Salicylic acid accumulation causes alteration in abscisic acid signaling and induces abscisic acid insensitivity in the lesion mimic mutant cpr22

Some Arabidopsis lesion mimic mutants (LMM) show alterations in abiotic stress responses as well as pathogen resistance. cpr22 is a LMM which has a mutation in cyclic nucleotide-gated ion channels, is a typical LMM exhibiting elevated levels of salicylic acid (SA), spontaneous cell death, constitutive expression of defense genes, and enhanced resistance to various pathogens in an SA dependant manner. cpr22 defense responses are suppressed in high humidity and enhanced by low humidity. To investigate environmental effects, microarray analyses were conducted. Expression of several genes related to abscisic acid (ABA) signaling was altered and ABA levels increased in cpr22 after humidity shift. Furthermore, significant alterations in ABA-related phenotypes were observed. Double mutant analysis with nahG plants indicated that alterations in ABA signaling were attributable to elevated SA levels. These results suggest a negative effect of SA on ABA signaling/abiotic stress responses during the activation of defense responses.