Two tomato cDNA clones with homology to the 14-3-3 family of proteins were identified through immunoscreening a ripening tomato fruit library (Clontech). These two clones share approx. 71% identity at the nucleotide level and 84% identity at the deduced amino acid level, with radical amino acid substitutions clustering at the acidic carboxy-terminus. Southern hybridization data indicate that each clone represents a unique gene. Distinct transcript accumulation patterns during tomato fruit ripening together with the homology to brain regulatory proteins suggest potential involvement in fruit development.

Fusicoccin (FC) is a fungal toxin that activates the plant plasma membrane H+-ATPase by binding with 14-3-3 proteins, causing membrane hyperpolarization. Here we report on the effect of FC on a gene-for-gene pathogen-resistance response and show that FC application induces the expression of several genes involved in plant responses to pathogens. Ten members of the FC-binding 14-3-3 protein gene family were isolated from tomato (Lycopersicon esculentum) to characterize their role in defense responses. Sequence analysis is suggestive of common biochemical functions for these tomato 14-3-3 proteins, but their genes showed different expression patterns in leaves after challenges. Different specific subsets of 14-3-3 genes were induced after treatment with FC and during a gene-for-gene resistance response. Possible roles for the H+-ATPase and 14-3-3 proteins in responses to pathogens are discussed.