Genetic requirements for infection-specific responses in conferring disease resistance in Arabidopsis

YOO, SUNG-JE; CHOI, HYO JU; NOH, SEONG WOO; CECCHINI, NICOLÁS M.; GREENBERG, JEAN T.; JUNG, HO WON

Frontiers in Plant Science

Frontiers

Año: 2022 vol. 13

Immunity in plants arises from defense regulatory circuits that can beconceptualized as modules. Both the types (and isolates) of pathogen andthe repertoire of plant receptors may cause different modules to be activatedand affect the magnitude of activation. Two major defense enzymes ofArabidopsis are ALD1 and ICS1/SID2. ALD1 is an aminotransferase needed forproducing the metabolites pipecolic acid, hydroxy-pipecolic acid, and possiblyother defense signals. ICS1/SID2 produces isochorismate, an intermediate inthe synthesis of salicylic acid (SA) and SA-derivatives. Metabolites resulting fromthe activation of these enzymes are found in petiole exudates and may serve aspriming signals for systemic disease resistance in Arabidopsis. Mutants lackingALD1 are known to have reduced SA accumulation. To further investigate therole of ALD1 in relation to the SA-related module, immunity phenotypes ofdouble mutants that disrupt ALD1 and ICS1/SID2 or SA perception by NPR1were compared with each single mutant after infection by differentPseudomonas strains. Exudates collected from these mutants after infectionwere also evaluated for their ability to confer disease resistance when appliedto wild-type plants. During infection with virulent or attenuated strains, the lossof ALD1 does not increase the susceptibility of npr1 or sid2 mutants, suggestingthe main role of ALD1 in this context is in amplifying the SA-related module. Incontrast, after an infection that leads to strong pathogen recognition via thecytoplasmic immune receptor RPS2, ALD1 acts additively with both NPR1 andICS1/SID2 to suppress pathogen growth. The additive effects are observed inearly basal defense responses as well as SA-related events. Thus, there arespecific conditions that dictate whether the modules independently contributeto immunity to provide additive protection during infection. In the exudateexperiments, intact NPR1 and ICS1/SID2, but not ALD1 in the donor plants wereneeded for conferring immunity. Mixing exudates showed that loss of SID2yields exudates that suppress active exudates from wild-type or ald1 plants.