NAC Genes Research Articles

Expression of the chickpea CarNAC3 gene enhances salinity and drought tolerance in transgenic poplars

CarNAC3 contains 285 amino acids and a conserved NAC domain. NAC genes, including NAM, ATAF1, ATAF2, and CUC2, are members of one of the largest transcription factor families in plants. CarNAC3, a member of the NAP group, plays an important role in plant development and responses to abiotic stresses. In this study, CarNAC3 was transformed into hybrid poplar plants (Populus deltoides × P. euramericana ‘Nanlin895’) using Agrobacterium tumefaciens. PCR analysis confirmed integration of the introduced T-DNA into the target genome. Reverse transcription PCR confirmed the transformation, and Southern and northern blotting verified the transgene copy number and gene expression, respectively. Fourteen lines of positive transformants were transplanted into a greenhouse to verify their drought and salt tolerances. Under normal conditions, transgenic poplar plants were shorter than the wild-type, but under drought and salt stresses, they maintained their normal rooting and stem growth rates, while those of the wild-type plants were suppressed. Under stress conditions, CarNAC3 expression caused increases in proline and photosynthetic pigment levels and in antioxidant enzyme activities. Furthermore, the expression of CarNAC3 lowered malondialdehyde concentrations compared with the wild-type control. Overall, our results indicated that the CarNAC3 transgene enhanced drought and salt tolerance in transgenic poplar plants.

The abiotic stress-responsive NAC-type transcription factor SlNAC4 regulates salt and drought tolerance and stress-related genes in tomato (Solanum lycopersicum).

SlNAC4 functions as a stress-responsive transcription factor and might be useful for crop salt and drought tolerance improvement. Abiotic stresses, especially salinity and drought, are major factors that significantly limit crop growth and productivity. Plant-specific NAC transcription factors play crucial roles in various stress responses. However, to date only little information regarding stress-related NAC genes is available in tomato. Previously, we reported that tomato SlNAC4-SlNAC10 genes are involved in response of various abiotic stresses. Expression analysis revealed that SlNAC4 was also induced significantly by MeJA, but not by ABA. To further unravel the function of SlNAC4 in response to abiotic stress, we investigated the effects of salt and drought stress on wild-type and SlNAC4-RNAi transgenic tomato plants. The results demonstrated that the root and shoot growth of RNAi plants was more inhibited by salt stress than that of wild-type at post-germination stage. The leaf salt assay also showed less tolerance in transgenic plants by retaining lower chlorophyll content compared with wild-type plants. In addition, transgenic plants became less tolerant to salt and drought stress in soil, which were demonstrated by lower levels of water and chlorophyll contents, and higher water loss rate in their leaves as compared to wild-type plants under stressed conditions. Notably, the expressions of multiple stress-related genes were downregulated in SlNAC4-RNAi plants under both control and salt-stressed conditions. Collectively, these results highlight the important role of SlNAC4 functions as a stress-responsive transcription factor in positive modulation of abiotic stress tolerance through an ABA-independent signaling networks and possibly in response to biotic stress, and may hold promising applications in the engineering of salt- and drought-tolerant tomato.

Tomato NAC transcription factor SlSRN1 positively regulates defense response against biotic stress but negatively regulates abiotic stress response.

Biotic and abiotic stresses are major unfavorable factors that affect crop productivity worldwide. NAC proteins comprise a large family of transcription factors that play important roles in plant growth and development as well as in responses to biotic and abiotic stresses. In a virus-induced gene silencing-based screening to identify genes that are involved in defense response against Botrytis cinerea, we identified a tomato NAC gene SlSRN1 (Solanum lycopersicum Stress-related NAC1). SlSRN1 is a plasma membrane-localized protein with transactivation activity in yeast. Expression of SlSRN1 was significantly induced by infection with B. cinerea or Pseudomonas syringae pv. tomato (Pst) DC3000, leading to 6–8 folds higher than that in the mock-inoculated plants. Expression of SlSRN1 was also induced by salicylic acid, jasmonic acid and 1-amino cyclopropane-1-carboxylic acid and by drought stress. Silencing of SlSRN1 resulted in increased severity of diseases caused by B. cinerea and Pst DC3000. However, silencing of SlSRN1 resulted in increased tolerance against oxidative and drought stresses. Furthermore, silencing of SlSRN1 accelerated accumulation of reactive oxygen species but attenuated expression of defense genes after infection by B. cinerea. Our results demonstrate that SlSRN1 is a positive regulator of defense response against B. cinerea and Pst DC3000 but is a negative regulator for oxidative and drought stress response in tomato.

