Cinnamoyl-CoA reductase, a key enzyme in lignin biosynthesis, is an effector of small GTPase Rac in defense signaling in rice

Abstract

OsRac1, one of the Rac͞Rop family of small GTPases, plays important roles in defense responses, including a role in the production of reactive oxygen species mediated by NADPH oxidase. We have identified an effector of OsRac1, namely rice (Oryza sativa) cinnamoyl-CoA reductase 1 (OsCCR1), an enzyme involved in lignin biosynthesis. Lignin, which is polymerized through peroxidase activity by using H 2O2 in the cell wall, is an important factor in plant defense responses, because it presents an undegradable mechanical barrier to most pathogens. Expression of OsCCR1 was induced by a sphingolipid elicitor, suggesting that OsCCR1 participates in defense signaling. In in vitro interaction and two-hybrid experiments, OsRac1 was shown to bind OsCCR1 in a GTP-dependent manner. Moreover, the interaction of OsCCR1 with OsRac1 led to the enzymatic activation of OsCCR1 in vitro. Transgenic cell cultures expressing the constitutively active OsRac1 accumulated lignin through enhanced CCR activity and increased reactive oxygen species production. Thus, it is likely that OsRac1 controls lignin synthesis through regulation of both NADPH oxidase and OsCCR1 activities during defense responses in rice.defense response ͉ G protein ͉ monolignol

Chitin and chitin-related compounds in plant–fungal interactions

“…OsRac1 is one of the seven rice Rac/Rop GTPases and plays essential roles in chitin-induced immune responses. However, it represents a part not only in the expression of immune-related genes but also ROS production and lignification (Kawasaki et al 1999, 2006; Ono et al 2001; Wong et al 2007). OsRacGEF1, the GEF for OsRac1, is a part of the plant-specific ROP-nucleotide exchanger (PRONE)-type GEF family.…”

“…These reactions include the following: ion flux variations, cytoplasmic acidification, membrane depolarisation and protein phosphorylation (Felix et al 1993, 1998), chitinase and glucanase activation (Roby et al 1987; Tayeh et al 2015), lignification (Kawasaki et al 2006; Ali et al 2014), generation of reactive oxygen species (ROS) (Kuchitsu et al 1995), biosynthesis of jasmonic acid (JA) (Nojiri et al 1996), and phytoalexins (Ren and West 1992; Yamada et al 1993), and the expression of early responsive and defence-related genes (Minami et al 1996; Libault et al 2007). Moreover, chitosan induces proteinase inhibitors (Walker-Simmons and Ryan 1984), phytoalexin biosynthesis (Hadwiger and Beckman 1980) and callose formation (Köhle et al 1985) in dicot species.…”

Rice RING protein OsBBI1 with E3 ligase activity confers broad-spectrum resistance against Magnaporthe oryzae by modifying the cell wall defence

“…Two R genes, Pi9 and Pi21, confer broad-spectrum resistance against multiple races of M. oryzae [9,10]. Rac GTPasemediated events (e.g., generation of ROS), activation of MAP kinase, and other key components, such as RAR1, SGT1, Hsp90, and WRKY45, play important roles in regulating the immune response against M. oryzae [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Endogenous SA is involved in defence against M. oryzae [25].…”

A RHOse by any other name: a comparative analysis of animal and plant Rho GTPases

“…In rice, a pathway leading from heterotrimeric G protein via OsRac1 to NADPH oxidase confers disease resistance towards pathogens such as rice blast fungus [96][97][98]. Although the precise mechanism of this pathway has not yet been resolved, Kawasaki et al [99] mention as unpublished results that ROP regulates Rboh activity through direct interaction. It will be interesting to see whether this interaction is similar to the interaction between Rac and gp91 phox in mammalian cells.…”

“…Recently, rice cinnamoyl-CoA reductase1 (OsCCR1), an enzyme involved in lignin biosynthesis, was shown to interact with OsRac1 in a GTP-dependent manner [99]. Interaction with OsRac1 induced the enzymatic activity of OsCCR1 in vitro.…”