The Molecular Mechanism Of MiR160a-ARF8 Module Coordinates Rice Resistance And Development

Rice is one of the most important crops and supports over half of the people worldwide.However,rice production is threatened by various pathogens and insects.Breeding resistant rice cultivars is the most useful and effective methods to improve rice production with reduced use of pesticides and reduced harm to environment.However,pathogens population evolves fast and counteracts with the resistance mediated by R protein.This greatly shortens the durable years of rice resistance cultivars.As a result,it’s emergency and meaningful to look for new gene resources that mediate rice durable and broad-spectrum resistance.In our previous work,we identified a series of miRNAs that respond to M.oryzae using a rice blast susceptible accession Lijiang Xintuan Heigu and the resistant line IRBLKm-Ts.Several miRNAs regulate rice resistance positively or negatively.In this study,we focused on miR160 a that accumulates in the resistance lines upon M.oryzae infection.From our studies,we summarized four conclusions:1.miR160 a positively regulates rice resistance to multiple disease.Our data showed that overexpressing miR160a(OX160a)enhances basal immune responses and resistance to M.oryzae,Xoo and R.solani,whereas blocking the function of miR160a (MIM160)suppresses basal immune response and compromises rice resistance.2.ARF8 is one of target gene of miR160 a and negatively regulates rice resistance to multiple disease.Our data demonstrated that miR160 a targets ARF8 and suppresses its expression to promote rice immunity.Overexpression of ARF8(OXARF8)showed phenotypes similar to MIM160 including suppressed basal immune responses and enhanced susceptibility to the M.oryzae and R.solani;whereas,mutation of ARF8 (arf8)mimics the phenotypes of OX160 a showing enhanced basal immune responses and improved resistance against M.oryzae and Xoo.3.ARF8 directly regulates WRKY45 expression to direct rice resistance to M.oryzae. Moreover,we demonstrated that miR160a-ARF8 module boosts rice blast resistance via Os WRKY45,a positive regulator of rice blast disease resistance.ARF8 encodes a transcription repressor that directly binds to the WRKY45 promoter and suppresses its activity,thus down-regulating WRKY45 expression.The expression of WRKY45 is enhanced in arf8 while mutation of WRKY45 in arf8 background abolishes the blast resistance conferred by arf8,indicating the prominent role of WRKY45 in arf8- mediated blast resistance.4.miR160 a controls tiller angle and grain width.Besides,we found that miR160a controls plant architecture and grain size.OX160 a shows an obvious increased tiller angle while knock-out of ARF8 leads to a similar phenotype with the control, indicating miR160 a represses multiple ARFs to control tiller angle.Further analysis implied that the auxin distribution between the lower and upper sides of stem-base was disturbed in OX160 a and MIM160.Furthermore,both of OX160 a and arf8 showed a broader grain width,whereas MIM160 and OXARF8 lines display a grain width narrower than that of NPB or the negative controls.WRKY45 didn’t contribute to the increased grain size of arf8 as the wrky45/arf8 mutants displays an enlarged grain width similar to arf8.These data indicate that the miR160a-ARF8 module coordinates rice immunity and yield traits.