Abstract
In plants, perception of pathogen-associated molecular patterns (PAMPs) triggers innate immune responses that contribute to disease resistance. Previously, we showed that the small GTPase OsRac1, belonging to the Rac/Rop GTPase family, is a key regulator in rice defense signaling. However, the spatiotemporal dynamics of OsRac1 activation during the defense response is unknown. Here we report the development of an intracellular fluorescence resonance energy transfer (FRET) biosensor termed Raichu-OsRac1 that facilitates the in vivo monitoring of OsRac1 activation by elicitors. We showed that N-acetylchitooligosaccharide elicitor, a PAMP derived from the rice blast fungus, induced OsRac1 activation on the plasma membrane of rice protoplasts rapidly after treatment using Raichu-OsRac1. Moreover, we identified a guanine nucleotide exchange factor (GEF) that interact with OsRac1 by yeast two-hybrid assay. We confirmed that this GEF can activate OsRac1. Our results also indicated that the GEF interacts with a receptor like kinase. These data suggest that activation of OsRac1 by PAMP occurs at an early step in rice innate immunity.
