Background　and　Aims　INDETERMINATE　DOMAIN　10　(IDD10)　is　a　key　transcription　factor　gene　that　activates　the　expression　of　a　large　number　of　NH4+-responsive　genes　including　AMMONIUM　TRANSPORTER　1;2　(AMT1;2).　Primary　root　growth　of　rice　(Oryza　sativa)　idd10　mutants　is　hypersensitive　to　NH4+.　The　involvement　of　CALCINEURIN　B-LIKE　INTERACTING　PROTEIN　KINASE　(CIPK)　genes　in　the　action　of　IDD10　on　NH4+-mediated　root　growth　was　investigated.　Methods　Quantitative　reverse　transcription-PCR　was　used　to　analyse　NH4+-　and　IDD10-dependent　expression　of　CIPK　genes.　IDD10-regulated　CIPK　target　genes　were　identified　using　electrophoretic　mobility　shift　assays,　chromatin　immunoprecipitation　and　transient　transcription　assays.　Root　growth　rate,　ammonium　content　and　N-15　uptake　of　cipk　mutants　were　measured　to　determine　their　sensitivity　to　NH4+　and　to　compare　these　phenotypes　with　those　of　idd10.　The　genetic　relationship　between　CIPK9　OX　and　idd10　was　investigated　by　crosses　between　the　CIPK9　and　IDD10　lines.　Key　Results　AMT1;2　was　overexpressed　in　idd10　to　determine　whether　NH4+-hypersensitive　root　growth　of　idd10　resulted　from　limitations　in　NH4+　uptake　or　from　low　cellular　levels　of　NH4+.　High　NH4+　levels　in　idd10/AMT1;2　OX　did　not　rescue　the　root　growth　defect.　Next,　the　involvement　of　CIPK　genes　in　NH4+-dependent　root　growth　and　interactions　between　IDD10　and　CIPK　genes　was　investigated.　Molecular　analysis　revealed　that　IDD10　directly　activated　transcription　of　CIPK9　and　CIPK14.　Expression　of　CIPK8,　9,　14/15　and　23　was　sensitive　to　exogenous　NH4+.　Further　studies　revealed　that　cipk9　and　idd10　had　almost　identical　NH4+-sensitive　root　phenotypes,　including　low　efficiency　of　(NH4+)-N-15　uptake.　Analysis　of　plants　containing　both　idd10　and　CIPK9　OX　showed　that　CIPK9　OX　could　rescue　the　NH4+-dependent　root　growth　defects　of　idd10.　Conclusions　CIPK9　was　involved　in　NH4+-dependent　root　growth　and　appeared　to　act　downstream　of　IDD10.　This　information　will　be　useful　in　future　explorations　of　NH4+　signalling　in　plants.