Citrullus colocynthis NAC transcription factors CcNAC1 and CcNAC2 are involved in light and auxin signaling.

Two novel NAC transcription factors from C itrullus colocynthis implicated in light and auxin signaling pathway. NAC transcription factors (NAM, ATAF1, 2, CUC2) have multiple functions in plant growth and development. Two NACs, CcNAC1 and CcNAC2, were recently identified in the highly drought-tolerant cucurbit species, Citrullus colocynthis. This study examines the functional role of these genes under different qualities of light based on the in silico analysis of the CcNAC1 and CcNAC2 promoters that revealed the presence of several light-associated motifs. The impact of both light and auxin on CcNAC1 and CcNAC2 expression was examined in C. colocynthis leaves, and using reporter (pCcNAC1, 2::GUS) lines in Arabidopsis. Furthermore, the effects of constitutive overexpression (OE-CcNAC1, 2) in Arabidopsis were also examined under a range of conditions to confirm reporter line linkages. White, blue, red, and far-red light treatments resulted in similar patterns of quantitative changes in CcNAC1and CcNAC2 expression in both species, with the highest transcript increases following red light. Photomorphogenic changes in Arabidopsis hypocotyls were correlated with gene transcript levels. In the absence of light, hypocotyls of OE-CcNAC1/CcNAC2 lines were significantly longer as compared to WT. The addition of exogenous auxin (+IAA) to growth medium also resulted in changes to the hypocotyl lengths of overexpression lines and spatiotemporal reporter line changes in seedlings. Our data suggest that CcNAC1, 2 might be functionally important in the light signaling pathway, and appear connected to the hormone auxin. This is the first study to indicate that NAC genes might play a role in both light and auxin signaling pathways.

NAC transcription factor expression, amino acid concentration and growth of elite rice cultivars upon salt stress

NAC transcription factors (TF) play important roles in regulating osmotic stress tolerance in plants. We tested the expression of 57 NAC genes in the presence of NaCl in young leaves of two elite rice cultivars, Cotaxtla and Tres Rios, which display contrasting responses to salinity at the biochemical and physiological levels. Using qRT-PCR, the expression of 41 out of 57 NAC genes was validated, of which 23 showed regulation by NaCl. We identified two NAC genes (Os02g56600 and Os12g07790) induced in Cotaxtla, but repressed in Tres Rios when plants were exposed to 100 mM NaCl in nutrient solution. In both elite cultivars, treated plants showed higher concentrations of total amino acids and proline in comparison to the controls; in all cases, Cotaxtla plants accumulated more free amino acids and proline than Tres Rios plants. Furthermore, shoot growth was more affected in both cultivars, while root length was not reduced in treated plants in comparison to the controls. We conclude that both elite rice cultivars exhibit different expression patterns of NAC transcription factors as well as biochemical and physiological responses to salt stress, giving rise to better performance of Cotaxtla plants in comparison to Tres Rios plants under our experimental conditions.

