Floral organs act as environmental filters and interact with pollinators to structure the yellow monkeyflower (Mimulus guttatus) floral microbiome

Abstract

Assembly of microbial communities is the result of neutral and selective processes. However, the relative importance of these processes is still debated. Microbial communities of flowers, in particular, have gained recent attention because of their potential impact to plant fitness and plant-pollinator interactions. However, the role of selection and dispersal in the assembly of these communities remains poorly understood. We evaluated the role of pollinator-mediated dispersal on the contribution of neutral and selective processes in the assembly of floral microbiomes of the yellow monkeyflower (Mimulus guttatus). We sampled floral organs from flowers in the presence and absence of pollinators within five different serpentine seeps in CA and obtained 16S amplicon data on the epiphytic bacterial communities. Consistent with strong micro-environment selection within flowers we observed significant differences in community composition across floral organs and only a small effect of geographic distance. Pollinator exposure affected the contribution of environmental selection and depended on the rate and "intimacy" of interactions with flower visitors. This study provides evidence of the importance of dispersal and within-flower heterogeneity in shaping epiphytic bacterial communities of flowers, and highlights the complex interplay between pollinator behavior, environmental selection and additional abiotic factors in shaping the epiphytic bacterial communities of flowers.

Fertilization alters protistan consumers and parasites in crop‐associated microbiomes

“…This finding is consistent with previous reports that different plant–soil compartments (e.g. leaves, roots, or flowers) typically harbour unique microbiota, though protists were not included in these studies (Gómez and Ashman, 2019; Leveau, 2019; Massoni et al ., 2020; Pascale et al ., 2020), except that a clear distinction of Cercozoa (Rhizaria) and Oomycota (Stramenopiles) was found between compartments of the model plant Arabidopsis thaliana (Sapp et al ., 2018). Our results showed that protists in sorghum‐associated microbiomes were predominated by the supergroup Rhizaria.…”

“…Plant microbiome assembly models suggest that specific microbes in the environment colonize plant surfaces, followed by additional filtering as microbial taxa are recruited into the interior of plant organs (Bulgarelli et al ., 2013). Leaf phyllosphere is an open environment, and surface colonizing protists may disperse from the surrounding environment, such as soil, neighbouring plants, insects, animals and aerosols, or migrate from other plant tissues (Gómez and Ashman, 2019), though plant endophytes were not characterized in the current study. Plant genetic traits that can mediate leaf tissue chemistry and the surface topology (Liu et al ., 2020) may also contribute to the colonization of phyllosphere protists.…”

The Plant Microbiome: From Ecology to Reductionism and Beyond

“…While selection and drift alter the abundance of existing members within a community, dispersal and diversification are how new species arise in communities. Plant-colonizing microorganisms disperse from the surrounding environment (i.e., horizontal transmission), including soil (83), neighboring plants and interacting animals (111), and the air column ( 28), although vertical transmission via seed can also occur (100,119). After initial colonization, microbial dispersal to and from plants is likely to occur.…”

Nectar bacteria stimulate pollen germination and bursting to enhance their fitness

“…More direct effects are also possible. Acinetobacter is common on many floral surfaces, including stigmas(52) and is prevalent in seed microbiomes (53), particularly following pollinator visitation. Whether Acinetobacter growth on stigmas affects pollen germination and success in fertilization will also require further study.As we have demonstrated, the presence and growth of floral Acinetobacter can significantly affect pollen physiology and may have important consequences for plants and pollinators(18,42,47,51).…”