Arabidopsis acclimation to daily environmental fluctuations converts a defense response regulator into a susceptibility factor toward Sclerotinia.

Acclimation enables plants to adjust to immediate environmental fluctuations and is therefore key to the resilience of plant disease resistance in a time of climate change. Here, we report on the acclimation of Arabidopsis thaliana quantitative immune responses against the fungal pathogen Sclerotinia sclerotiorum to daily environmental fluctuations. We analyzed disease resistance phenotypes and global gene expression in plants grown in three acclimation regimes, revealing the rewiring of regulatory networks during this process. We identified pathogen-induced genes weakly sensitive to acclimation as promising bases for acclimation-proof immunity. Fluctuations in Mediterranean-like acclimation resulted in an increased disease susceptibility and the misregulation of many pathogen-responsive genes. We identified A. thaliana mutants in novel immune components contributing positively to quantitative disease resistance following temperate but not Mediterranean acclimation. Quantitative disease resistance was maintained under Mediterranean acclimation in NAC42-like mutants and associated with a switch in the repertoire of pathogen-responsive targets of this transcription factor. Our work reveals the role of immune gene networks' plasticity in acclimation and suggests new strategies to maintain plant immune function in a warming climate.