fuji. In MG one was identical to the sequence of SD-Sc RNase and the other to that of Sa-RNase of cv. Golden Delicious except for one base. From results of the isolation amounts and the Western blot analysis for stylar crude extracts the amount of S-RNases in MG was apparently less than that in SD.
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