Department of Biology, Missouri State University, Springfield, Missouri, USA.
Department of Biology, Missouri State University, Springfield, Missouri, USA
Appl Environ Microbiol. 2021 Apr 27;87(10). doi: 10.1128/AEM.02884-20.
Soybean root nodules are known to contain a high diversity of both rhizobial endophytes and nonrhizobial endophytes (NREs). Nevertheless, the variation of these bacteria among different root nodules within single plants has not been reported. So far, it is unclear whether the selection of NREs among different root nodules within single plants is a random process or is strictly controlled by the host plant to favor a few specific NREs based on their beneficial influence on plant growth. As well, it is also unknown if the relative frequency of NREs within different root nodules is consistent or if it varies based on the location or size of a root nodule. We assessed the microbiomes of 193 individual soybean root nodules from nine plants using high-throughput DNA sequencing. strains occurred in high abundance in all root nodules despite the presence of other soybean-compatible rhizobia, such as , , and other species of in soil. and were the two nonrhizobial genera that were uniformly detected within almost all root nodules, though they were in low abundance. DNA sequences related to other NREs that have frequently been reported, such as , , , and species, were detected in a few nodules. Unlike for , the low abundance and inconsistent occurrence of previously reported NREs among different root nodules within single plants suggest that these microbes are not preferentially selected as endophytes by host plants and most likely play a limited part in plant growth as endophytes. Soybean ( L.) is a valuable food crop that also contributes significantly to soil nitrogen by developing a symbiotic association with nitrogen-fixing rhizobia. Bacterial endophytes (both rhizobial and nonrhizobial) are considered critical for the growth and resilience of the legume host. In the past, several studies have suggested that the selection of bacterial endophytes within root nodules can be influenced by factors such as soil pH, nutrient availability, host plant genotype, and bacterial diversity in soil. However, the influence of size or location of root nodules on the selection of bacterial endophytes within soybean roots is unknown. It is also unclear whether the selection of nonrhizobial endophytes within different root nodules of a single plant is a random process or is strictly regulated by the host. This information can be useful in identifying potential bacterial species for developing bioinoculants that can enhance plant growth and soil nitrogen.
大豆根瘤中已知同时含有丰富的根瘤内生菌和非根瘤内生菌（NRE）。然而，同一植株不同根瘤中的这些细菌的变化尚未有报道。到目前为止，还不清楚同一植株不同根瘤中 NRE 的选择是一个随机过程，还是由宿主植物根据其对植物生长的有益影响，严格控制选择少数特定的 NRE。同样，不同根瘤中 NRE 的相对频率是否一致，或者是否根据根瘤的位置或大小而变化，也不得而知。我们使用高通量 DNA 测序评估了来自 9 株植物的 193 个个体大豆根瘤的微生物组。尽管土壤中存在其他与大豆相容的根瘤菌，如 Rhizobium fredii、Bradyrhizobium japonicum 和其他大豆根瘤菌属的物种，但 菌株在所有根瘤中都大量存在。 和 是在几乎所有根瘤中都均匀检测到的两种非根瘤菌属，尽管它们的丰度较低。在少数根瘤中检测到与其他经常报道的 NRE 相关的 DNA 序列，如 Sinorhizobium fredii、Mesorhizobium loti、Paraburkholderia 和 Burkholderia 属的物种。与 Rhizobium 不同的是，同一植株不同根瘤中以前报道的 NRE 的低丰度和不一致的存在表明，这些微生物不是宿主植物优先选择的内生菌，它们很可能作为内生菌在植物生长中发挥有限的作用。大豆（Glycine max）是一种有价值的粮食作物，通过与固氮根瘤菌形成共生关系，对土壤氮的贡献也很大。细菌内生菌（包括根瘤菌和非根瘤菌）被认为对豆科宿主的生长和恢复力至关重要。过去的研究表明，根瘤内细菌内生菌的选择可能受到土壤 pH 值、养分可用性、宿主植物基因型和土壤中细菌多样性等因素的影响。然而，根瘤大小或位置对大豆根系中细菌内生菌选择的影响尚不清楚。也不清楚同一植株不同根瘤中是否非根瘤内生菌的选择是一个随机过程，还是由宿主严格调控的。这些信息对于鉴定可能用于开发促进植物生长和土壤氮的生物接种剂的潜在细菌物种很有用。
