RAVL1 Activates Brassinosteroids and Ethylene Signaling to Modulate Response to Sheath Blight Disease in Rice

Abstract

Rhizoctonia solani causes sheath blight disease in rice; however, the defense mechanism of rice plants against R. solani remains elusive. To analyze the roles of brassinosteroid (BR) and ethylene signaling on rice defense to R. solani, wild-type (WT) rice and several mutants and overexpressing (OX) lines were inoculated with R. solani. Mutants d61-1 and d2 were less susceptible to sheath blight disease, bri1-D was more susceptible, and ravl1 and d61-1/EIL1 Ri5 were similarly susceptible compared with WT. The double mutant ravl1/d61-1 was phenotypically similar to the ravl1 mutant. Transcriptome analysis, chromatin immunoprecipitation assay, electrophoretic mobility shift assay, and transient assays indicted that RAVL1 might directly activate Ethylene insensitive 3-like 1 (EIL1), a master regulator of ethylene signaling. Mutants ers1 and d61-1/RAVL1 OX were resistant to sheath blight disease, whereas EIL1 RNAi mutants and RAVL1 OX were more susceptible than WT. BRI1 and D2 expression in EIL1 Ri5/RAVL1 OX and EIL1 expression in d61-1/RAVL1 OX indicated that RAVL1 activates BRI1/D2 and EIL1, respectively, independent of BR and ethylene signaling. Our analyses provide information on how BR and ethylene signaling regulate sheath blight disease and on the regulatory function of RAVL1 in rice sheath blight disease.

Overexpression of Loose Plant Architecture 1 increases planting density and resistance to sheath blight disease via activation of PIN‐FORMED 1a in rice

“…Further examination indicated that expression of PBZ1 and PR1b, two pathogen resistant genes were more highly induced in LPA1 OXs than in WT after inoculation of R. solani AG1-1 (Figure 1i,j). Our earlier work demonstrated that hormonal signals play key roles in rice resistance to SBD (Yuan et al, 2018). In addition, LPA1 positively controls the expressions of the auxin efflux carrier gene PIN-FORMED 1a (PIN1a) in the lamina joint (Liu et al, 2016).…”

Transcriptome analysis of rice leaves in response to Rhizoctonia solani infection

“…OsWRKY53 was previously reported to positively regulate BR signaling downstream of the BR receptor OsBRI1 (30). Our previous study showed that BR signaling negatively regulates the defense of rice to ShB (12), implying that OsWRKY53 might activate BR signaling to suppress the ability of rice to defend against ShB. A few IDD family genes were changed, including OsIDD14/LPA1, in the RNA-Seq data.…”

“…The Mapman analysis using the DEGs revealed that phytohormones, particularly the auxin, BR, abscisic acid (ABA), and jasmonic acid (JA)-related genes, changed significantly. Our previous study identified that BR signaling negatively regulates rice defense to ShB (12), and exogenously treated auxin promotes rice defense to ShB, as well as having identified that the auxin polar transporter OsPIN1a positively regulates the defense of rice to ShB (40). JA regulates plant defense against necrotrophic fungi (41), and the JAZ family proteins are the key regulator of JA signaling.…”

“…Dongjin and Longjing 11), OsWRKY53 overexpression plants, and Oswrky53 and Osakt1 mutants were grown in a greenhouse at Shenyang Agriculture University. One-month-old plants were used for R. solani inoculation using the method described previously (12).…”

“…Our previous research showed that brassinosteroids (BRs) negatively regulate, while ethylene enhances the resistance to ShB. The BR signaling transcription factor RAVL1 activates the key BR and ethylene signaling pathways to modulate the rice defense to ShB (12). OsWRKY4, OsWRKY13, OsWRKY30, and OsWRKY80 have been reported to positively regulate the resistance to ShB (13)(14)(15)(16), and more recently, we identified that sugar will eventually be exported via transporter 11 (SWEET11), which negatively regulates the rice resistance to ShB (17).…”