Genome-wide identification and expression pattern of drought-responsive members of the NAC family in maize

NAC proteins are plant-specific transcription factors (TFs). Although they play a pivotal role in regulating distinct biological processes, TFs in maize are yet to be investigated comprehensively. Within the maize genome, we identified 152 putative NAC domain-encoding genes (ZmNACs), including eight membrane-bound members, by systematic sequence analysis and physically mapped them onto ten chromosomes of maize. In silico analysis of the ZmNACs and comparison with similar genes in other plants such as Arabidopsis, rice, and soybean, revealed a similar NAC sequence architecture. Phylogenetically, the ZmNACs were arranged into six distinct subgroups (I–VI) possessing conserved motifs. Phylogenetic analysis using stress-related NAC TFs from Arabidopsis, rice, and soybean as seeding sequences identified 24 of the 152 ZmNACs (all from Group II) as putative stress-responsive genes, including one dehydration-responsive ZmSNAC1 gene reported earlier. One drought-tolerant genotype (HKI577) and one susceptible genotype (PC13T-3) were used for studying the expression pattern of the NAC genes during drought stress. qRT-PCR based expression profiles of 11 genes predicted to be related to stress confirmed strong differential gene expression during drought stress. Phylogenetic analyses revealed that ZmNAC18, ZmNAC51, ZmNAC145, and ZmNAC72, which were up-regulated in the tolerant genotype and down-regulated in the susceptible genotype, belonged to the same group to which also belong other drought-responsive genes, namely SNAC1, OsNAC6, ANAC019, and ANAC055, which act as a transcriptional activator and are strongly induced under stress from various abiotic sources. Differentially expressed ZmNAC genes, alone or in combination with each other or with other type(s) of TFs, may control the general cellular machinery and regulate stress-responsive downstream genes. Alternatively, they may serve as a platform to regulate a broad set of genes, which are subsequently fine-tuned by specific regulators. This genome-wide identification and expression profiling opens new avenues for systematic functional analysis of new members of the NAC gene family, which may be exploited in developing lines that are better adapted to drought.

Molecular characterization of StNAC2 in potato and its overexpression confers drought and salt tolerance

Potato is one of the most important food crops in the world. Many plant transcription factors (TFs) have been demonstrated to be essential for improvement of plant stress tolerance traits. However, very few TFs were used for improving potato stress tolerance. In this study, we presented the characterization of a new potato StNAC2 gene. The StNAC2 protein contains five subdomains of NAC proteins and belongs to NAP subfamily. StNAC2 is constitutively expressed in potato leaves, stems, tubers, flowers and roots. Transcripts of StNAC2 were significantly induced by Phytophthora infestans, the causal agent pathogen of potato late blight. StNAC2 also could be induced by wounding, salt, drought as well as signal molecules such as salicylic acid and abscisic acid, suggesting that StNAC2 transcription factor involved in the signal transduction cascades in responses to abiotic and biotic stresses in potato. Overexpression of StNAC2 in transgenic potato significantly enhanced salt tolerance in vitro and drought tolerance in pot growing condition. Thus, the functional analysis of the new StNAC2 gene in this study will enrich knowledge for understanding the function of the NAC genes in potato stress tolerance.

Identification of 32 full-length NAC transcription factors in ramie (Boehmeria nivea L. Gaud) and characterization of the expression pattern of these genes

NAM, ATAF, and CUC (NAC) genes are plant-specific transcription factors (TFs) that play key roles in plant growth, development, and stress tolerance. To date, none of the ramie NAC (BnNAC) genes had been identified, even though ramie is one of the most important natural fiber crops. In order to mine the BnNAC TFs and identify their potential function, the search for BnNAC genes against two pools of unigenes de novo assembled from the RNA-seq in our two previous studies was performed, and a total of 32 full-length BnNAC genes were identified in this study. Forty-seven function-known NAC proteins published in other species, in concert with these 32 BnNAC proteins were subjected to phylogenetic analysis, and the result showed that all the 79 NAC proteins can be divided into eight groups (NAC-I-VIII). Among the 32 BnNAC genes, 24, 2, and 1 gene showed higher expression in stem xylem, leaf, and flower, respectively. Furthermore, the expression of 14, 11 and 4 BnNAC genes was regulated by drought, cadmium stress, and infection by root lesion nematode, respectively. Interestingly, there were five BnNAC TFs which showed high homology with the NAC TFs of other species involved in regulating the secondary wall synthesis, and their expressions were not regulated by drought and cadmium stress. These results suggested that the BnNAC family might have a functional diversity. The identification of these 32 full-length BnNAC genes and the characterization of their expression pattern provide a basis for future clarification of their functions in ramie growth and development.

