Wasala Sulochana K, Brown Amanda M V, Kang Jiwon, Howe Dana K, Peetz Amy B, Zasada Inga A, Denver Dee R
Department of Integrative Biology, Oregon State University, Corvallis, OR, United States.
Department of Biological Sciences, Texas Tech University, Lubbock, TX, United States.
Front Microbiol. 2019 May 7;10:964. doi: 10.3389/fmicb.2019.00964. eCollection 2019.
The bacterial endosymbiont interacts with different invertebrate hosts, engaging in diverse symbiotic relationships. is often a reproductive parasite in arthropods, but an obligate mutualist in filarial nematodes. was recently discovered in plant-parasitic nematodes, and, is thus far known in just two genera and , yet the symbiont's function remains unknown. The occurrence of in these economically important plant pests offers an unexplored biocontrol strategy. However, development of -based biocontrol requires an improved understanding of symbiont-host functional interactions and the symbiont's prevalence among nematode field populations. This study used a molecular-genetic approach to assess the prevalence of a lineage (wPpe) in 32 field populations of Populations were examined from eight different plant species in Washington, Oregon, and California. Nematodes were also screened for the endosymbiotic bacterium (cPpe) that was recently shown to co-infect . Results identified wPpe in 9/32 and cPpe in 1/32 of field populations analyzed. No co-infection was observed in field populations. was detected in nematodes from 4/8 plant-hosts examined (raspberry, strawberry, clover, and lily), and in all three states surveyed. was detected in nematodes from mint in Washington. In the wPpe-infected populations collected from raspberry, the prevalence of wPpe infection ranged from 11 to 58%. This pattern is unlike that in filarial nematodes where is an obligate mutualist and occurs in 100% of the host. Further analysis of wPpe-infected populations revealed female-skewed sex ratios (up to 96%), with the degree of skew positively correlating with wPpe prevalence. Uninfected nematode populations had approximately equal numbers of males and females. Comparisons of 54 wPpe 16S ribosomal RNA sequences revealed high similarity across the geographic isolates, with 45 of 54 isolates being identical at this locus. The complete absence of wPpe among some populations and low prevalence in others suggest that this endosymbiont is not an obligate mutualist of . The observed sex ratio bias in wPpe-infected nematode populations is similar to that observed in arthropods where acts as a reproductive manipulator, raising the question of a similar role in plant-parasitic nematodes.
这种细菌内共生体与不同的无脊椎动物宿主相互作用，形成多种共生关系。它在节肢动物中通常是一种生殖寄生虫，但在丝虫线虫中是专性互利共生体。最近在植物寄生线虫中发现了它，目前仅在两个属中已知，但其共生功能仍不清楚。在这些具有经济重要性的植物害虫中发现这种共生体，为生物防治提供了一种尚未探索的策略。然而，基于该共生体的生物防治发展需要更好地理解共生体与宿主的功能相互作用以及该共生体在田间线虫种群中的流行情况。本研究采用分子遗传学方法评估了32个田间种群中某一线粒体谱系（wPpe）的流行情况。这些种群来自华盛顿、俄勒冈和加利福尼亚的8种不同植物。还对线虫进行了筛选，以检测最近发现可共同感染的内共生细菌（cPpe）。结果在分析的32个田间种群中，9个检测到wPpe，1个检测到cPpe。在田间种群中未观察到共同感染。在所检测的8种植物宿主（树莓、草莓、三叶草和百合）中的4种以及所有三个调查州的线虫中都检测到了该共生体。在华盛顿州薄荷的线虫中检测到了该共生体。在从树莓采集的感染wPpe的种群中，wPpe感染率在11%至58%之间。这种模式与丝虫线虫不同，在丝虫线虫中该共生体是专性互利共生体，且在100%的宿主中存在。对感染wPpe的种群的进一步分析显示，性别比例偏向雌性（高达96%），偏斜程度与wPpe流行率呈正相关。未感染的线虫种群中雄性和雌性数量大致相等。对54个wPpe 16S核糖体RNA序列的比较显示，不同地理分离株之间具有高度相似性，54个分离株中有45个在该位点相同。一些种群中完全没有wPpe，而另一些种群中流行率较低，这表明这种内共生体不是该线虫的专性互利共生体。在感染wPpe的线虫种群中观察到的性别比例偏差与在节肢动物中观察到的相似，在节肢动物中该共生体作为生殖操纵者，这就提出了它在植物寄生线虫中是否有类似作用的问题。
