Inhibition of the Plastidic ATP/ADP Transporter Protein Primes Potato Tubers for Augmented Elicitation of Defense Responses and Enhances Their Resistance against Erwinia carotovora

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Abstract
Tubers of transgenic potato (Solanum tuberosum) plants with decreased activity of the plastidic ATP/ADP transporter AATP1 display reduced levels of starch, modified tuber morphology, and altered concentrations of primary metabolites. Here, we demonstrate that the spontaneous production of hydrogen peroxide, the endogenous content of salicylic acid, and the levels of mRNAs of various defense-related genes are similar in tuber discs of wild-type and AATP1(St) antisense plants. However, upon challenging the tissue with fungal elicitors or culture supernatants of the soft rot-causing pathogen Erwinia carotovora subsp. atroseptica, the AATP1(St) antisense tubers exhibit highly potentiated activation of defense responses when compared with wild-type tissue. The augmented defense responses comprise enhanced accumulation of transcripts of five defense-related genes (beta-1,3-GLUCANASE B2 and A1, CHITINASE B3 and A2, and Phe AMMONIA-LYASE) and enhanced elicitation (up to 21-fold) of the early hydrogen peroxide burst. The potentiated activation of cellular defense responses in AATP1(St) antisense tubers is not accompanied by a precedent increase in endogenous salicylic acid levels, but is associated with a strongly enhanced resistance of the tissue to E. carotovora. From these results, we conclude that inhibition of primary metabolic reactions induces a primed state that sensitizes the potato tubers for improved elicitation of various cellular defense responses, which likely contribute to enhanced E. carotovora resistance.