A novel NAC transcription factor from Suaeda liaotungensis K. enhanced transgenic Arabidopsis drought, salt, and cold stress tolerance

Sl NAC1 functions as a stress-responsive NAC protein involved in the abscisic acid-dependent signaling pathway and enhances transgenic Arabidopsis drought, salt, and cold stress tolerance. NAC (NAM, ATAF1, 2, CUC2) transcription factors constitute the largest families of plant-specific transcription factors, known to be involved in various growth or developmental processes and in regulation of response to environmental stresses. However, only little information regarding stress-related NAC genes is available in Suaeda liaotungensis K. In this study, we cloned a full-length NAC gene (1,011 bp) named SlNAC1 using polymerase chain reaction from Suaeda liaotungensis K. and investigated its function by overexpression in transgenic Arabidopsis. SlNAC1 contains an NAC-conserved domain. Its expression in S. liaotungensis was induced by drought, high-salt, and cold (4 °C) stresses and by abscisic acid. Subcellular localization experiments in onion epidermal cells indicated that SlNAC1 is localized in the nucleus. Yeast one-hybrid assays showed that SlNAC1 functions as a transcriptional activator. SlNAC1 transgenic Arabidopsis displayed a higher survival ratio and lower rate of water loss under drought stress; a higher germination ratio, higher survival ratio, and lower root inhibition rate under salt stress; a higher survival ratio under cold stress; and a lower germination ratio and root inhibition rate under abscisic acid treatment, compared with wild-type Arabidopsis. These results suggested that SlNAC1 functions as a stress-responsive NAC protein involved in the abscisic acid-dependent signaling pathway and may have potential applications in transgenic breeding to enhance crops' abiotic stress tolerances.

Conserved miR164-targeted NAC genes negatively regulate drought resistance in rice

MicroRNAs constitute a large group of endogenous small RNAs of ~22 nt that emerge as vital regulators, mainly by targeting mRNAs for post-transcriptional repression. Previous studies have revealed that the miR164 family in Arabidopsis is comprised of three members which guide the cleavage of the mRNAs of five NAC genes to modulate developmental processes. However, the functions of the miR164-targeted NAC genes in crops are poorly deciphered. In this study, the conserved features of six miR164-targeted NAC genes (OMTN1-OMTN6) in rice are described, and evidence is provided that four of them confer a negative regulatory role in drought resistance. OMTN proteins have the characteristics of typical NAC transcriptional factors. The miR164 recognition sites of the OMTN genes are highly conserved in rice germplasms. Deletion of the recognition sites impaired the transactivation activity, indicating that the conserved recognition sites play a crucial role in maintaining the function of the OMTN proteins. The OMTN genes were responsive to abiotic stresses, and showed diverse spatio-temporal expression patterns in rice. Overexpression of OMTN2, OMTN3, OMTN4, and OMTN6 in rice led to negative effects on drought resistance at the reproductive stage. The expression of numerous genes related to stress response, development, and metabolism was altered in OMTN2-, OMTN3-, OMTN4-, and OMTN6-overexpressing plants. Most of the up-regulated genes in the OMTN-overexpressing plants were down-regulated by drought stress. The results suggest that the conserved miR164-targeted NAC genes may be negative regulators of drought tolerance in rice, in addition to their reported roles in development.

