The diversity and distribution of endophytes across biomes, plant phylogeny, and host tissues--how far have we come and where do we go from here?

The interiors of plants are colonized by diverse microorganisms that are referred to as endophytes. Endophytes have received much attention over the past few decades, yet many questions remain unanswered regarding patterns in their biodiversity at local to global scales. To characterize research effort to date, we synthesized results from [~]600 published studies. Our survey revealed a global research interest and highlighted several gaps in knowledge. For instance, of the seventeen biomes encompassed by our survey, seven were understudied and together composed only 7% of the studies that we considered. We found that fungal endophyte diversity has been characterized in at least one host from 30% of embryophyte families, while bacterial endophytes have been surveyed in hosts from only 10.5% of families. We complimented our survey with a vote counting procedure to determine endophyte richness patterns among plant tissue types. We found that variation in endophyte assemblages in above-ground tissues varied with host growth habit. Stems were the richest tissue in woody plants, whereas roots were the richest tissue in graminoids. For forbs, we found no consistent differences in relative tissue richness among studies. We propose future directions to fill the gaps in knowledge we uncovered and inspire further research. Originality-Significance StatementMuch remains to be learned regarding the biodiversity and distribution of the microbes that colonize the interiors of plants. Here, we surveyed approximately 600 publications to characterize gaps in knowledge and provide a roadmap for future research. We compared biomes, plant families, and geographical regions in terms of the research interest that they have garnered. Additionally, we synthesized published results and report that variation in endophyte richness among plant tissue types is a function of host growth habit. Stems were the richest tissue in woody plants, whereas roots were the richest tissue in graminoids. We hope to inspire research to fill the gaps in knowledge that we uncovered.