Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA.
Ann Bot. 2018 Feb 12;121(2):209-220. doi: 10.1093/aob/mcx121.
Polyploidy is known to significantly alter plant genomes, phenotypes and interactions with the abiotic environment, yet the impacts of polyploidy on plant-biotic interactions are less well known. A particularly important plant-biotic interaction is the legume-rhizobia mutualism, in which rhizobia fix atmospheric nitrogen in exchange for carbon provided by legume hosts. This mutualism regulates nutrient cycles in natural ecosystems and provides nitrogen to agricultural environments. Despite the ecological, evolutionary and agricultural importance of plant polyploidy and the legume-rhizobia mutualism, it is not yet fully understood whether plant polyploidy directly alters mutualism traits or the consequences on plant growth.
The aim was to propose a conceptual framework to understand how polyploidy might directly enhance the quantity and quality of rhizobial symbionts hosted by legume plants, resulting in increased host access to fixed nitrogen (N). Mechanistic hypotheses have been devised to examine how polyploidy can directly alter traits that impact the quantity (e.g. nodule number, nodule size, terminal bacteroid differentiation) and quality of symbionts (e.g. nodule environment, partner choice, host sanctions). To evaluate these hypotheses, an exhaustive review of studies testing the effects of plant polyploidy on the mutualism was conducted. In doing so, overall trends were synthesized, highlighting the limited understanding of the mechanisms that underlie variation in results achieved thus far, revealing striking gaps in knowledge and uncovering areas ripe for future research.
Plant polyploidy can immediately alter nodule size, N fixation rate and the identity of rhizobial symbionts hosted by polyploid legumes, but many of the mechanistic hypotheses proposed here, such as bacteroid number and enhancements of the nodule environment, remain unexplored. Although current evidence supports a role of plant polyploidy in enhancing key aspects of the legume-rhizobia mutualism, the underlying mechanisms and effects on host benefit from the mutualism remain unresolved.
多倍体显著改变植物基因组、表型以及与非生物环境的相互作用，但多倍体对植物-生物相互作用的影响知之甚少。植物-生物相互作用中一个特别重要的例子是豆科植物-根瘤菌共生体，其中根瘤菌固定大气氮，以换取豆科植物宿主提供的碳。这种共生体调节自然生态系统的养分循环，并为农业环境提供氮。尽管植物多倍体和豆科植物-根瘤菌共生体具有生态、进化和农业上的重要性，但人们尚不完全了解植物多倍体是否直接改变共生体特征，以及对植物生长的影响。
本研究旨在提出一个概念框架，以了解多倍体如何直接增强豆科植物宿主中根瘤共生体的数量和质量，从而增加宿主对固定氮（N）的利用。设计了机制假设来检验多倍体如何直接改变影响共生体数量（例如，根瘤数量、根瘤大小、末端类菌体分化）和质量（例如，根瘤环境、伙伴选择、宿主制裁）的特征。为了评估这些假设，对测试植物多倍体对共生体影响的研究进行了全面回顾。在这样做的过程中，综合了总体趋势，突出了目前对导致结果变化的机制的理解有限，揭示了知识的显著差距，并揭示了未来研究的热点领域。
植物多倍体可以立即改变根瘤大小、固氮速率和多倍体豆科植物宿主的根瘤共生体身份，但这里提出的许多机制假设，如类菌体数量和根瘤环境的增强，仍未得到探索。尽管目前的证据支持植物多倍体在增强豆科植物-根瘤菌共生体的关键方面的作用，但共生体的潜在机制和对宿主的影响仍未得到解决。
