Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, PR China; University of Chinese Academy of Sciences, Beijing 100049, PR China.
Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, PR China.
Plant Sci. 2019 Jun;283:311-320. doi: 10.1016/j.plantsci.2019.03.011. Epub 2019 Mar 19.
Thiamine is a pivotal primary metabolite which is indispensable to all organisms. Although its biosynthetic pathway has been well documented, the mechanism by which thiamine influences the legume-rhizobium symbiosis remains uncertain. Here, we used overexpressing transgenic plants, mutants and grafting experiments to investigate the roles played by thiamine in Lotus japonicus nodulation. ljthic mutants displayed lethal phenotypes and the defect could be overcome by supplementation of thiamine or by overexpression of LjTHIC. Reciprocal grafting between L. japonicus wild-type Gifu B-129 and ljthic showed that the photosynthetic products of the aerial part made a major contribution to overcoming the nodulation defect in ljthic. Overexpression of LjTHIC in Lotus japonicus (OE-LjTHIC) decreased shoot growth and increased the activity of the enzymes 2-oxoglutarate dehydrogenase and pyruvate dehydrogenase. OE-LjTHIC plants exhibited an increase in the number of infection threads and also developed more nodules, which were of smaller size but unchanged nitrogenase activity compared to the wildtype. Taken together, our results suggest that endogenous thiamine produced via LjTHIC acts as an essential nutrient provided by the host plant for rhizobial infection and nodule growth in the Lotus japonicus - rhizobium interaction.
硫胺素是一种至关重要的初级代谢物，是所有生物所必需的。尽管其生物合成途径已经得到充分证实，但硫胺素影响豆科植物-根瘤菌共生的机制仍不清楚。在这里，我们使用过表达转基因植物、突变体和嫁接实验来研究硫胺素在百脉根结瘤中的作用。 ljthic 突变体表现出致命表型，硫胺素的补充或 LjTHIC 的过表达可以克服该缺陷。百脉根野生型 Gifu B-129 和 ljthic 之间的互惠嫁接表明，地上部分的光合产物对克服 ljthic 的结瘤缺陷有主要贡献。LjTHIC 在百脉根中的过表达（OE-LjTHIC）降低了地上部分的生长，增加了 2-氧戊二酸脱氢酶和丙酮酸脱氢酶的活性。OE-LjTHIC 植物的侵染线数量增加，结瘤数量也增加，但与野生型相比，结瘤的大小减小，但固氮酶活性不变。总之，我们的结果表明，通过 LjTHIC 产生的内源性硫胺素作为宿主植物为根瘤菌感染和百脉根-根瘤菌相互作用中根瘤的生长提供的必需营养物质。
