The role of microbial seed endophytes in agriculture: mechanisms and applications

Plants have microbial companions inhabiting a hidden world within their tissues that play relevant roles in their environmental fitness. Some of these beneficial microorganisms can colonize seeds by exerting a functional echo in future generations. In this study, we review the most recent advances in microbial endophytes residing in seeds and their ecological functions, including the reproductive stage, from germination to adulthood. Similar to free-living plant growth-promoting microorganisms, microbial endophytes, whether bacteria or fungi, exhibit similar direct (e.g., facilitation of resources and regulation of phytohormones) and indirect (e.g., antibiosis and induced systemic resistance) action mechanisms, which are also analyzed. Finally, some agro-biotechnological applications of microbial endophytes and their advantages of being inherited through seeds are discussed, such as facilitating their field application and ensuring that their beneficial actions increase crop health and sustainable production.