Overexpression of durum wheat NAC transcription factor TtNTL3A promotes early flowering and increases multiple stress tolerance in transgenic Arabidopsis.

Plant-specific NAC transcription factors play important roles in plant development processes, hormone signaling and response to biotic and abiotic stresses. Here, a newly identified membrane-bound NAC gene, designated as TtNTL3A, was isolated from durum wheat. TtNTL3A was homologous to bread wheat TaNAC8 and rice OsNAC8. Moreover, yeast trans-activation assays revealed that TtNTL3A is a transcriptional activator. TtNTL3A was highly expressed in developing seeds and was induced by abiotic stresses, abscisic acid treatment and the infection with Fusarium graminearum. Besides, Transgenic Arabidopsis overexpressing TtNTL3A showed early flowering phenotype and higher tolerance to salt and drought stresses. RT-qPCR analysis revealed that drought and salt-responsive genes were highly expressed in transgenic lines compared to WT plants. Besides, these lines showed resistance to Fusarium graminearum, which was accompanied by a higher expression of pathogenesis-related genes (AtPR-1, Atpdf1.2, and AtNPR1) in TtNTL3A-OE lines. These findings suggest that TtNTL3A is an interesting target of genetic engineering to improve wheat tolerance to biotic and abiotic stresses.

Identification and expression analysis of the NAC transcription factor family in durum wheat (Triticum turgidum L. ssp. durum).

The NAC (NAM, ATAF and CUC) proteins belong to one of the largest plant-specific transcription factor (TF) families and play important roles in plant development processes, response to biotic and abiotic cues and hormone signaling. Our analysis led to the identification of 168 NAC genes in durum wheat, including nine putative membrane-bound TFs and 48 homeologous genes pairs. Phylogenetic analyses of TtNACs along with their Arabidopsis, grape, barley and rice counterparts divided these proteins into 8 phylogenetic groups and allowed the identification of TtNAC-A7, TtNAC-B35, TtNAC-A68, TtNAC-B69 and TtNAC-A43 as homologs of OsNAC1, OsNAC8, OsNTL2, OsNTL5 and ANAC025/NTL14, respectively. In silico expression analysis, using RNA-seq data, revealed tissue-specific and stress responsive TtNAC genes. The expression of ten selected genes was analyzed under salt and drought stresses in two contrasting tolerance cultivars. This analysis is the first report of NAC gene family in durum wheat and will be useful for the identification and selection of candidate genes associated with stress tolerance.