Characterization Of Two Novel Wheat NAC Transcription Factor Genes Involved In Defense Response Against Stripe Rust

Stripe rust, caused by Puccinia striiformis f. sp. Trittici, is a devastating disease diseases in wheat. Using the resistance cultivars is the safest and most economic and efficient way in controlling the disease. Therefore, analyzing the iteraction and molecular mechnism between wheat and stripe rust is important for the sustainable control of wheat stripe rust.Proteins encoded by the NAC gene family constitute one of the largest plant-specific transcription factors, which have been identified to play many important roles in both abiotic and biotic stress adaptation, as well as in plant development regulation. Protein of this family contains a highly conserved N-terminal DNA-binding domain defined as the NAC domain (for NAM, ATAF1/2, CUC2), and a variable C-terminal domain.In this study, OsNAC4 and OsNAC8 were used as the initial probe to screen the wheat EST database in GenBank, individually. After efficient in silico extension, we isolate a novel wheat NAC genes from wheat, TaNAC4 (GenBank No.GQ985329) and TaNAC8 (GenBank No. GU001723), using reverse transcription PCR (RT-PCR) and RACE methods.TaNAC4 sharing high homology with rice OsNAC4 gene was predicted to encode a protein of 308 amino acid residues, which contained a plant-specific NAC domain in the N-terminus. Transient expression analysis indicated that the deduced TaNAC4 protein was localized in the nucleus of onion epidemical cells. Yeast one-hybrid assay revealed that the C-terminal region of the TaNAC4 protein had transcriptional activity. The expression of TaNAC4 was largely higher in the wheat seedling roots, than that in leaves and stems. TaNAC4 transcript in wheat leaves was induced by the infection of strip rust pathogen, and also by exogenous applied methyl jasmonate (MeJA), ABA and ethylene. However, salicylic acid (SA) had no obvious effect on TaNAC4 expression. Environmental stimuli, including high salinity, wounding, and low-temperature also induced TaNAC4 expression. These results indicate that this novel TaNAC4 gene functions as a transcriptional activator involved in wheat response to biotic and abiotic stresses. TaNAC8 sharing high homology with rice OsNAC8 gene was predicted to encode a protein of 481 amino acid residues. The encoded TaNAC8 protein contained a NAC domain (9-159) in the N-terminus and a transmembrane helices (TM) motif in the C-terminus (451–470). Yeast one-hybrid assay revealed that the C-terminal region of the TaNAC8 protein had transcriptional activity. The expression of TaNAC8 was predominantly expressed in leaves and roots, while weakly in stems. The expression of TaNAC8 in wheat leaves were induced by the infection of strip rust pathogen in the incompatible interaction at 24 hpi, and also by exogenous applied methyl jasmonate (MeJA) and ethylene (ET). However, salicylic acid (SA) and ABA had no obvious effect on TaNAC8 expression. Environmental stimuli, including high salinity, drought, and low-temperature also enhanced TaNAC8 expression. These results indicate that the novel TaNAC8 gene functions as a transcriptional activator involved in wheat defense responses to biotic and abiotic stresses.