Plant growth-promoting rhizobacteria have been shown to enhance plant tolerance to drought stress through various mechanisms. However, there is limited research on improving drought resistance in alfalfa by genetically modifying PGPR to produce increased levels of cytokinins. Herein, we employed synthetic biology approaches to engineer two novel strains of Sinorhizobium meliloti capable of overproducing trans-Zeatin and investigated their potential in enhancing drought tolerance in alfalfa. Our results demonstrate that alfalfa plants inoculated with these engineered S. meliloti strains exhibited reduced wilting and yellowing while maintaining higher relative water content under drought conditions. The engineered S. meliloti-induced tZ activated the activity of antioxidant enzymes and the accumulation of osmolytes. Additionally, the increased endogenous tZ content in plants alleviated the impact of drought stress on the alfalfa photosynthetic rate. However, under nondrought conditions, inoculation with the engineered S. meliloti strains had no significant effect on alfalfa biomass and nodule formation.

中文翻译：

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深入研究反式玉米素过量生产基因工程苜蓿中华根瘤菌对苜蓿 (Medicago sativa L.) 耐旱性的影响

促进植物生长的根际细菌已被证明可以通过多种机制增强植物对干旱胁迫的耐受性。然而，通过基因改造 PGPR 以产生更高水平的细胞分裂素来提高苜蓿抗旱性的研究有限。在此，我们采用合成生物学方法设计了两种能够过量生产反式玉米素的苜蓿中华根瘤菌新菌株，并研究了它们在增强苜蓿耐旱性方面的潜力。我们的结果表明，接种这些工程苜蓿苜蓿菌株的苜蓿植物表现出减少的萎蔫和黄化，同时在干旱条件下保持较高的相对含水量。转基因苜蓿诱导的 tZ 激活了抗氧化酶的活性和渗透剂的积累。此外，植物内源tZ含量的增加减轻了干旱胁迫对苜蓿光合速率的影响。然而，在非干旱条件下，接种转基因苜蓿菌株对苜蓿生物量和根瘤形成没有显着影响。