Regulation of gene expression by ethylene during Lycopersicon esculentum (tomato) fruit development.

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Abstract
We have investigated the regulation of gene expression by the plant hormone ethylene by cloning mRNAs that accumulate in unripe tomato fruit (Lycopersicon esculentum) exposed to exogenous ethylene. The response to exogenous ethylene is rapid; within 30-120 min we detect an increase in the cloned mRNA concentrations. DNA sequence analysis indicates that one of the ethylene-inducible genes is related to a gene encoding wound-inducible proteinase inhibitor I. We have measured ethylene production during fruit development and detect low basal levels in unripe fruit and much higher levels in ripening fruit. Both hybridization experiments show that expression of the cloned genes is developmentally regulated by ethylene during fruit ripening: the mRNAs produced by these genes are more abundant in ripe fruit than in unripe fruit, and this mRNA accumulation is repressed by a competitive inhibitor of ethylene action, norbornadiene. However, during fruit development some of the cloned mRNAs begin to accumulate when ethylene production is a basal level, whereas other mRNAs begin to accumulate later when the endogenous ethylene concentration increases, suggesting that gene expression during fruit development can be activated by ethylene in two ways. In some cases gene expression is primarily activated by an increase in sensitivity to basal ethylene levels, whereas in other cases it may be regulated by an increase in ethylene concentration.