AtRAC7/ROP9 Small GTPase Regulates A. thaliana Immune Systems in Response to B. cinerea Infection

Botrytis cinerea is a necrotrophic fungus that can cause gray mold in over 1400 plant species. Once it is detected by Arabidopsis thaliana, several defense responses are activated against this fungus. The proper activation of these defenses determines plant susceptibility or resistance. It has been proposed that the RAC/ROP small GTPases might serve as a molecular link in this process. In this study, we investigate the potential role of the Arabidopsis RAC7 gene during infection with B. cinerea. For that, we evaluated A. thaliana RAC7-OX lines, characterized by the overexpression of the RAC7 gene. Our results reveal that these RAC7-OX lines displayed increased susceptibility to B. cinerea infection, with enhanced fungal colonization and earlier lesion development. Additionally, they exhibited heightened sensitivity to bacterial infections caused by Pseudomonas syringae and Pectobacterium brasiliense. By characterizing plant canonical defense mechanisms and performing transcriptomic profiling, we determined that RAC7-OX lines impaired the plant transcriptomic response before and during B. cinerea infection. Global pathway analysis of differentially expressed genes suggested that RAC7 influences pathogen perception, cell wall homeostasis, signal transduction, and biosynthesis and response to hormones and antimicrobial compounds through actin filament modulation. Herein, we pointed out, for first time, the negative role of RAC7 small GTPase during A. thaliana–B. cinerea interaction.