Functional Characterization of in Tomato Fruit Ripening.

S-adenosylhomocysteine hydrolase (SAHH) functions as an enzyme catalyzing the reversible hydrolysis of S-adenosylhomocysteine to homocysteine and adenosine. In the present work we have investigated its role in the ripening process of tomato fruit. Among the three genes we demonstrated that was highly accumulated during fruit ripening and strongly responded to ethylene treatment. Over-expression of enhanced SAHH enzymatic activity in tomato fruit development and ripening stages and resulted in a major phenotypic change of reduced ripening time from anthesis to breaker. Consistent with this, the content of lycopene was higher in over-expression lines than in wild-type at the same developmental stage. The expression of two ethylene inducible genes ( and ) and three ethylene biosynthesis genes ( and ) increased to a higher level in over-expression lines at breaker stage, and one transgenic line even produced much more ethylene than wild-type. Although inconsistency in gene expression and ethylene production existed between the two transgenic lines, the transcriptional changes of several important ripening regulators such as and showed a consistent pattern. It was speculated that the influence of on ethylene production was downstream of the regulation of on these ripening regulator genes. The over-expressing lines displayed higher sensitivity to ethylene in both fruit and non-fruit tissues. Ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) treatment accelerated ripening faster in over-expressing fruit than in wild-type. Additionally, seedlings of transgenic lines displayed shorter hypocotyls and roots in ethylene triple response assay. In conclusion, played an important role in tomato fruit ripening.