Abstract
Plant-microbe interactions in floral organs greatly affect host survival and reproduction through various mechanisms, including vertical transmission of microbes from flowers to seeds and the effects on pollinator attraction. The influences of microbial dispersal by pollinators on the floral microbiome have been extensively explored; however, recent meta-barcoding studies have defined new factors that modulate the microbiome. The floral organs -- pistil, stamen, and petals -- provide diverse habitats for floral microbes. Various floral characteristics, such as UV reflection by petal surfaces, affect floral microbes by changing the environment. Host-plant immunity places strong selective pressure on microbes. The interactions between host plants and various organisms, including pollinators and nectar robbers, affect the floral microbiome by facilitating microbial dispersal and triggering inducible defensive responses of the host plant. The plant environment and other plants growing near the host plant affect microbial migration to host flowers through mechanisms mediated by wind, rain, and flower visitors, which may result in the context-dependency of the floral microbiome. Complex interactions among such factors may determine the flower microbiome. However, there remains a lack of clarity concerning how such factors influence the microbiome, as well as the effects of such microbial changes on host-plant growth and fitness. Experimental studies are needed to elucidate fully plant-microbe interactions on flowers.
