A novel gibberellin 2-oxidase gene CaGA2ox1 in pepper is specifically induced by incompatible plant pathogens

Abstract

Phytohormone balance is increasingly recognized as central to the outcome of plant-pathogen interactions. Differential screening for genes induced by a non-host pathogen in pepper plants (Capsicum annuum) identified a putative gibberellin 2-oxidase gene, CaGA2ox1. Analysis of the deduced amino acid sequence of CaGA2ox1 showed 53 and 50 % amino acid identity to Pisum sativum PsGA2ox2 and Arabidopsis AtGA2ox6, respectively. Expression in pepper plants of CaGA2ox1 was preferentially increased in response to non-host pathogen inoculation and during the host resistance response. CaGA2ox1 expression increased following treatment with salicylic acid and ethephon (albeit with different induction patterns), but remained unchanged following treatment with methyl jasmonate and abscisic acid. The gene product of CaGA2ox1 is predicted to catalyze the metabolism of GA(4), and does so in recombinant E. coli extracts. Further PEG-mediated transient expression studies showed that CaGA2ox1 fused with soluble modified green fluorescent protein localized to the cytosol in chili pepper protoplasts. Interestingly, the transcript level of CaGA2ox1 was not affected by treatments of either pepper with bioactive GA(4+7) or paclobutrazol, an inhibitor of GA biosynthesis. Taken together, these results provide the first evidence that a GA 2-oxidase, which is important in GA metabolism, may also play a role in plant defense signaling and plant-microbe interactions.