Plant responses to plant growth promoting bacteria: Insights from proteomics

Abstract

Plant growth-promoting bacteria (PGPB) modes of action are highly complex and the totality of mechanisms they are able to use for plant growth or stress amelioration remains unknown. Although there are well documented bacterial mechanisms (nitrogen fixation, phytohormones production, etc.), there are many plant responses to PGPB at the molecular level that are still clueless. Omics sciences offer large-scale and untargeted approaches to study them. Concretely, proteomics may unravel key events through the observation of protein expression dynamics in plants after PGPB inoculation. We summarized and discussed the existing literature about proteomic studies on plant response to PGPB, with special emphasis in crops. We also developed several meta-analyses to merge results of independent studies and detect potential key changes in plant proteome, through most common differentially expressed proteins. We found that effects of PGPB in plant growth were highly related to overexpression of ROS-reduction proteins, promotion of the photosynthetic machinery, transcription (especially histone-mediated), cell architecture, energy metabolism and nutrient uptake. On the other hand, PGPB inoculation of plants under different stresses generally induced the expression of ROS-related proteins, HSP for protein processing and proteasomes. We also observed an overlap between pathways, acting as general and shared responses to multiple biotic and abiotic stresses. Finally, we brought to the fore gaps of knowledge in the field for further research.