Summary
The flower is the hallmark of angiosperms and its evolution is key to their diversification. As knowledge of ecological interactions between flowers and their microbial communities (the anthosphere) expands, it becomes increasingly important to consider the evolutionary impacts of these associations and their potential eco‐evolutionary dynamics. In this Viewpoint we synthesize current knowledge of the anthosphere within a multilevel selection framework and illustrate the potential for the extended floral phenotype (the phenotype expressed from the genes of the plant and its associated flower microbes) to evolve. We argue that flower microbes are an important, but understudied, axis of variation that shape floral trait evolution and angiosperm reproductive ecology. We highlight knowledge gaps and discuss approaches that are critical for gaining a deeper understanding of the role microbes play in mediating plant reproduction, ecology, and evolution.
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.
Geographic patterns of genetic variation in wild species reflect the interplay of 21 ecological and evolutionary processes. We assessed genetic variation in three genomes across 22 four North American diploid strawberry taxa, with special emphasis on the gynodioecious F. 23 vesca subsp. bracteata. Specifically, we sequenced one chloroplast (rpoC2) and two 24 mitochondrial (atp8 and atp8-orf225) genes along with several nuclear microsatellite markers. In 25 addition we assessed indicators of breeding system (pollen viability and female frequency) for 26 all taxa. The geographic perspective on the distribution of cytoplasmic and nuclear variation 27 revealed the genetic affiliation of the restricted taxa (F. v. subsp. californica and F. mexicana) 28 with the widespread F. v. subsp. bracteata and identified a hotspot of hybridization within 29 gynodioecious F. v. subsp. bracteata. Higher pollen viability of hermaphrodites was found in the 30 three hermaphroditic taxa relative to the gynodioecious one. Although theoretically predicted to 31 be associated, proportion females within F. v. subsp. bracteata populations, was not correlated 32 with population-level genetic variation, suggesting that the history of hybridization or population 33 size variation is more influential on the distribution of genetic variation than sex ratio in this 34 gynodioecious species. The documented patterns of genetic variation in this complex serve as an 35 important point of reference for future ecological and evolutionary research in diploid Fragaria. 36 37
Premise
Polyploidy is a major genetic driver of ecological and evolutionary processes in plants, yet its effects on plant interactions with mutualistic microbes remain unresolved. The legume–rhizobium symbiosis regulates global nutrient cycles and plays a role in the diversification of legume species. In this mutualism, rhizobia bacteria fix nitrogen in exchange for carbon provided by legume hosts. This exchange occurs inside root nodules, which house bacterial cells and represent the interface of legume–rhizobium interactions. Although polyploidy may directly impact the legume–rhizobium mutualism, no studies have explored how it alters the internal structure of nodules.
Methods
We created synthetic autotetraploids using Medicago sativa subsp. caerulea. Neotetraploid plants and their diploid progenitors were singly inoculated with two strains of rhizobia, Sinorhizobium meliloti and S. medicae. Confocal microscopy was used to quantify internal traits of nodules produced by diploid and neotetraploid plants.
Results
Autotetraploid plants produced larger nodules with larger nitrogen fixation zones than diploids for both strains of rhizobia, although the significance of these differences was limited by power. Neotetraploid M. sativa subsp. caerulea plants also produced symbiosomes that were significantly larger, nearly twice the size, than those present in diploids.
Conclusions
This study sheds light on how polyploidy directly affects a plant–bacterium mutualism and uncovers novel mechanisms. Changes in plant–microbe interactions that directly result from polyploidy likely contribute to the increased ability of polyploid legumes to establish in diverse environments.
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