Induction of enhanced tolerance to cold stress and disease by overexpression of the pepper CaPIF1 gene in tomato

We previously isolated CaPIF1 (Capsicum annuum Pathogenesis Induced Factor) from pepper leaves following their infection with the soybean pustule pathogen Xanthomonas axonopodis pv. glycines 8ra. The CaPIF1 gene encodes a plant-specific Cys-2/His-2 zinc finger protein that functions as a transcription factor. To elucidate the role of the CaPIF1 transcription factor in gene regulation, we transformed tomato plants expressing full-length CaPIF1 and conducted microarray experiments. The ectopic overexpression of pepper CaPIF1 in tomato resulted in a massive change in gene expression: of a total of 8700 genes on the microarray, 110 were up- or downregulated, without exhibiting any visual morphological abnormality. The microarray analysis showed that CaPIF1 turned on genes involved in metabolic pathways, and stress and defense responses; the results also suggested that the upregulation of the genes might increase tolerance to cold stress and pathogen attack. The transgenic tomato displayed more tolerance to cold stress and to the bacterial pathogen Pseudomonas syringae pv. tomato DC 3000, and the tolerance levels were correlated with CaPIF1 expression levels. These results suggest that CaPIF1 is a unique Cys-2/His-2 transcription factor, regulating multiple genes both directly and indirectly, and thus conferring increased tolerance to biotic and abiotic stresses.