SUPPRESSION AND RESTORATION OF LESION FORMATION IN ARABIDOPSIS ISD MUTANTS

Systemic acquired resistance (SAR) is a broad-spectrum, systemic defen se response that is activated in many plant species after pathogen inf ection, We have previously described Arabidopsis mutants that constitu tively express SAR and concomitantly develop lesions simulating diseas e (lsd), Here, we describe two new mutants, lsd6 and lsd7, that develo p spontaneous necrotic lesions and possess elevated levels of salicyli c acid (SA) as well as heightened disease resistance, similar to the p reviously characterized Isd and accelerated cell death (acd2) mutants, Genetic analysis of lsd6 and lsd7 showed that the mutant phenotypes s egregated as simple dominant traits, When crossed with transgenic Arab idopsis plants containing the SA-degrading enzyme salicylate hydroxyla se, the F-1 progeny showed suppression of both SAR gene expression and resistance. In addition, salicylate hydroxylase suppressed lesion for mation in the F-1 progeny, suggesting that SA or some SA-dependent pro cess may have a role in pathogen-associated cell death, Surprisingly, lesions were restored in the lsd6 F-1 progeny after the application of either 2,6-dichloroisonicotinic acid or SA, Lesions were not restored by treatment with either compound in the lsd7 F-1 plants, Our finding s demonstrate that steps early in the signal transduction pathway lead ing to SAR and disease resistance are potentiated by later events, sug gesting feedback control of lesion formation.