LESION SIMULATING DISEASE1, ENHANCED DISEASE SUSCEPTIBILITY1, and PHYTOALEXIN DEFICIENT4 Conditionally Regulate Cellular Signaling Homeostasis, Photosynthesis, Water Use Efficiency, and Seed Yield in Arabidopsis

There is growing evidence that for a comprehensive insight into the function of plant genes, it is crucial to assess their functionalities under a wide range of conditions. In this study, we examined the role of LESION SIMULATING DISEASE1 (LSD1), ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1), and PHYTOALEXIN DEFICIENT4 (PAD4) in the regulation of photosynthesis, water use efficiency, reactive oxygen species/hormonal homeostasis, and seed yield in Arabidopsis (Arabidopsis thaliana) grown in the laboratory and in the field. We demonstrate that the LSD1 null mutant (lsd1), which is known to exhibit a runaway cell death in nonpermissive conditions, proves to be more tolerant to combined drought and high-light stress than the wild type. Moreover, depending on growing conditions, it shows variations in water use efficiency, salicylic acid and hydrogen peroxide concentrations, photosystem II maximum efficiency, and transcription profiles. However, despite these changes, lsd1 demonstrates similar seed yield under all tested conditions. All of these traits depend on EDS1 and PAD4. The differences in the pathways prevailing in the lsd1 in various growing environments are manifested by the significantly smaller number of transcripts deregulated in the field compared with the laboratory, with only 43 commonly regulated genes. Our data indicate that LSD1, EDS1, and PAD4 participate in the regulation of various molecular and physiological processes that influence Arabidopsis fitness. On the basis of these results, we emphasize that the function of such important regulators as LSD1, EDS1, and PAD4 should be studied not only under stable laboratory conditions, but also in the environment abounding in multiple stresses.