Genomic analysis of NAC transcription factors in banana (Musa acuminata) and definition of NAC orthologous groups for monocots and dicots

Identifying the molecular mechanisms underlying tolerance to abiotic stresses is important in crop breeding. A comprehensive understanding of the gene families associated with drought tolerance is therefore highly relevant. NAC transcription factors form a large plant-specific gene family involved in the regulation of tissue development and responses to biotic and abiotic stresses. The main goal of this study was to set up a framework of orthologous groups determined by an expert sequence comparison of NAC genes from both monocots and dicots. In order to clarify the orthologous relationships among NAC genes of different species, we performed an in-depth comparative study of four divergent taxa, in dicots and monocots, whose genomes have already been completely sequenced: Arabidopsis thaliana, Vitis vinifera, Musa acuminata and Oryza sativa. Due to independent evolution, NAC copy number is highly variable in these plant genomes. Based on an expert NAC sequence comparison, we propose forty orthologous groups of NAC sequences that were probably derived from an ancestor gene present in the most recent common ancestor of dicots and monocots. These orthologous groups provide a curated resource for large-scale protein sequence annotation of NAC transcription factors. The established orthology relationships also provide a useful reference for NAC function studies in newly sequenced genomes such as M. acuminata and other plant species.Electronic supplementary materialThe online version of this article (doi:10.1007/s11103-013-0169-2) contains supplementary material, which is available to authorized users.

Members of the barley NAC transcription factor gene family show differential co-regulation with senescence-associated genes during senescence of flag leaves.

The senescence process of plants is important for the completion of their life cycle, particularly for crop plants, it is essential for efficient nutrient remobilization during seed filling. It is a highly regulated process, and in order to address the regulatory aspect, the role of genes in the NAC transcription factor family during senescence of barley flag leaves was studied. Several members of the NAC transcription factor gene family were up-regulated during senescence in a microarray experiment, together with a large range of senescence-associated genes, reflecting the coordinated activation of degradation processes in senescing barley leaf tissues. This picture was confirmed in a detailed quantitative reverse transcription-PCR (qRT-PCR) experiment, which also showed distinct gene expression patterns for different members of the NAC gene family, suggesting a group of ~15 out of the 47 studied NAC genes to be important for signalling processes and for the execution of degradation processes during leaf senescence in barley. Seven models for DNA-binding motifs for NAC transcription factors were designed based on published motifs, and available promoter sequences of barley genes were screened for the motifs. Genes up-regulated during senescence showed a significant over-representation of the motifs, suggesting regulation by the NAC transcription factors. Furthermore, co-regulation studies showed that genes possessing the motifs in the promoter in general were highly co-expressed with members of the NAC gene family. In conclusion, a list of up to 15 NAC genes from barley that are strong candidates for being regulatory factors of importance for senescence and biotic stress-related traits affecting the productivity of cereal crop plants has been generated. Furthermore, a list of 71 senescence-associated genes that are potential target genes for these NAC transcription factors is presented.

Genome-wide analysis of NAM-ATAF1,2-CUC2 transcription factor family in Solanum lycopersicum

NAM, ATAF1,2, and CUC2 (NAC) proteins constitute one of the largest families of plant-specific transcription factors. These proteins have diverse functions in biological processes. Particularly, NAC transcription factors have received considerable attention as regulators in stress signaling pathways. However, little is known about the NAC genes in tomato (Solanum lycopersicum). In this study, 104 NAC genes were identified in the tomato genome. The predicted NAC genes were distributed across all of 12 chromosomes at various densities and were phylogenetically clustered into six groups (I–VI), together with NAC genes from Arabidopsis and rice.The structure and motif compositions of the NAC genes in tomato were also analyzed. Analysis of available microarray data showed that most of the NAC genes in tomato had specific temporal and spatial expression patterns. Moreover, the expression profiles of eight selected NAC genes in tomato were analyzed in different tissues under different abiotic conditions by quantitative real-time RT-PCR. Except for one, all eight selected genes responded to one or more of the abiotic stress treatments. The results of this study provided insights into the classification and putative functions of this family.

Molecular cloning and functional analysis of NAC family genes associated with leaf senescence and stresses in Gossypium hirsutum L.

