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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Eukaryotic control on bacterial cell cycle and differentiation in the Rhizobium-legume symbiosis
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Eukaryotic control on bacterial cell cycle and differentiation in the Rhizobium-legume symbiosis

机译：真核生物对根瘤菌-豆科植物共生中细菌细胞周期和分化的控制

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摘要

Symbiosis between legumes and Rhizobium bacteria leads to the formation of root nodules where bacteria in the infected plant cells are converted into nitrogen-fixing bacteroids. Nodules with a persistent meristem are indeterminate, whereas nodules without meristem are determinate. The symbiotic plant cells in both nodule types are polyploid because of several cycles of endoreduplication (genome replication without mitosis and cytokinesis) and grow consequently to extreme sizes. Here we demonstrate that differentiation of bacteroids in indeterminate nodules of Medicago and related legumes from the galegoid clade shows remarkable similarity to host cell differentiation. During bacteroid maturation, repeated DNA replication without cytokinesis results in extensive amplification of the entire bacterial genome and elongation of bacteria. This finding reveals a positive correlation in prokaryotes between DNA content and cell size, similar to that in eukaryotes. These polyploid bacteroids are metabolically functional but display increased membrane permeability and are nonviable, because they lose their ability to resume growth. In contrast, bacteroids in determinate nodules of the nongalegoid legumes lotus and bean are comparable to free-living bacteria in their genomic DNA content, cell size, and viability. Using recombinant Rhizobium strains nodulating both legume types, we show that bacteroid differentiation is controlled by the host plant. Plant factors present in nodules of galegoid legumes but absent from nodules of nongalegoid legumes block bacterial cell division and trigger endoreduplication cycles, thereby forcing the endosymbionts toward a terminally differentiated state. Hence, Medicago and related legumes have evolved a mechanism to dominate the symbiosis.
机译：豆科植物和根瘤菌之间的共生导致根瘤的形成，受感染植物细胞中的细菌被转化为固氮类细菌。具有分生组织的结节是不确定的，而没有分生组织的结节是确定的。两种结节类型的共生植物细胞都是多倍体，因为它们具有多个内核复制周期（基因组复制而无有丝分裂和胞质分裂），因此生长至极大的尺寸。在这里，我们证明了从半球形的进化支中，不确定的紫花苜蓿和相关豆类瘤中的类细菌分化表现出与宿主细胞分化的显着相似性。在类细菌成熟过程中，重复的DNA复制而没有胞质分裂作用会导致整个细菌基因组的广泛扩增和细菌的延伸。这一发现揭示了原核生物中DNA含量与细胞大小之间的正相关，与真核生物中相似。这些多倍体类细菌具有代谢功能，但显示出增加的膜通透性并且不可行，因为它们失去了恢复生长的能力。相反，在非半豆科植物豆科植物的确定结节中，类杆菌在基因组DNA含量，细胞大小和生存力方面可与自由活动细菌媲美。使用结瘤两种豆科植物类型的重组根瘤菌菌株，我们表明类细菌的分化是由宿主植物控制的。植物因子存在于galegoid豆科植物的结节中，但不存在于非galegoid豆科植物的结节中，会阻止细菌细胞分裂并触发内复制过程，从而迫使内共生菌趋向终末分化状态。因此，紫花苜蓿和相关豆科植物已经进化出一种控制共生的机制。

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