NAC Transcription Factor Gene Research Articles

Genome-Wide Identification and Characterization of Yellow Horn (Xanthoceras sorbifolia Bunge) NAC Transcription Factor Gene Family against Diverse Abiotic Stresses

Yellow horn (Xanthoceras sorbifolia Bunge) belonging to the Sapindaceae family is a well-known oil-rich seed shrub widely distributed throughout the northern regions of China, which is preferred owing to its exceptional economic, environmental, ecological and ornamental value. The recent completion of yellow horn genome sequencing facilitates a genome-wide survey of yellow horn transcription factor (TF) families. Plant-specific NAC proteins represent a major TF family in regulating diverse plant biological processes at different tissues and developmental stages. However, no detailed information can be obtained concerning the yellow horn NAC (XsNAC) proteins. Given this, we performed a genome-wide survey of XsNAC gene families. In total 103 putative XsNACs genes were identified from yellow horn genome. Phylogenetic analysis performed between NAC proteins of yellow horn and Arabidopsis revealed that these XsNAC proteins can be classified into 12 subgroups. Gene structure analysis revealed that the intron number of XsNAC genes varied from 0 to 12, and most XsNAC genes had two introns. Conserved motif analysis suggested that all putative XsNAC proteins had conserved NAC domain and/or NAM domain. These predicted XsNAC genes were randomly distributed on 15 chromosomes at diverse densities, particularly on chromosome 1, chromosome 7 and chromosome 11. The cis-regulatory elements (CREs) analysis and protein-protein interaction network analysis showed that the XsNAC proteins may involve in many plant physiological and biochemical processes. Transcriptome analysis revealed that XsNAC genes had differential expression profiles in response to various abiotic stresses, implying their key roles in environmental stress responses. This work would lay solid foundation for future functional characterization of XsNAC proteins.

Role of ethylene in the regulatory mechanism underlying the abortion of ovules after fertilization in Xanthoceras sorbifolium.

Genes related to the MAPK cascade, ethylene signaling pathway, Pi starvation response, and NAC TFs were differentially expressed between normal and abortive ovules. Receptor-mediated ethylene signal perception and transmission play an important role in regulating fruit and ovule development. Xanthoceras sorbifolium, a small to medium-sized tree endemic to northern China, is an emerging dedicated oilseed crop designed for applications in advanced biofuel, engine oil, and functional food, as well as for pharmaceutical and cosmetic applications. Despite the importance of Xanthoceras seed oil, low seed productivity has constricted commercial exploitation of the species. The abortion of developing seeds (ovules after fertilization) is a major factor limiting fruit and seed production in the plant. To increase fruit and seed yields, a better understanding of the mechanisms underlying the abortion of fertilized ovules is critical. This study revealed differences in nucellus degeneration, endosperm development, and starch grain content between normally and abnormally developing ovules after fertilization. We constructed 6 RNA-sequencing (RNA-seq) libraries from normally and abnormally developing ovules at the onset of their abortion process. Comparative transcriptome analysis between the normal and abnormal ovules identified 818 differentially expressed genes (DEGs). Among DEGs, many genes involved in mitogen-activated protein kinase (MAPK) cascades, ethylene signaling pathway, and NAC transcription factor genes showed up-regulated expression in abnormal ovules. The RNA-seq data were validated using quantitative reverse-transcription PCR. Using virus-induced gene silencing (VIGS) methods, evaluation of an ethylene receptor gene (XsERS) function indicated that the gene was closely related to early development of fruits and seeds. Based on the data presented here, we propose a model for a MAPK-ethylene signaling-NAC2 gene regulatory cascade that plays an important role in the regulation of the ovule abortion process in X. sorbifolium. The present study is imperative for understanding the mechanisms of ovule abortion after fertilization and identifying the critical genes and gene networks involved in determining the fate of ovule development.

