Genome-Wide Sequence and Expression Analysis of the NAC Transcription Factor Family in Polyploid Wheat

Many important genes in agriculture correspond to transcription factors which regulate a wide range of pathways from flowering to responses to disease and abiotic stresses. In this study, we identified 5,776 transcription factors in hexaploid wheat (Triticum aestivum) and classified them into gene families. We further investigated the NAC family exploring the phylogeny, C-terminal domain conservation and expression profiles across 308 RNA-seq samples. Phylogenetic trees of NAC domains indicated that wheat NACs divided into eight groups similar to rice (Oryza sativa) and barley (Hordeum vulgare). C-terminal domain motifs were frequently conserved between wheat, rice and barley within phylogenetic groups, however this conservation was not maintained across phylogenetic groups. Three homoeologous copies were present for 58% of NACs, whereas evidence of single homoeolog gene loss was found for 33% of NACs. We explored gene expression patterns across a wide range of developmental stages, tissues, and abiotic stresses. We found that more phylogenetically related NACs shared more similar expression patterns compared to more distant NACs. However, within each phylogenetic group there were clades with diverse expression profiles. We carried out a co-expression analysis on all wheat genes and identified 37 modules of co-expressed genes of which 23 contained NACs. Using GO term enrichment we obtained putative functions for NACs within co-expressed modules including responses to heat and abiotic stress and responses to water: these NACs may represent targets for breeding or biotechnological applications. This study provides a framework and data for hypothesis generation for future studies on NAC transcription factors in wheat.

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