A gene coding for tomato fruit beta-galactosidase II is expressed during fruit ripening. Cloning, characterization, and expression pattern

摘要

A cDNA for beta-galactosidase (EC 3.2.1.23) II, pTombetagal 4 (GenBank accession no. AF020390), was cloned and its gene expression during fruit ripening was studied. Northern-blot analysis showed that the beta-galactosidase II gene transcript was detectable at the breaker stage of ripeness, maximum at the turning stage, and present at decreasing levels during the later stages of normal tomato fruit ripening. At the turning stage of ripeness, the transcript was present in all fruit tissues and was highest in the outermost tissues (including the peel). Confirmation that pTombetagal 4 codes for beta-galactosidase II was derived from matching protein and deduced amino acid sequences. Furthermore, analysis of the deduced amino acid sequence of pTombetagal 4 suggested a high probability for secretion based on the presence of a hydrophobic leader sequence, a leader-sequence cleavage site, and three possible N-glycosylation sites. The predicted molecular mass and isoelectric point of the pTombetagal 4-encoded mature protein were similar to those reported for the purified beta-galactosidase II protein from tomato fruit.