John Innes Centre, Norwich Research Park, Norwich, UK.
Mol Plant Microbe Interact. 2012 Feb;25(2):250-8. doi: 10.1094/MPMI-08-11-0211.
Rhizobium leguminosarum bv. viciae can attach to the roots of legume and non-legume plants. We wanted to determine whether root exudates could affect in vitro surface attachment in a confocal microscopy assay. Root exudate from pea, other legumes, wheat, and Arabidopsis induced R. leguminosarum bv. viciae to attach end-on (in a polar manner) to glass in hexagonal close-packed arrays, rather than attaching along their long axis. This did not involve a reorientation but was probably due to altered growth. The polar attachment involves a novel bacterial component because it occurred in mutants lacking a symbiosis plasmid (and hence nodulation genes) and polar glucomannan. The major surface (acidic) exopolysaccharide was required, and mutations affecting exported proteins and flagella delayed but did not block polar attachment. The polar attachment activity was purified as a high molecular weight fraction from pea root exudate and is an arabinogalactan protein (AGP) based on its carbohydrate content, reactivity with AGP-specific monoclonal antibodies and Yariv reagent, and sensitivity to enzymes that degrade proteins and carbohydrates. We propose that this novel mode of AGP-induced attachment may be important for growth of these bacteria on the roots of both legumes and non-legumes.
根瘤菌可以附着在豆科和非豆科植物的根部。我们想确定根分泌物是否会影响共聚焦显微镜检测中的体外表面附着。豌豆、其他豆科植物、小麦和拟南芥的根分泌物诱导根瘤菌 bv. 豌豆以六方最密堆积的方式端对端（以极性方式）附着在玻璃上，而不是沿着它们的长轴附着。这不是重新定向，而是可能由于生长方式的改变。极性附着涉及到一个新的细菌成分，因为它发生在缺乏共生质粒（因此也缺乏结瘤基因）和极性葡甘露聚糖的突变体中。主要的表面（酸性）多糖是必需的，并且影响分泌蛋白和鞭毛的突变会延迟但不会阻止极性附着。从豌豆根分泌物中纯化出一种高分子量的极性附着活性物质，该物质是一种阿拉伯半乳聚糖蛋白 (AGP)，其碳水化合物含量、与 AGP 特异性单克隆抗体和 Yariv 试剂的反应性以及对降解蛋白质和碳水化合物的酶的敏感性表明了这一点。我们提出，这种新型的 AGP 诱导附着模式可能对这些细菌在豆科和非豆科植物根部的生长很重要。