The NAC domain genes encode a large family of plant-specific transcription factors that play diverse roles in plant development and stress regulation. In this study, a total of 60 full-length putative NAC genes were isolated from Gossypium hirsutum L. Based on their phylogeny, all GhNAC genes were clustered into seven distinct subfamilies, which exhibit functional similarity. Similarly, a phylogenetic tree for GhNAC genes and their motif showed close resemblance among the subfamilies. The isolated 60 full-length GhNAC genes were located on 13 different chromosomes of D sub-genome. Majority of the NACs showed specific temporal and spatial expression patterns in tissue-specific (fibers, cotyledon leaf, mature leaf, stem, root and flower) studies based on qRT-PCR analyses. Furthermore, the roles of GhNAC genes were monitored using qRT-PCR during leaf senescence and following treatment with ethylene, abscisic acid, gibberellic acid and drought or salinity. This first comprehensive study of GhNAC family elucidates the essential role of these genes in cotton development and in response to various stresses. This study lays fundamental foundations for future research and development in cotton genome.

Overexpression of Rice NAC Gene SNAC1 Improves Drought and Salt Tolerance by Enhancing Root Development and Reducing Transpiration Rate in Transgenic Cotton

The SNAC1 gene belongs to the stress-related NAC superfamily of transcription factors. It was identified from rice and overexpressed in cotton cultivar YZ1 by Agrobacterium tumefaciens-mediated transformation. SNAC1-overexpressing cotton plants showed more vigorous growth, especially in terms of root development, than the wild-type plants in the presence of 250 mM NaCl under hydroponic growth conditions. The content of proline was enhanced but the MDA content was decreased in the transgenic cotton seedlings under drought and salt treatments compared to the wild-type. Furthermore, SNAC1-overexpressing cotton plants also displayed significantly improved tolerance to both drought and salt stresses in the greenhouse. The performances of the SNAC1-overexpressing lines under drought and salt stress were significantly better than those of the wild-type in terms of the boll number. During the drought and salt treatments, the transpiration rate of transgenic plants significantly decreased in comparison to the wild-type, but the photosynthesis rate maintained the same at the flowering stage in the transgenic plants. These results suggested that overexpression of SNAC1 improve more tolerance to drought and salt in cotton through enhanced root development and reduced transpiration rates.

Novel NAC transcription factor TaNAC67 confers enhanced multi-abiotic stress tolerances in Arabidopsis.

Abiotic stresses are major environmental factors that affect agricultural productivity worldwide. NAC transcription factors play pivotal roles in abiotic stress signaling in plants. As a staple crop, wheat production is severely constrained by abiotic stresses whereas only a few NAC transcription factors have been characterized functionally. To promote the application of NAC genes in wheat improvement by biotechnology, a novel NAC gene designated TaNAC67 was characterized in common wheat. To determine its role, transgenic Arabidopsis overexpressing TaNAC67-GFP controlled by the CaMV-35S promoter was generated and subjected to various abiotic stresses for morphological and physiological assays. Gene expression showed that TaNAC67 was involved in response to drought, salt, cold and ABA treatments. Localization assays revealed that TaNAC67 localized in the nucleus. Morphological analysis indicated the transgenics had enhanced tolerances to drought, salt and freezing stresses, simultaneously supported by enhanced expression of multiple abiotic stress responsive genes and improved physiological traits, including strengthened cell membrane stability, retention of higher chlorophyll contents and Na+ efflux rates, improved photosynthetic potential, and enhanced water retention capability. Overexpression of TaNAC67 resulted in pronounced enhanced tolerances to drought, salt and freezing stresses, therefore it has potential for utilization in transgenic breeding to improve abiotic stress tolerance in crops.

