Proteomic studies of plant–bacterial interactions

Plants and bacteria can interact with one another in a variety of different ways. The interaction may be beneficial, harmful or neutral for the plant, and sometimes the impact of a bacterium may vary as the soil conditions change. While a number of different soil bacteria are phytopathogenic, the majority of the more agronomically important plant disease-causing soil microorganisms are fungi. On the other hand, plant growth-promoting bacteria are typically of three general types: those that form a symbiotic relationship with the plant, those that are endophytic and colonize the inner tissues of the plant, and those of soil bacteria, which have competitive abilities to colonize efficiently the rhizosphere and the surface of plant roots.While there have been significant advances in elucidating the mechanistic details of plant–bacterial interactions in recent years, many fundamental questions about these processes remain. Unfortunately, studies that focus on only a single biochemical pathway or mechanism often miss the multiplicity of effects that plants and bacteria have on one another, motivating the employment of broader proteome-wide approaches. On the other hand, using proteomics technology including high-resolution two-dimensional gel electrophoresis (2-DE) and high-sensitivity mass spectrometry (MS), it is possible to gain greater insight into the detailed impact that plants and soil bacteria have on one another.In this regard, of all of the proteomic studies of plant–bacterial interactions, the symbiotic interaction between nitrogen-fixing bacteria and legumes has been studied in the greatest detail. Studies of the proteome of plant–pathogen interactions have also received considerable attention. However, there are currently very few proteomic studies of endophytic and rhizosphere associated plant growth promoting bacteria.Here, some fundamental proteomic tools are introduced and the applications of one of these approaches (i.e., 2-DE coupled to MS) to the study of plant–bacterial interactions are discussed. This review specifically addresses the questions: what are the impacts of plants on the bacterial proteomes, and vice versa?