Background:　Loose　Plant　Architecture　1　(LPA1),　an　indeterminate　domain　(IDD)　protein,　exhibits　almost　no　expression　in　the　leaves,　but　the　overexpression　of　LPA1　significantly　increases　the　resistance　of　rice　to　sheath　blight　disease　(ShB)　via　the　activation　of　PIN-FORMED　1a　(PIN1a).　Results:　In　this　study,　we　determined　that　Rhizoctonia　solani　infection　significantly　induced　LPA1　expression　in　the　leaves,　and　lpa1　was　more　susceptible　to　R.　solani　compared　with　the　wild-type　and　revertant　plants.　In　addition,　infection　with　R.　solani　altered　the　expression　of　IDD3,　IDD5,　IDD10,　and　IDD13,　and　yeast　two-hybrid,　split-GFP,　and　coimmunoprecipitation　assays　showed　that　LPA1　interacts　with　IDD3　and　IDD13.　IDD13　RNAi　plants　were　more　susceptible,　while　IDD13　overexpressors　were　less　susceptible　to　ShB　compared　with　the　wild-type.　In　parallel,　idd3　exhibited　no　significant　differences,　while　IDD3　overexpressors　were　more　susceptible　compared　to　the　wild-type　response　to　ShB.　Additional　chromatin-immunoprecipitation　and　electrophoretic　mobility　shift　assay　experiments　indicated　that　IDD13　and　IDD3　bound　to　the　PIN1a　promoter,　and　the　transient　assay　indicated　that　IDD13　and　IDD3　positively　and　negatively　regulate　PIN1a　expression,　respectively.　Moreover,　IDD13,　IDD3,　and　LPA1　form　a　transcription　factor　complex　that　regulates　PIN1a.　A　genetic　study　showed　that　the　LPA1　repressor　lines　were　similar　to　lpa1/IDD13　RNAi　and　were　more　susceptible　than　the　lpa1　and　IDD13　RNAi　plants　in　response　to　ShB.　The　overexpression　of　IDD13　increased　resistance　to　ShB　in　the　lpa1　background.　Conclusions:　Taken　together,　our　analyses　established　that　IDD3,　IDD13,　and　LPA1　form　a　transcription　factor　complex　to　regulate　the　defense　of　rice　against　ShB　possibly　via　the　regulation　of　PIN1a.　©　2020,　The　Author(s).