Impact of Bacterial-Fungal Interactions on the Colonization of the Endosphere

Research on different endophyte taxa and the related scientific disciplines have largely developed separately, and comprehensive community-level studies on bacterial and fungal interactions and their importance are lacking. Here, we discuss the transmission modes of bacteria and fungi and the nature of their interactions in the endosphere at both the molecular and physiological level. Mixed-community biofilms in the endosphere may have a role in protecting endophytes against encountered stresses, such as from plant defense systems. However, transmission from static (in biofilms) to free-living (planktonic) forms may be crucial for the exploration of new habitable spaces in plants. Important features previously recognized as plant-microbe interactions or antagonism in endophyte genomes and metagenomes are proposed to have essential roles in the modulation of endophyte communities. No general consensus can be provided on the precise ecological boundaries of different types of endophyte or on the establishment of their interactions with plants.Traditionally, understanding of bacterial and fungal endophytes developed in separate research fields and both taxa have rarely been studied in one single integrated approach.Interactions between plants and individual populations of endophytes are key in most studies and, with the exception of antagonism against phytopathogens, no other interactions between members of the endophytic communities have been taken into account.The inner tissues of plants are hostile environments to most microorganisms due to competition with the host plant and with other microbes for nutrients and available space.