Abstract
Climate change and enhanced pollution levels are subjecting plants and crops to an increased number of different stressors, simultaneously or sequentially, generating conditions of multifactorial stress combination (MFSC). Although MFSC was shown to severely diminish plant growth, yield, and survival, how plants acclimate to increased levels of stress complexity is largely unknown. Here, we reveal that the Arabidopsis thaliana transcriptional regulator basic helix-loop-helix 35 (bHLH35) is required for plant acclimation to a specific set of MFSC conditions that includes a combination of salinity, excess light, and heat, occurring simultaneously (but not to each of these stresses applied individually or in any other combination). Under the three-stress combination, bHLH35 interacts with no apical meristem/transcription activator factor/cup-shaped cotyledon 69 (NAC069), binds the promoter of lateral organ boundaries domain 31 (LBD31), and regulates the expression of transcripts involved in flavonoid metabolism and ethylene signaling. Our findings uncover a high degree of specificity in plant responses to stress combination, suggesting that different conditions of MFSC could require the function of specific genetic programs for acclimation.