Further Defining Soterobionts as Microbes in Plant Disease Suppression and Their Potential Origins

Abstract

Plants have co-evolved with microorganisms for millions of years, resulting in a variety of interactions. Recently, the term soterobiont (plural: soterobionts) has been proposed to define microorganisms that prevent disease in plants. This review further explores what defines soterobionts and the potential origins of their disease-suppressive abilities. We discuss their functional traits and examine both vertical inheritance of disease-suppressive abilities and horizontal gene transfer (HGT) via mobile genetic elements (MGEs) as mechanisms for the transmission of these abilities, since MGEs play a key role in microbial evolution and functional adaptation. Based on current knowledge, we propose that soterobionts do not always act in a defined group of species. Moreover, they likely require rhizosphere competence traits tailored to their host(s), in addition to possessing one or more antagonistic mechanisms targeting specific pathogens. However, as these traits are not exclusive to soterobionts, their distinguishing feature may lie in their ability to specialize or combine multiple functions, enabling them to thrive and perform effectively in specific ecological contexts. The notable prevalence of certain genera among soterobionts is unlikely to be coincidental, as functional analyses highlight their significant role in soterobiont functionality. Possible hypotheses to explain this include a shared evolutionary history, potentially reflecting evolutionary relatedness within genera (whether soterobiont or pathogenic), or horizontal gene transfer involving MGEs. It would be beneficial for research on soterobionts to shift from focusing on individual cases of disease suppression to a larger-scale, systemic approach. A deeper understanding of soterobionts could offer valuable insights for future research, ultimately contributing to the development of biocontrol agents that support more sustainable agricultural practices.