Abstract
NAC transcription factors are one of the largest families of transcriptional regulators in plants, and members of the gene family play vital roles in regulating plant growth and development processes including biotic/abiotic stress responses. However, little information is available about the NAC family in pitaya. In this study, we conducted a genome-wide analysis and a total of 64 NACs (named HuNAC1-HuNAC64) were identified in pitaya (Hylocereus). These genes were grouped into fifteen subgroups with diversities in gene proportions, exon–intron structures, and conserved motifs. Genome mapping analysis revealed that HuNAC genes were unevenly scattered on all eleven chromosomes. Synteny analysis indicated that the segmental duplication events played key roles in the expansion of the pitaya NAC gene family. Expression levels of these HuNAC genes were analyzed under cold treatments using qRT-PCR. Four HuNAC genes, i.e., HuNAC7, HuNAC20, HuNAC25, and HuNAC30, were highly induced by cold stress. HuNAC7, HuNAC20, HuNAC25, and HuNAC30 were localized exclusively in the nucleus. HuNAC20, HuNAC25, and HuNAC30 were transcriptional activators while HuNAC7 was a transcriptional repressor. Overexpression of HuNAC20 and HuNAC25 in Arabidopsis thaliana significantly enhanced tolerance to cold stress through decreasing ion leakage, malondialdehyde (MDA), and H2O2 and O2− accumulation, accompanied by upregulating the expression of cold-responsive genes (AtRD29A, AtCOR15A, AtCOR47, and AtKIN1). This study presents comprehensive information on the understanding of the NAC gene family and provides candidate genes to breed new pitaya cultivars with tolerance to cold conditions through genetic transformation.
Highlights
Transcription factors (TFs) and cis-elements function in the promoter region of different stress-related genes, and thereby alter their expression in response to the stress tolerance [1,2]
To identify pitaya NAC TF encoding genes, all proteins were annotated from the H. undatus genome [36]
In summary, this study provides the first report on identification and characterization of the NAC gene family based on the genome-wide analyses of the H. undatus genome
Summary
Transcription factors (TFs) and cis-elements function in the promoter region of different stress-related genes, and thereby alter their expression in response to the stress tolerance [1,2]. Many plant TFs, including MYB, bHLH, AP2, MYC, WRKY, and NAC, have been identified and play diverse functions in various biological processes [3]. The name of the NAC gene family was derived from the three earliest characterized proteins with a particular domain (NAC domain) from petunia NAM (no apical meristem), Arabidopsis ATAF1/2, and CUC2 (cup-shaped cotyledon) [6,7]. Protein sequences of this family reveal that a typical NAC TF has a highly conserved NAC domain with about 160 amino acid residues at the N-terminal region while the C-terminal region is highly diversified in length and sequence, which is considered the transcriptional activation domain [8]. The NAC domain is further divided into five subdomains (A–E) that represent motifs for both DNA-binding and protein–protein interactions [9]
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