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Limitation of Nocturnal ATP Import into Chloroplasts Seems to Affect Hormonal Crosstalk, Prime Defense, and Enhance Disease Resistance in Arabidopsis thaliana

¹Plant Biochemistry & Molecular Biology Group, Department of Plant Physiology, RWTH Aachen University, Aachen, 52056, Germany; ²Department of Plant Physiology, Kaiserslautern Tech, Kaiserslautern, 67663, Germany; ³Department of Plant Biochemistry, Albrecht von Haller Institute for Plant Sciences, Georg August University, Göttingen 37077, Germany

When grown under short-day conditions at low light, leaves of an Arabidopsis thaliana (accession Col-0) mutant with defects in the two genes encoding plastid ATP/ADP antiporters (so-called ntt1-2 null mutants) display a variety of physiological changes. These include the formation of necrotic lesions and the accumulation of hydrogen peroxide in the leaves. Here, we show that, under short-day conditions, leaves of the ntt1-2 mutant display enhanced resistance to Hyaloperonospora arabidopsidis, Botrytis cinerea, and Pseudomonas syringae pv. tomato DC3000. Resistance to these pathogens was associated with constitutively elevated levels of the plant hormone salicylic acid and, eventually, jasmonic acid, and constitutive or primed activation after pathogen attack of various defense genes that are dependent on these hormones. In addition, the antagonistic crosstalk between the salicylic acid and jasmonic acid signaling pathways seems to be affected in ntt1-2. Because the enhanced resistance of ntt1-2 to H. arabidopsidis was not seen when the mutant was grown under long-day conditions, our findings argue that nocturnal ATP import into chloroplasts is crucial to keep A. thaliana from runaway activation of pathogen resistance.