Department of Biological Science, Florida State University, Tallahassee, FL 32306-4370, USA.
Mol Plant Microbe Interact. 2013 Sep;26(9):1089-105. doi: 10.1094/MPMI-03-13-0087-R.
The acidic polysaccharide succinoglycan produced by the nitrogen-fixing rhizobial symbiont Sinorhizobium meliloti 1021 is required for this bacterium to invade the host plant Medicago truncatula and to efficiently invade the host plant M. sativa (alfalfa). The β-glucanase enzyme encoded by exoK has previously been demonstrated to cleave succinoglycan and participate in producing the low molecular weight form of this polysaccharide. Here, we show that exoK is required for efficient S. meliloti invasion of both M. truncatula and alfalfa. Deletion mutants of exoK have a substantial reduction in symbiotic productivity on both of these plant hosts. Insertion mutants of exoK have an even less productive symbiosis than the deletion mutants with the host M. truncatula that is caused by a secondary effect of the insertion itself, and may be due to a polar effect on the expression of the downstream exoLAMON genes.
固氮根瘤菌共生体苜蓿中华根瘤菌 1021 产生的酸性多糖琥珀聚糖对于该细菌入侵宿主植物紫花苜蓿和有效入侵宿主植物 M. sativa（紫花苜蓿）是必需的。先前已经证明，外切 β-葡聚糖酶酶编码基因 exoK 可以切割琥珀聚糖并参与产生这种多糖的低分子量形式。在这里，我们表明 exoK 对于 S. meliloti 对紫花苜蓿和紫花苜蓿的有效入侵是必需的。exoK 的缺失突变体在这两种植物宿主上的共生生产力都有显著降低。插入突变体的 exoK 的共生作用比缺失突变体的生产力更低，这是由于插入本身的二次效应引起的，并且可能是由于对下游 exoLAMON 基因表达的极性效应。
