Plant-microbe symbioses: A continuum from commensalism to parasitism

Photosynthetic organisms establish symbioses with a wide range of microorganisms. This review examines the diversity of symbiotic interactions, and proposes that there is a continuum from commensalism to mutualism to pathogenesis/parasitism in plant-microbe associations. The advantage of considering commensalism, mutualism, and pathogenesis/parasitism as a continuum rather than as discrete relationships between hosts and microbes, as they have been considered in the past, is that it will motivate us to focus more on common molecular mechanisms.