Abstract
The NAC genes, a large plant-specific family of transcription factors, regulate a wide range of pathways involved in development and response to biotic and abiotic stress. In this study, the NAC transcription factors were identified in 27 green plants, and the results showed that NAC transcription factors in plants undergo an appearance stage from water to land and a number expansion stage from gymnosperm to angiosperm. Investigating the evolutionary process of the NAC transcription factors from diploid species to hexaploid wheat revealed that tandem replications during the polyploidization process is an important event for increasing the number of NAC transcription factors in wheat. Then, the molecular characteristics, phylogenetic relationships, and expression patterns of 462 NAC transcription factors of hexaploid wheat (TaNACs) were analyzed. The protein structure results showed that TaNAC was relatively conservative at the N-terminal that contains five subdomains. All these TaNACs were divided into Group I and Group II by phylogenetic analysis, and the TaNACs in Group I should undergo strong artificial selection based on single nucleotide polymorphism (SNP) analysis. Through genome synteny and phylogenetic analysis, these TaNACs were classified into 88 groups and 9 clusters. The biased expression results of these TaNACs showed that there are 24 groups and 67 groups of neofunctionalization genes under biotic and abiotic stress, respectively, and 16 groups and 59 groups of subfunctionalization genes. This shows that neofunctionalization plays an important role in coping with different stresses. Our study provides new insights into the evolution of NAC transcription factors in hexaploid wheat.
Highlights
Transcription factors, known as trans-acting factors, could bind to specific DNA sequences in the promoter region of the target gene to activate or inhibit the transcription of associated genes
To identify the NAC transcription factors in green plants, we performed an identification of NAC transcription factors in hexaploid wheat (AABBDD), Triticum urartu (AA), Aegilops tauschii (DD), Triticum turgidum (AABB), and 23 other green plants with the published genome-data
The results showed that the NAC transcription factors were first identified in the bryophyte (Physcomitrella patens), indicating that these genes appeared as plants transitioned from water to land
Summary
Transcription factors, known as trans-acting factors, could bind to specific DNA sequences in the promoter region of the target gene to activate or inhibit the transcription of associated genes. NAC is named after three gene fragments discovered in the 1970s, namely NAM (no apical meristem), ATAF 1/2 (Arabidopsis transcription activator factor 1/2), and CUC2 (cup-shaped cotyledon) [1,2,3]. It is a type of transcription factor specific to plants; it has multiple functions, and its proteins can usually be divided into two parts: the conserved N-terminal DNA-binding domain and highly differentiated C-terminal transcriptional regulatory regions [4,5,6,7]. Many studies have reported that NAC transcription factors are involved in a wide range of processes, including plant growth and development, organ formation, signal transduction, and regulating the response to environmental stress [6,9,10,11,12]
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