Rice WRKY4 acts as a transcriptional activator mediating defense responses toward Rhizoctonia solani, the causing agent of rice sheath blight

Abstract

WRKY transcription factors have been implicated in the regulation of transcriptional reprogramming associated with various plant processes but most notably with plant defense responses to pathogens. Here we demonstrate that expression of rice WRKY4 gene (OsWRKY4) was rapidly and strongly induced upon infection of Rhizoctonia solani, the causing agent of rice sheath blight, and exogenous jasmonic acid (JA) and ethylene (ET). OsWRKY4 is localized to the nucleus of plant cells and possesses transcriptional activation ability. Modulation of OsWRKY4 transcript levels by constitutive overexpression increases resistance to the necrotrophic sheath blight fungus, concomitant with elevated expression of JA- and ET-responsive pathogenesis-related (PR) genes such as PR1a, PR1b, PR5 and PR10/PBZ1. Suppression by RNA interference (RNAi), on the other hand, compromises resistance to the fungal pathogen. Yeast one-hybrid assay and transient expression in tobacco cells reveal that OsWRKY4 specifically binds to the promoter regions of PR1b and PR5 which contain W-box (TTGAC[C/T]), or W-box like (TGAC[C/T]) cis-elements. In conclusion, we propose that OsWRKY4 functions as an important positive regulator that is implicated in the defense responses to rice sheath blight via JA/ET-dependent signal pathway.

OsWRKY80-OsWRKY4 Module as a Positive Regulatory Circuit in Rice Resistance Against Rhizoctonia solani

“…To determine if OsWRKY80 has transcriptional activation activity, we fused the full-length OsWRKY80 in frame to the GAL4 DNA binding domain in the pGBKT7 vector and transformed into yeast strain AH109. Empty vector pBD and pBD-WRKY4 (Wang et al 2015) were used as negative and positive control, respectively. The results showed that cells transformed with pBD-WRKY80 grew well on synthetic SD-Trp-Ade-His selection media (Fig.…”

“…To date, at least 13 Oryza sativa WRKY ( OsWRKY ) genes are known to positively regulate rice resistance against pathogens, such as Magnaporthe oryzae , Rhizoctonia solani and Xanthomonas oryzae pv oryzae ( Xoo ) (Cheng et al 2015; Wang et al 2015; Choi et al 2015; Hwang et al 2016). For instance, OsWRKY13 activates SA-dependent defense response whereas suppresses JA-dependent response, in mediating rice defense response to bacterial blight and fungal blast pathogens (Qiu et al 2007).…”

“…Among those characterized OsWRKY genes, at least 12 and 10 genes have been shown to function as either positive or negative regulators in rice resistance against M. oryzae and Xoo , respectively. However, only 2 OsWRKY genes ( OsWRKY30 and OsWRKY4 ) have been shown to mediate the defense responses against R. solani (Peng et al 2012; Wang et al 2015). Additionally, rice sheath blight is a necrotrophic disease (Zhao et al 2008).…”

“…To elucidate the regulatory roles of rice WRKY factors in defense response to the sheath blight fungus, we have analyzed the expression profiles of rice WRKY family under R. solani infection and methyl jasmonate (MeJA) treatment. We have identified several pathogen- and JA-inducible WRKY genes, including OsWRKY30 and OsWRKY4 , which are positive regulators in rice resistance to R. solani (Peng et al 2012; Wang et al 2015). In this report, we investigate the expression pattern of OsWRKY80 gene in response to exogenous defense-related phytohormones JA, ET and SA and R. solani challenge.…”

OsWRKY51, a rice transcription factor, functions as a positive regulator in defense response against Xanthomonas oryzae pv. oryzae

“…This gene is also associated with the activation of several genes, including jasmonic acid (JA) biosynthesis genes and pathogenesisrelated genes (Peng et al 2012). A recent study shows that OsWRKY4, in Group I, functions as a transcriptional activator of genes important in the defense response to R. solani (Wang et al 2015). More recently it is reported that OsWRKY6 functions as a positive regulator in defense response (Hwang et al 2011;Choi et al 2015).…”