Plant Science Division, University of Missouri, Columbia, MO 65211, USA.
King Abdul Aziz University, 21589 Jeddah, Saudi Arabia.
Int J Mol Sci. 2019 Mar 3;20(5):1091. doi: 10.3390/ijms20051091.
Pigeon pea ( Millspaugh) is cultivated widely in semiarid agricultural regions in over 90 countries around the world. This important legume can enter into symbiotic associations with a wide range of rhizobia including and fast-growing rhizobia. In comparison with other major legumes such as soybean and common bean, only limited information is available on the symbiotic interaction of pigeon pea with rhizobia. In this study, we investigated the ability of two classical soybean symbionts- USDA191 and USDA110-and their type 3 secretion system (T3SS) mutants, to nodulate pigeon pea. Both USDA191 and a T3SS mutant RCB26 formed nitrogen-fixing nodules on pigeon pea. Inoculation of pigeon pea roots with USDA110 and Δ136 (a T3SS mutant) resulted in the formation of Fix- and Fix+ nodules, respectively. Light and transmission electron microscopy of Fix- nodules initiated by USDA110 revealed the complete absence of rhizobia within these nodules. In contrast, Fix+ nodules formed by Δ136 revealed a central region that was completely filled with rhizobia. Ultrastructural investigation revealed the presence of numerous bacteroids surrounded by peribacteroid membranes in the infected cells. Analysis of nodule proteins by one- and two-dimensional gel electrophoresis revealed that leghemoglobin was absent in USDA110 nodules, while it was abundantly present in Δ136 nodules. Results of competitive nodulation assays indicated that Δ136 had greater competitiveness for nodulation on pigeon pea than did the wild type strain. Our results suggest that this T3SS mutant of , due to its greater competitiveness and ability to form Fix+ nodules, could be exploited as a potential inoculant to boost pigeon pea productivity.
兵豆（Millspaugh）广泛种植于全世界 90 多个国家的半干旱农业区。这种重要的豆科作物可以与包括中慢生根瘤菌和快生根瘤菌在内的广泛的根瘤菌形成共生关系。与大豆和普通菜豆等其他主要豆科植物相比，关于兵豆与根瘤菌的共生互作，仅有有限的信息。在这项研究中，我们研究了两个经典的大豆共生体——USDA191 和 USDA110 及其 III 型分泌系统（T3SS）突变体与兵豆共生的能力。USDA191 和一个 T3SS 突变体 RCB26 都能在兵豆上形成固氮根瘤。USDA110 和 T3SS 突变体 Δ136 接种兵豆根后，分别形成 Fix-和 Fix+根瘤。USDA110 诱导的 Fix-根瘤的光镜和透射电镜观察表明，这些根瘤内完全没有根瘤菌。相比之下，由 Δ136 形成的 Fix+根瘤显示出一个完全充满根瘤菌的中央区域。超微结构研究表明，在受感染的细胞中，存在大量被周质膜包围的类菌体。通过一维和二维凝胶电泳分析根瘤蛋白表明，USDA110 根瘤中不存在豆血红蛋白，而 Δ136 根瘤中则大量存在。竞争结瘤试验的结果表明，与野生型菌株相比，Δ136 对兵豆结瘤具有更强的竞争力。我们的结果表明，由于该 T3SS 突变体能形成 Fix+根瘤且具有更强的竞争力，因此可能被开发为一种潜在的接种剂来提高兵豆的生产力。
