Bacterial dispersal and biogeography as underappreciated influences on phytobiomes

Symbiosis vs pathogenesis in plants: Reflections and perspectives

Plant-microbe partnerships constitute a complex and intricately woven network of connections that have evolved over countless centuries, involving both cooperation and antagonism. In various contexts, plants and microorganisms engage in mutually beneficial partnerships that enhance crop health and maintain balance in ecosystems. However, these associations also render plants susceptible to a range of pathogens. Understanding the fundamental molecular mechanisms governing these associations is crucial, given the notable susceptibility of plants to external environmental influences. Based on quorum sensing signals, phytohormone, and volatile organic carbon (VOC) production and others molecules, microorganisms influence plant growth, health, and defense responses. This review explores the multifaceted relationships between plants and their associated microorganisms, encompassing mutualism, commensalism, and antagonism. The molecular mechanisms of symbiotic and pathogenic interactions share similarities but lead to different outcomes. While symbiosis benefits both parties, pathogenesis harms the host. Genetic adaptations optimize these interactions, involving coevolution driving process. Environmental factors influence outcomes, emphasizing the need for understanding and manipulation of microbial communities for beneficial results. Research directions include employing multi-omics techniques, functional studies, investigating environmental factors, understanding evolutionary trajectories, and harnessing knowledge to engineer synthetic microbial consortia for sustainable agriculture and disease management.

A framework for integrating microbial dispersal modes into soil ecosystem ecology

Dispersal is a fundamental community assembly process that maintains soil microbial biodiversity across spatial and temporal scales, yet the impact of dispersal on ecosystem function is largely unpredictable. Dispersal is unique in that it contributes to both ecological and evolutionary processes and is shaped by both deterministic and stochastic forces. The ecosystem-level ramifications of dispersal outcomes are further compounded by microbial dormancy dynamics and environmental selection. Here we review the knowledge gaps and challenges that remain in defining how dispersal, environmental filtering, and microbial dormancy interact to influence the relationship between microbial community structure and function in soils. We propose the classification of microbial dispersal into three categories, through vegetative or active cells, through dormant cells, and through acellular dispersal, each with unique spatiotemporal dynamics and microbial trait associations. This conceptual framework should improve the integration of dispersal in defining soil microbial community structure-function relationships.

Horsenettle (Solanum carolinense) fruit bacterial communities are not variable across fine spatial scales

Fruit house microbial communities that are unique from the rest of the plant. While symbiotic microbial communities complete important functions for their hosts, the fruit microbiome is often understudied compared to other plant organs. Fruits are reproductive tissues that house, protect, and facilitate the dispersal of seeds, and thus they are directly tied to plant fitness. Fruit microbial communities may, therefore, also impact plant fitness. In this study, we assessed how bacterial communities associated with fruit of Solanum carolinense, a native herbaceous perennial weed, vary at fine spatial scales (<0.5 km). A majority of the studies conducted on plant microbial communities have been done at large spatial scales and have observed microbial community variation across these large spatial scales. However, both the environment and pollinators play a role in shaping plant microbial communities and likely have impacts on the plant microbiome at fine scales. We collected fruit samples from eight sampling locations, ranging from 2 to 450 m apart, and assessed the fruit bacterial communities using 16S rRNA gene amplicon sequencing. Overall, we found no differences in observed richness or microbial community composition among sampling locations. Bacterial community structure of fruits collected near one another were not more different than those that were farther apart at the scales we examined. These fine spatial scales are important to obligate out-crossing plant species such as S. carolinense because they are ecologically relevant to pollinators. Thus, our results could imply that pollinators serve to homogenize fruit bacterial communities across these smaller scales.

Seed-Transmitted Bacteria and Fungi Dominate Juvenile Plant Microbiomes

Plant microbiomes play an important role in agricultural productivity, but there is still much to learn about their provenance, diversity, and organization. In order to study the role of vertical transmission in establishing the bacterial and fungal populations of juvenile plants, we used high-throughput sequencing to survey the microbiomes of seeds, spermospheres, rhizospheres, roots, and shoots of the monocot crops maize (B73), rice (Nipponbare), switchgrass (Alamo), Brachiaria decumbens, wheat, sugarcane, barley, and sorghum; the dicot crops tomato (Heinz 1706), coffee (Geisha), common bean (G19833), cassava, soybean, pea, and sunflower; and the model plants Arabidopsis thaliana (Columbia-0) and Brachypodium distachyon (Bd21). Unsterilized seeds were planted in either sterile sand or farm soil inside hermetically sealed jars, and after as much as 60 days of growth, DNA was extracted to allow for amplicon sequence-based profiling of the bacterial and fungal populations that developed. Seeds of most plants were dominated by Proteobacteria and Ascomycetes, with all containing operational taxonomic units (OTUs) belonging to Pantoea and Enterobacter. All spermospheres also contained DNA belonging to Pseudomonas, Bacillus, and Fusarium. Despite having only seeds as a source of inoculum, all plants grown on sterile sand in sealed jars nevertheless developed rhizospheres, endospheres, and phyllospheres dominated by shared Proteobacteria and diverse fungi. Compared to sterile sand-grown seedlings, growth on soil added new microbial diversity to the plant, especially to rhizospheres; however, all 63 seed-transmitted bacterial OTUs were still present, and the most abundant bacteria (Pantoea, Enterobacter, Pseudomonas, Klebsiella, and Massilia) were the same dominant seed-transmitted microbes observed in sterile sand-grown plants. While most plant mycobiome diversity was observed to come from soil, judging by read abundance, the dominant fungi (Fusarium and Alternaria) were also vertically transmitted. Seed-transmitted fungi and bacteria appear to make up the majority of juvenile crop plant microbial populations by abundance, and based on occupancy, there seems to be a pan-angiosperm seed-transmitted core bacterial microbiome. Further study of these seed-transmitted microbes will be important to understand their role in plant growth and health, as well as their fate during the plant life cycle and may lead to innovations for agricultural inoculant development.