Data_Sheet_2_MtCAS31 Aids Symbiotic Nitrogen Fixation by Protecting the Leghemoglobin MtLb120-1 Under Drought Stress in Medicago truncatula.XLSX

Symbiotic nitrogen fixation (SNF) in legume root nodules injects millions of tons of nitrogen into agricultural lands and provides ammonia to non-legume crops under N-deficient conditions. During plant growth and development, environmental stresses, such as drought, salt, cold, and heat stress are unavoidable. This raises an interesting question as to how the legumes cope with the environmental stress along with SNF. Under drought stress, dehydrin proteins are accumulated, which function as protein protector and osmotic substances. In this study, we found that the dehydrin MtCAS31 (cold-acclimation-specific 31) functions in SNF in Medicago truncatula during drought stress. We found that MtCAS31 is expressed in nodules and interacts with leghemoglobin MtLb120-1. The interaction between the two proteins protects MtLb120-1 from denaturation under thermal stress in vivo. Compared to wild type, cas31 mutants display a lower nitrogenase activity, a lower ATP/ADP ratio, higher expression of nodule senescence genes and higher accumulation of amyloplasts under dehydration conditions. The results suggested that MtCAS31 protects MtLb120-1 from the damage of drought stress. We identified a new function for dehydrins in SNF under drought stress, which enriches the understanding of the molecular mechanism of dehydrins.

豆科植物根瘤中的共生固氮（Symbiotic nitrogen fixation, SNF）可向农田输入数百万吨氮素，并在缺氮条件下为非豆科作物提供氨源。在植物生长发育过程中，干旱、盐渍、低温及高温等环境胁迫难以避免。由此引出一个值得探究的科学问题：豆科植物如何在开展共生固氮的同时应对环境胁迫？干旱胁迫下，脱水素蛋白（dehydrin proteins）会大量积累，兼具蛋白质保护剂与渗透调节物质的功能。本研究发现，蒺藜苜蓿（Medicago truncatula）中的脱水素MtCAS31（cold-acclimation-specific 31）在干旱胁迫下参与共生固氮过程。研究显示，MtCAS31在根瘤中表达，并与豆血红蛋白（leghemoglobin）MtLb120-1发生相互作用；该蛋白互作可在体内保护MtLb120-1免受热胁迫导致的变性。与野生型相比，脱水处理条件下，cas31突变体的固氮酶活性更低、ATP/ADP比值更小，根瘤衰老基因的表达量更高，造粉体积累量更多。研究结果表明，MtCAS31可保护MtLb120-1免受干旱胁迫的损伤。本研究揭示了脱水素在干旱胁迫下共生固氮过程中的全新功能，丰富了学界对脱水素分子作用机制的认知。