Mol Plant Microbe Interact. 2014 Jul;27(7):655-63. doi: 10.1094/MPMI-01-14-0010-R.
The interaction between plants and plant-growth-promoting rhizobacteria (PGPR) is a complex, reciprocal process. On the one hand, plant compounds such as carbohydrates and amino acids serve as energy sources for PGPR. On the other hand, PGPR promote plant growth by synthesizing plant hormones and increasing mineral availability in the soil. Here, we evaluated the growth-promoting activity of Bacillus subtilis OKB105 and identified genes associated with this activity. The genes yecA (encoding a putative amino acid/polyamine permease) and speB (encoding agmatinase) are involved in the secretion or synthesis of polyamine in B. subtilis OKB105. Disruption of either gene abolished the growth-promoting activity of the bacterium, which was restored when polyamine synthesis was complemented. Moreover, high-performance liquid chromatography analysis of culture filtrates of OKB105 and its derivatives demonstrated that spermidine, a common polyamine, is the pivotal plant-growth-promoting compound. In addition, real-time polymerase chain reaction analysis revealed that treatment with B. subtilis OKB105 induced expansin gene (Nt-EXPA1 and Nt-EXPA2) expression and inhibited the expression of the ethylene biosynthesis gene ACO1. Furthermore, enzyme-linked immunosorbent assay analysis showed that the ethylene content in plant root cells decreased in response to spermidine produced by OKB105. Therefore, during plant interactions, OKB105 may produce and secrete spermidine, which induces expansin production and lowers ethylene levels.
植物与植物促生根际细菌（PGPR）之间的相互作用是一个复杂的、相互的过程。一方面，植物化合物，如碳水化合物和氨基酸，作为 PGPR 的能量来源。另一方面，PGPR 通过合成植物激素和增加土壤中矿物质的可用性来促进植物生长。在这里，我们评估了枯草芽孢杆菌 OKB105 的促生长活性，并鉴定了与该活性相关的基因。yecA 基因（编码一种假定的氨基酸/多胺渗透酶）和 speB 基因（编码胍丁胺酶）参与枯草芽孢杆菌 OKB105 中多胺的分泌或合成。这两个基因的缺失都消除了细菌的促生长活性，而当多胺合成得到补充时，这种活性就得到了恢复。此外，对 OKB105 及其衍生物的培养滤液进行高效液相色谱分析表明，腐胺是一种常见的多胺，是促进植物生长的关键化合物。此外，实时聚合酶链反应分析显示，枯草芽孢杆菌 OKB105 的处理诱导了扩张蛋白基因（Nt-EXPA1 和 Nt-EXPA2）的表达，并抑制了乙烯生物合成基因 ACO1 的表达。此外，酶联免疫吸附测定分析表明，植物根细胞中的乙烯含量随着 OKB105 产生的腐胺而降低。因此，在植物相互作用过程中，OKB105 可能产生和分泌腐胺，诱导扩张蛋白的产生并降低乙烯水平。
