Deciphering Arabidopsis thaliana Acclimation to Sublethal Combined Abiotic Stresses

Plants are frequently exposed to environmental challenges. Responses to sub-lethal abiotic stress combinations are complex and often distinct from responses to individual stresses and remain poorly understood. Investigating traits and molecular factors mediating acclimation to stress combinations is essential for the development of climate change-resilient field crops. Here, we studied the morphological, physiological, and molecular responses of Arabidopsis thaliana to i) co-occurring high temperature and drought and ii) flooding sequentially followed by drought, both of which have increased in frequency due to climate change. A set of 15 physiological and morphological traits were assessed during single and combined stresses. By combining these comprehensive trait analyses with transcriptome characterization, we established the generally additive effects of simultaneous or sequential stresses on plant morphology and physiology compared to the corresponding individual stresses. Although drought had a mild effect in both stress combinations, a unique transcriptome signature emerged upon combination with high temperature simultaneously or flooding sequentially. Molecular processes identified as important for multi-stress resilience included plastid-nucleus communication, ABA signaling and photo-acclimation. Based on the RNA-seq data, a set of 39 genes was identified as potential multi-stress response regulators. Mutants were tested to validate their contribution to plant survival and phenotypic acclimation under combined stress. We confirmed the involvement of several genes in regulating phenotypic acclimation traits. Among the novel identified factors are EARLY FLOWERING 6 (ELF6) and ARABIDOPSIS TOXICOS EN LEVADURA (ATL80), with significant effects on plant growth, leaf development and plant survival (wilting) during high-temperature drought and post-submergence drought respectively.