Studies on the role of the SlNAC3 gene in regulating seed development in tomato (Solanum lycopersicum)

SummaryPlant seeds contain the sporophytic embryo and nutrients for embryo development. To ensure correct seed formation, co-ordination between the embryo, the endosperm, and the maternal seed components must be achieved. However, this regulatory mechanism is poorly understood. Here, we demonstrate that an NAC gene (SlNAC3) was essential for young embryo and endosperm development in tomato (Solanum lycopersicum). Transgenic tomato seeds expressing SlNAC3 RNA interference (RNAi) exhibited defects in pollen viability and a reduced seed size. Ultrastructural analysis revealed the absence of an embryo sac, while the endosperm collapsed in the seed of transgenic tomato plants expressing lower levels of SlNAC3 transcripts due to RNAi. Real-time quantitative RT-PCR analysis revealed the down-regulation (to < 10% of wild-type levels) of four genes involved in jasmonic acid (JA) biosynthesis in the flowers of transgenic plants. These results demonstrate that the SlNAC3 gene plays a critical role in the development of the embryo in tomato seed.

Structural analysis and tissue-specific expression patterns of a novel salt-inducible NAC transcription factor gene from Nicotiana tabacum cv. Xanthi

SummaryThe NAC (acronym derived from the names of the first three cloned genes NAM, ATAF1/ATAF2, and CUC) transcription factor family is important for plant development and environmental stress responses. We isolated NtNAC2, a new salt-inducible gene in the NAC gene family from tobacco (Nicotiana tabacum var. Xanthi). NtNAC2 encoded 311 amino acids and the deduced protein sequence contained five typical NAC transcription factor domains. Most of the secondary structure of the predicted NtNAC2 protein was made up of αhelices and βsheets. We analysed tissue-specific expression profiles and found that the NtNAC2 gene was expressed mainly in roots, stems, and flowers. We were able to induce NtNAC2 gene expression by exposing tobacco plants to high levels of salt. A phylogenetic analysis of putative NAC-family proteins from the tobacco genome indicated a wide diversity of family members. Our results suggest that the NtNAC2 gene may play an important role in the tolerance of tobacco to salinity.

Genome wide analysis of the NAC transcription factor family in Chinese cabbage to elucidate responses to temperature stress

The NAC is a large family of transcription factors with many functions, involved in developmental and physiological processes. The present study involved a comprehensive analysis of NAC family transcription factors in Chinese cabbage. A total of 188 putative NAC factors were found and identified based on genome of Chinese cabbage. These BraNAC transcription factors were classified into 18 subgroups by sequence similarity. The amino acid sequence, phylogenetic tree and conserved domain were predicted and analyzed. Three motifs in NAC proteins were discovered, which were related to NAC domain construction. The analysis results showed that the NAC factors from Chinese cabbage and Arabidopsis had high similarity. The sequences of 188 NAC genes were distributed unevenly among the 10 chromosomes of the Chinese cabbage genome. Chromosomal locations showed that chromosomal duplication might result in expansion of the NAC genes in Chinese cabbage. Seven NAC genes, chosen from seven subgroups respectively, were further tested for temperature stress responses using real-time quantitative PCR analysis. In total, seven BraNAC genes were differentially expressed under cold or heat stress treatments in the two varieties of Chinese cabbage. This study advances the functional analysis of NAC transcription factors in Brassica.

Molecular Characterization and Expression Analysis of NAC Family Transcription Factors in Tomato

The NAC family is considered one of the largest plant-specific transcription factors families, and functions in diverse and vital physiological processes during development. In the present study, we performed a complete bioinformatics analysis of the NAC family transcription factors in tomato, and annotated the non-redundant SlNAC1-74 proteins into 12 subgroups. Six NAC genes from tomato, which were designated SNAC4–SNAC9, were studied instensively. The expression analysis indicated that each SNAC gene exhibited a specific expression pattern in the tissues examined. SNAC4 and SNAC6 were most highly expressed in the stems and leaves, whereas the expression levels of SNAC5, SNAC8 and SNAC9 were higher in young leaves and old leaves, respectively. In addition, the expression patterns of SNAC genes were characterized during the development of tomato fruits. All of the genes were further investigated to determine their responsiveness to hormones, and a coordinated expression was observed. The expression of the SNAC gene transcripts was induced by ABA, SA and short-time ethylene treatment, whereas their transcription was inhibited by GA, 6-BA and IAA. Our present study provides a useful reference for future investigations of NAC genes in tomato and other fleshy fruits.