Legume sanctions and the evolution of symbiotic cooperation by rhizobia
Legume sanctions and the evolution of symbiotic cooperation by rhizobia
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DOI：
10.1086/316994
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发表时间：
2000-12-01
影响因子：
2.9
通讯作者：
Denison, RF
中科院分区：
文献类型：
--
作者：
Denison, RF
豆科植物-根瘤菌共生是研究限制微生物共生体进化为寄生物的因素的理想模型。豆科植物无法一致地识别寄生根瘤菌，一旦在植物细胞内建立，就利用植物资源进行自己的繁殖，而不是固定N-2。根瘤菌寄生的进化，部分是由感染同一种植物的多个根瘤菌株之间的竞争驱动的，可能会被感染后的豆类制裁所抵消。根瘤菌欺骗的生化选择和豆类制裁的进化效应取决于与根瘤类型相关的根瘤菌生活史的差异。在根瘤生长有限的豆科植物中，根瘤菌在分化成固氮类杆菌后通常保留繁殖能力。对单个类杆菌的制裁（例如，酸水解酶）因此将选择合作根瘤菌。在不确定生长的根瘤中，类杆菌通常失去繁殖能力，因此豆类对类杆菌的制裁不会对根瘤菌的进化产生影响。全结核制裁（例如，减少根瘤O-2渗透性）可能是有效的，通过亲属选择未分化的根瘤菌，坚持在不确定的根瘤和根瘤衰老后补充土壤种群。混合结核可能降低全结核制裁的效力。在实地条件下，混合结核的出现频率尚不清楚。
The legume-rhizobium symbiosis is an ideal model for studying the factors that limit the evolution of microbial mutualists into parasites. Legumes are unable to consistently recognize parasitic rhizobia that, once established inside plant cells, use plant resources for their own reproduction rather than for N-2 fixation. Evolution of parasitism in rhizobia, driven partly by competition among multiple rhizobial strains infecting the same plant, may be countered by postinfection legume sanctions. Both the biochemical options for rhizobial cheating and the evolutionary effect of legume sanctions depend on differences in rhizobial life history associated with nodule type. In legumes with determinate nodule growth, rhizobia typically retain the ability to reproduce after differentiating into N-2-fixing bacteroids. Sanctions against individual bacteroids (e.g., acid hydrolases) would therefore select for cooperative rhizobia. In nodules with indeterminate growth, bacteroids generally lose the ability to reproduce, so legume sanctions against bacteroids would have no effect on rhizobial evolution. Whole-nodule sanctions (e.g., decreased nodule O-2 permeability) could be effective, via kin selection of undifferentiated rhizobia that persist in indeterminate nodules and replenish soil populations after nodule senescence. Mixed nodules could reduce the effectiveness of whole-nodule sanctions. The frequency of mixed nodules under field conditions is unknown.