Cloning and characterization of an expansin gene, RiEXP1, and a 1-aminocyclopropane-1-carboxylic acid synthase gene, RiACS1 in ripening fruit of raspberry (Rubus idaeus L.)

An alpha-expansin (RiEXPA1) gene was cloned and sequenced from raspberry. Expression of RiEXPA1 in different ripening stages of raspberry fruits has been detected. Northern blotting showed that the level of RiEXPA1 transcript accumulation increased with fruit ripening and the highest level of expression appeared at the later stages of ripening. This indicates that expression of RiEXPA1 is closely correlated with the ripening and softening of raspberry fruits. In order to determine whether expression of the RiEXPA1 was regulated by ethylene, we cloned and sequenced a 1-aminocyclo-propane-1-carboxylic acid synthase cDNA (RiACS1) that encodes the rate-limiting enzyme for ethylene production. Transcript accumulation of RiACS1 was detected at a low level only in the later stage of fruit ripening. This reveals that ethylene is not a regulatory factor of RiEXPA1 expression in raspberry fruit. The results of this investigation suggest that the expression of RiACS1 gene during ripening resembles that of non-climacteric fruits.