The Fungal Pathogen Magnaporthe Oryzae Suppresses Innate Immunity By Modulating A Host Potassium Channel

Rice blast,caused by Magnaporthe oryzae,is one of the most devastating fungal diseases in rice and may result in great yield loss when there is an outbreak.It has been proved that the most ecomonical and effective way to fight against rice blast is taking advantage of blast resistance genes(R genes).However,due to the complicacy and virability of M.oryzae isolates in natural environment,a blast R gene will be quickly defeated within 2~3 years.Thus,studies on the mechamisms about how blast R genes work and how rice interacts with M.oryzae will provide theoretical basis for better using and arrangement of blast R genes.Piz-t is a rice blast R gene that is localized on chromosome 6 and is allelic to Pi2,Pi9,Pi50 andPigmR.The corresponding avrirulence gene of Piz-t in M.oryzae,AvrPiz-t,was also cloned.However,no direct interaction between Piz-t and AvrPiz-t has been identified.To figure out the recognition mechanism,we previously screened a rice cDNA library with AvrPiz-t as the bait using yeast two-hybrid(Y2H)method.We obtained 12 AvrPiz-t interaction proteins,named APIP1-12,among which APIP7 is the potassium channel protein OsAKT1.In this work,the role of OsAKT1 in the interaction of rice and M.oryzae was further studied.OsAKT1 is the orthologue of Arabidopsis AKT1 and plays important roles in K~+uptake.The channelactivity of OsAKT1 is positively regulated by upstream OsCBL1-OsCIPK23 module.In this work,we confirmed that AvrPiz-t could interact with the C-terminal intracellular domain of OsAKT1 both in vitro and in vivo.OsAKT1-mediated K~+currents were severely inhibited in HEK293 cells when Avrpiz-t was co-expressed with OsAKT1.The AvrPiz-t transgenic plants showed weakened K~+uptake under lower K~+level.Phenotypic analysis of osakt1 mutant and OsAKT1 RNAi plants incidated that OsAKT1 is a positive regulator of blast resistance.Furthermore,we found that AvrPiz-t was capable of competing with OsCIPK23 to bind OsAKT1,which might block the activation of OsAKT1.Due to this effect,we inoculated oscipk23 mutant and OsCIPK23 CRISPR-Cas9 gene-editing plants with M.oryzae.The results showed that OsCIPK23 is also required for K~+absoption and blast resistance.Considering the posivte roles of OsAKT1 and OsCIPK23 in rice against M.oryzae,we determined that higher K~+level increased rice blast resistance by using the hydroponic method.Based on the results obtained in this study and those from previous publications,we proposed a working model of AvrPiz-t.