Comprehensive analysis of NAC transcription factor family uncovers drought and salinity stress response in pearl millet (Pennisetum glaucum)

BackgroundPearl millet (Pennisetum glaucum) is a cereal crop that possesses the ability to withstand drought, salinity and high temperature stresses. The NAC [NAM (No Apical Meristem), ATAF1 (Arabidopsis thaliana Activation Factor 1), and CUC2 (Cup-shaped Cotyledon)] transcription factor family is one of the largest transcription factor families in plants. NAC family members are known to regulate plant growth and abiotic stress response. Currently, no reports are available on the functions of the NAC family in pearl millet.ResultsOur genome-wide analysis found 151 NAC transcription factor genes (PgNACs) in the pearl millet genome. Thirty-eight and 76 PgNACs were found to be segmental and dispersed duplicated respectively. Phylogenetic analysis divided these NAC transcription factors into 11 groups (A-K). Three PgNACs (− 073, − 29, and − 151) were found to be membrane-associated transcription factors. Seventeen other conserved motifs were found in PgNACs. Based on the similarity of PgNACs to NAC proteins in other species, the functions of PgNACs were predicted. In total, 88 microRNA target sites were predicted in 59 PgNACs. A previously performed transcriptome analysis suggests that the expression of 30 and 42 PgNACs are affected by salinity stress and drought stress, respectively. The expression of 36 randomly selected PgNACs were examined by quantitative reverse transcription-PCR. Many of these genes showed diverse salt- and drought-responsive expression patterns in roots and leaves. These results confirm that PgNACs are potentially involved in regulating abiotic stress tolerance in pearl millet.ConclusionThe pearl millet genome contains 151 NAC transcription factor genes that can be classified into 11 groups. Many of these genes are either upregulated or downregulated by either salinity or drought stress and may therefore contribute to establishing stress tolerance in pearl millet.

A functional genomics approach to dissect spotted alfalfa aphid resistance in Medicago truncatula

Aphids are virus-spreading insect pests affecting crops worldwide and their fast population build-up and insecticide resistance make them problematic to control. Here, we aim to understand the molecular basis of spotted alfalfa aphid (SAA) or Therioaphis trifolii f. maculata resistance in Medicago truncatula, a model organism for legume species. We compared susceptible and resistant near isogenic Medicago lines upon SAA feeding via transcriptome sequencing. Expression of genes involved in defense and stress responses, protein kinase activity and DNA binding were enriched in the resistant line. Potentially underlying some of these changes in gene expression was the finding that members of the MYB, NAC, AP2 domain and ERF transcription factor gene families were differentially expressed in the resistant versus susceptible lines. A TILLING population created in the resistant cultivar was screened using exome capture sequencing and served as a reverse genetics tool to functionally characterise genes involved in the aphid resistance response. This screening revealed three transcription factors (a NAC, AP2 domain and ERF) as important regulators in the defence response, as a premature stop-codon in the resistant background led to a delay in aphid mortality and enhanced plant susceptibility. This combined functional genomics approach will facilitate the future development of pest resistant crops by uncovering candidate target genes that can convey enhanced aphid resistance.

Genome-wide identification and comprehensive analyses of NAC transcription factor gene family and expression patterns during somatic embryogenesis in Dimocarpus longan Lour

