Plasma Membrane Microdomains Are Essential for Rac1-RbohB/H-Mediated Immunity in Rice

Abstract

Numerous plant defense-related proteins are thought to congregate in plasma membrane microdomains, which consist mainly of sphingolipids and sterols. However, the extent to which microdomains contribute to defense responses in plants is unclear. To elucidate the relationship between microdomains and innate immunity in rice (Oryza sativa), we established lines in which the levels of sphingolipids containing 2-hydroxy fatty acids were decreased by knocking down two genes encoding fatty acid 2-hydroxylases (FAH1 and FAH2) and demonstrated that microdomains were less abundant in these lines. By testing these lines in a pathogen infection assay, we revealed that microdomains play an important role in the resistance to rice blast fungus infection. To illuminate the mechanism by which microdomains regulate immunity, we evaluated changes in protein composition, revealing that microdomains are required for the dynamics of the Rac/ROP small GTPase Rac1 and respiratory burst oxidase homologs (Rbohs) in response to chitin elicitor. Furthermore, FAHs are essential for the production of reactive oxygen species (ROS) after chitin treatment. Together with the observation that RbohB, a defense-related NADPH oxidase that interacts with Rac1, is localized in microdomains, our data indicate that microdomains are required for chitin-induced immunity through ROS signaling mediated by the Rac1-RbohB pathway.

The Monocot-Specific Receptor-like Kinase SDS2 Controls Cell Death and Immunity in Rice

“…OsRbohB (LOC_Os01g25820) is the major NADPH oxidase responsible for ROS production on the plasma membrane in rice (Nagano et al, 2016; Wong et al, 2007). OsRbohB is also the orthologue of Arabidopsis RbohD, which is regulated by BIK1, which belongs to the same clade as OsRLCK118/176 (Shiu et al, 2004).…”

TMD1 domain and CRAC motif determine the association and disassociation of MxIRT1 with detergent‐resistant membranes

“…The Rho‐related C3 botulinum toxin substrate in Oryza sativa (OsRac1) and the receptor for activated C kinase 1 (RACK1A) relocate to microdomains after chitin elicitor treatment, suggesting that OsRac1‐mediated innate immunity requires microdomains in the PM . These microdomains are also required for chitin‐induced immunity through respiratory oxygen species (ROS) signaling mediated by the Rac1‐RbohB pathway . Additionally, transporters have been found in plant microdomains, including members of the ABC transporter family, several amino acid transporters and sucrose transporters .…”

ROP GTPases Structure-Function and Signaling Pathways

“…ROPs activate RBOH-type NADPH oxidases during immune responses (Wong et al, 2007;Nagano et al, 2016). The SCN1/RhoGDI1-dependent and RHD2/AtRBOHCdependent ROS accumulation at RH formation sites strongly suggest that ROP2/4 activates RBOHC during RH formation and growth (Carol et al, 2005).…”

“…pat4 RHs are shorter, and the multiple RH phenotype of the scn1/rhogdi1 mutant is suppressed in the pat4 background. Furthermore, ROPs activate rice RBOHB/H by recruiting them into lipid microdomains (Nagano et al, 2016). At the future RH initiation sites, ROP2/6 colocalize with PIP 4 phosphate 5 kinase 3, Dynamin Related Protein1A (DRP1A) and DRP2B, and the AGCVIII kinase D6 Protein Kinase (D6PK) in sterol-enriched domains .…”

“…In the presence of chitin, OsCERK1 phosphorylates and activates OsRACGEF. In turn, OsRAC1 activation activates lignin biosynthesis by activating Cinnamoyl CoA Reductase and ROS production by the activation of NADPH oxidase (Wong et al, 2007;Akamatsu et al, 2013;Nagano et al, 2016).…”