Importance of OsRac1 and RAI1 in signalling of nucleotide‐binding site leucine‐rich repeat protein‐mediated resistance to rice blast disease

Abstract

Summary Plants depend on Resistance (R) genes, most of which encode nucleotide‐binding site leucine‐rich repeat (NLR) proteins, for pathogen race‐specific disease resistance. However, only a few immediate downstream targets of R proteins have been characterized, and the signalling pathways for R‐protein‐induced immunity are largely unknown. In rice (Oryza sativa), NLR proteins serve as important immune receptors in the response to rice blast disease caused by the fungus Magnaporthe oryzae. We used site‐directed mutagenesis to create an autoactive form of the NLR protein PID3 that confers blast resistance and used transgenic rice to test the resulting immunity and gene expression changes. We identified OsRac1, a known GTPase, as a signalling molecule in PID3‐mediated blast resistance, implicating OsRac1 as a possible common factor downstream of rice NLR proteins. We also identified RAI1, a transcriptional activator, as a PID3 interactor required for PID3‐mediated blast resistance and showed that RAI1 expression is induced by PID3 via a process mediated by OsRac1. This study describes a new signalling pathway for NLR protein‐mediated blast resistance and shows that OsRac1 and RAI1 act together to play a critical role in this process.

Diversity, structure and function of the coiled‐coil domains of plant NLR immune receptors

“…The MLA CC domain also interacts with the positive defense regulator MYB6 in the nucleus, thus blocking the interaction between WRKY1 and MYB6 and releasing MYB6 from WRKY1‐imposed repression to enhance its DNA binding activity (Chang et al, 2013). The CC domain of rice PID3 interacts with the TF RAC IMMUNITY1 (RAI1), a positive regulator of PID3‐mediated resistance to M. oryzae (Zhou et al, 2019). Similarly, the Rx CC domain interacts with the Golden2‐like TF NbGlk1, lowering its DNA binding affinity at least in vitro , and blocking the assembly of NbGlk1 on DNA in vivo unless activated by PVX infection (Townsend et al, 2018).…”

Regulation and Functions of ROP GTPases in Plant–Microbe Interactions

“…In ETI, RAI1 has recently been reported to be a signaling component in another NLR protein-mediated resistance pathway in rice. In this pathway, the NLR protein PID3 requires OsRAC1 to induce RAI1 expression to confer rice blast resistance [53]. Together with Pit and Pia, PID3 is yet another NLR protein that triggers ETI-mediated disease resistance in which OsRAC1 is involved.…”

Identification of rice (Oryza sativa L.) genes involved in sheath blight resistance via a genome‐wide association study

“…In Arabidopsis thaliana , the RLCK protein PBS1 regulates resistance against Pseudomonas syringae and recognition by the P. syringae AvrPphB effector protease (Shao et al, 2003 ). Plant genomes encode several hundred NLR proteins involved in defence responses (Marone et al, 2013 ), some of which occur in clusters at specific loci following gene duplication and amplification events (Liu et al, 2014 ; Zhou et al, 2019 ). Furthermore, based on physical or genetic mapping it is apparent that many NLR genes co‐localize with resistance loci (McHale et al, 2006 ).…”