TaCAMTA4, a Calmodulin-Interacting Protein, Involved in Defense Response of Wheat to Puccinia triticina

Leaf rust caused by Puccinia triticina is one of the main diseases affecting wheat ( Triticum aestivum ) production worldwide. Calmodulin (CaM) was found involved in the early stage of signal transduction pathway in response to P . triticina in wheat. To study the function and molecular mechanism of calmodulin (CaM) in signal transduction of wheat against P . triticina , we cloned a putative calmodulin-binding transcription activator ( TaCAMTA4 ), and characterized its molecular structure and functions by using the CaM-encoding gene ( TaCaM4-1) as a bait to screen the cDNA library from P . triticina infected wheat leaves. The open reading frame of TaCAMTA4 was 2505 bp encoding a protein of 834 aa, which contained all the four conserved domains of family (CG-1 domain, TIG domain, ANK repeats and CaM-binding domain). TaCaM4-1 bound to TaCAMTA4 by the C-terminal CaM-binding domain in Ca 2+ -dependent manner in the electrophoretic mobility shift assay (EMSA). Bimolecular fluorescence complementation (BiFC) analysis indicated that the interaction of TaCAMTA4 and TaCaM4-1 took place in the cytoplasm and nucleus of epidermal leaf cells in N . benthamiana . The expression level of TaCAMTA4 genes was down-regulated in incompatible combination after P . triticina infection. Furthermore, virus-induced gene silencing (VIGS)-based knockdown of TaCAMTA 4 and disease assays verified that silencing of TaCAMTA 4 resulted in enhanced resistance to P . triticina race 165. These results suggested that TaCAMTA 4 function as negative regulator of defense response against P . triticina .