Mechanism Of The SWEET Regulating Rice Resistance To Sheath Blight

Pathogen-host interaction is a complicated process,pathogens mainly infect host plants to acquire nutrients,especially sugars.Rhizoctonia solani,the causative agent of sheath blight disease(Sh B),is a major pathogen of rice.However,it is not known how this pathogen obtains sugar from rice.In this study,the mechanism of Sugars Will Eventually be Exported Transporter(SWEET)in rice sheath blight resistance was studied.The main findings are as follows:1.The rice sugar transporter Os SWEET11 is involved in the pathogenesis of sheath blight disease.q RT-PCR and β-D-glucuronidase expression analyses showed that R.solani infection significantly enhanced Os SWEET11 expression in leaves amongst the clade III SWEET members.The analyses of transgenic plants revealed that ossweet11 mutants were less susceptible,whereas plants over-expressing Os SWEET11 were more susceptible,to sheath blight compared with wild-type controls,but the yield of ossweet11 mutants and overexpressors was reduced.The yeast one-hybrid assay showed that Os WRKY36 was combined with Os SWEET11.Therfore,the OSWRKY36 overexpressor was constructed.The resistance analysis showed that Os WRKY36 negatively regulated the resistance to sheath blight.2.Split-ubiquitin yeast two-hybrid,bimolecular fluorescence complementation and coimmunoprecipitation assays showed that the mutated Os SWEET11 interacted with the normal Os SWEET11.In addition,expression of conserved residue mutated At SWEET1 inhibited normal At SWEET1 activity.To analyse whether the inhibition of Os SWEET11 function in mesophyll cells is related to defence against sheath blight disease,mutated Os SWEET11 was expressed under the control of the Rubisco promoter,which is specific for green tissues.The resistance of transgenic plants to sheath blight disease was improved and the yield production was not obviously affected.Overall,these results suggest that R.solani might acquire sugar from rice leaves by the activation of Os SWEET11 expression.The plants can be protected from infection by manipulation of the expression of Os SWEET11 without affecting the crop yield.3.Os SWEET11 plays a key role in the interaction between rice and sheath blight.Therefore,this study verified whether other members of the SWEET family in rice were involved in the interaction with R.solani.The results of RT-PCR and q RT-PCR showed that the infection of R.solani not only significantly induced Os SWEET11,but also increased the expression of Os SWEET2 a.The previous transcriptome analysis also showed that infection with R.solani significantly induced the expression of Os SWEET2 a.The ossweet2 a genome-editing mutants were less susceptible to sheath blight.Further yeast-one hybrid,Ch IP-q PCR,and transient assays demonstrated that Os WRKY53 binds to the Os SWEET2 a promoter to activate its expression.Os WRKY53 is a key brassinosteroid(BR)signaling transcription factor.Similar to the BR receptor gene osbri1 and biosynthetic gene osd2 mutants,the oswrky53 mutant and overexpressor were less and more susceptible to Sh B compared to wild-type,respectively.4.Inoculation with R.solani induced expression of Os BRI1,Os D2,and Os WRKY53,but reduced Os MPK6(a BR-signaling regulator)activity,and Os MPK6 mutant osdsg1 negatively regulates rice resistance to sheath blight.Also,Os MPK6 is known to phosphorylate Os WRKY53 to enhance its transcription activation activity.Transient assay results indicated that co-expression of Os MPK6 and Os WRKY53 enhanced the trans-activation activity of Os SWEET2 a.Furthermore,expression of Os WRKY53 SD(the active phosphorylated forms of Os WRKY53)but not Os WRKY53 SA(the inactive phosphorylated forms of Os WRKY53),enhanced Os WRKY53-mediated activation of Os SWEET2 a.Taken together,the analyses showed that R.solani infection may activate BR signaling to induce the expression of Os SWEET2 a via Os WRKY53 through negative regulation of sheath blight resistance in rice.To sum up,it’s demonstrated that Os WRKY36-Os SWEET11 signaling pathway negatively regulates sheath blight,and the interaction between mutant Os SWEET11 and wild-type Os SWEET11 in mesophyll cells can improve the resistance of transgenic rice without affecting the yield.Subsequently,it was found that BR signal negatively regulated rice sheath blight through Os WRKY53 activating susceptibility gene Os SWEET2 a,and inoculation of R.solani inhibited the phosphorylation level of Os MPK6.The co-expression of Os MPK6 and Os WRKY53 enhanced the transcriptional activation activity of Os WRKY53 to Os SWEET2 a.In addition,osdsg1 negatively regulates rice resistance to sheath blight,which indicates that BR-mediated Os WRKY53 and Os MPK6 might balance the expression of Os SWEET2 a,thus negatively regulating rice resistance to sheath blight.This study expand the molecular mechanism of rice resistance to sheath blight and provide useful information for the defense function of rice.