Microbial endophytes: evolution, diversity, community functions, and regulation

Abstract Microbial endophytes are important contributors to the ecological success of plants. We review these interactions as mutualisms and present discussions on our current state of understanding regarding components of these interactions. We present evidence of endophyte evolution overall and at the cellular level, while heavily emphasizing endophytes of the fungal family Clavicipitaceae as models for endophytes—at least as models of endophytic fungi. However, some discussion is made of other fungal groups along with bacteria. This is particularly important because in nature plants are colonized by communities of endophytic microbes, not single species of endophytes. We also include life cycle variations and modes of plant colonization both within and among several plant organs. The resulting plants and endophytic microbial communities are successful in terms of their having varied geographic patterns and distributions, and with respect to how their endophytic species are organized and regulated within them. Since endophytic organisms and their hosts are evolutionarily distant, we presented some information on how the two partners within the symbiosis might signal one another, which may be related to using quorum sensing and inhibitions. Since very little about quorum sensing is known in fungi, we use bacteria as models for how such mechanisms for regulation and control of important biochemical pathways and developmental processes that might occur in planta partnerships. Continued research along these lines may substantiate this hypothesis and may develop into other approaches for mycotoxins produced by endophytes.