USDA-ARS, Plant Genetics Research Unit, 105 Curtis Hall, University of Missouri, Columbia, MO, 65211, USA.
Division of Plant Sciences, University of Missouri, Columbia, MO, 65211, USA.
Sci Rep. 2018 Feb 5;8(1):2367. doi: 10.1038/s41598-018-20919-8.
Nitrogen-fixing nodules, which are also major sites of sulfur assimilation, contribute significantly to the sulfur needs of whole soybean plants. Nodules are the predominant sites for cysteine accumulation and the activity of O-acetylserine(thiol)lyase (OASS) is central to the sulfur assimilation process in plants. Here, we examined the impact of overexpressing OASS on soybean nodulation and nodule metabolome. Overexpression of OASS did not affect the nodule number, but negatively impacted plant growth. HPLC measurement of antioxidant metabolites demonstrated that levels of cysteine, glutathione, and homoglutathione nearly doubled in OASS overexpressing nodules when compared to control nodules. Metabolite profiling by LC-MS and GC-MS demonstrated that several metabolites related to serine, aspartate, glutamate, and branched-chain amino acid pathways were significantly elevated in OASS overexpressing nodules. Striking differences were also observed in the flavonoid levels between the OASS overexpressing and control soybean nodules. Our results suggest that OASS overexpressing plants compensate for the increase in carbon requirement for sulfur assimilation by reducing the biosynthesis of some amino acids, and by replenishing the TCA cycle through fatty acid hydrolysis. These data may indicate that in OASS overexpressing soybean nodules there is a moderate decease in the supply of energy metabolites to the nodule, which is then compensated by the degradation of cellular components to meet the needs of the nodule energy metabolism.
固氮根瘤也是硫同化的主要部位，对大豆植株的硫需求有重要贡献。根瘤是半胱氨酸积累的主要部位，O-乙酰丝氨酸（硫代）裂解酶（OASS）的活性是植物硫同化过程的核心。在这里，我们研究了过表达 OASS 对大豆结瘤和根瘤代谢组的影响。过表达 OASS 不会影响根瘤数量，但对植物生长有负面影响。高效液相色谱法测量抗氧化代谢物表明，与对照根瘤相比，OASS 过表达根瘤中的半胱氨酸、谷胱甘肽和同型谷胱甘肽水平几乎翻了一番。通过 LC-MS 和 GC-MS 进行的代谢物分析表明，与丝氨酸、天冬氨酸、谷氨酸和支链氨基酸途径相关的几种代谢物在 OASS 过表达根瘤中显著升高。OASS 过表达和对照大豆根瘤中的类黄酮水平也存在显著差异。我们的结果表明，OASS 过表达植物通过减少一些氨基酸的生物合成，并通过脂肪酸水解补充 TCA 循环，来补偿硫同化对碳需求的增加。这些数据可能表明，在 OASS 过表达大豆根瘤中，向根瘤供应的能量代谢物适度减少，然后通过降解细胞成分来补偿根瘤能量代谢的需求。