The NAM, ATAF1/2, and CUC2 form a huge plant-specific gene family of NAC TFs that are involved in the growth, development, and regulation of biotic and abiotic stress responses. Although the draft genome of longan (Dimocarpus longan Lour.) has been published, however the comprehensive data regarding the functions, evolution, and expression patterns of the NAC family are still unavailable. In this study, a comprehensive analysis of the NAC transcription factor family in longan was performed, and a total of 114 NAC genes were found. We investigated the NAC gene family exploring the phylogeny, domain conservation, intron/exon, motifs, cis-regulatory elements, protein-protein interaction, and expression profiles of RNA-seq samples in different tissues and early somatic embryogenesis of longan. Phylogenetic analysis showed that the genes with similar gene structure and motif distribution were clustered in the same group. Cis-element identification indicates the possible role of NAC genes in biological and physiological processes. Protein-protein interaction identified the DlNACs homologous with Arabidopsis proteins. We further investigated the expression pattern of DlNAC genes in different tissues (pulp, stem, large fruit, young fruit, and flower) during somatic embryogenesis at embryogenic callus (EC), incomplete compact pro-embryogenic cultures (ICpEC), and globular embryos (GE) stages. The qRT-PCR results showed that the DlNAC genes were expressed higher at EC and GE stage compared with ICpEC stage. In conclusion, our results provide insight into the evolution, diversity, and characterization of NAC genes in the longan and provide a base for understanding their biological roles and molecular mechanisms in plants.

Comprehensive genomic characterization of NAC transcription factor family and their response to salt and drought stress in peanut

BackgroundPeanut is one of the most important oil crop species worldwide. NAC transcription factor (TF) genes play important roles in the salt and drought stress responses of plants by activating or repressing target gene expression. However, little is known about NAC genes in peanut.ResultsWe performed a genome-wide characterization of NAC genes from the diploid wild peanut species Arachis duranensis and Arachis ipaensis, which included analyses of chromosomal locations, gene structures, conserved motifs, expression patterns, and cis-acting elements within their promoter regions. In total, 81 and 79 NAC genes were identified from A. duranensis and A. ipaensis genomes. Phylogenetic analysis of peanut NACs along with their Arabidopsis and rice counterparts categorized these proteins into 18 distinct subgroups. Fifty-one orthologous gene pairs were identified, and 46 orthologues were found to be highly syntenic on the chromosomes of both A. duranensis and A. ipaensis. Comparative RNA sequencing (RNA-seq)-based analysis revealed that the expression of 43 NAC genes was up- or downregulated under salt stress and under drought stress. Among these genes, the expression of 17 genes in cultivated peanut (Arachis hypogaea) was up- or downregulated under both stresses. Moreover, quantitative reverse transcription PCR (RT-qPCR)-based analysis revealed that the expression of most of the randomly selected NAC genes tended to be consistent with the comparative RNA-seq results.ConclusionOur results facilitated the functional characterization of peanut NAC genes, and the genes involved in salt and drought stress responses identified in this study could be potential genes for peanut improvement.

MiR164-targeted TaPSK5 encodes a phytosulfokine precursor that regulates root growth and yield traits in common wheat (Triticum aestivum L.)

TaPSK5 is a less conserved target of miR164 in wheat encoding a positive regulator of root growthand yield traits that could be used for crop improvement. MicroRNAs (miRNAs) play key roles in regulating plant growth and development by targeting the mRNAs of conserved genes. However, little is known about the roles of less conserved miRNA-targeted genes in plants. In the current study, we identified TaPSK5, encoding a phytosulfokine precursor, as a novel target of miR164. Compared with miR164-targeted NAC transcription factor genes, TaPSK5 is less conserved between monocots and dicots. Expression analysis indicated that TaPSK5 homoeologs were constitutively expressed in wheat tissues, especially young spikes. Overexpression of TaPSK5-D and miR164-resistant TaPSK5-D (r-TaPSK5-D) led to increased primary root growth and grain yield in rice, with the latter having more significant effects. Comparison of the transcriptome between wild-type and r-TaPSK5-D overexpression plants revealed multiple differentially expressed genes involved in hormone signaling, transcription regulation, and reactive oxygen species (ROS) homeostasis. Moreover, we identified three TaPSK5-A haplotypes (TaPSK5-A-Hap1/2/3) and two TaPSK5-B haplotypes (TaPSK5-B-Hap1/2) in core collections of Chinese wheat. Both TaPSK5-A-Hap1 and TaPSK5-B-Hap2 are favorable haplotypes associated with superior yield traits that were under positive selection during wheat breeding. Together, our findings identify miR164-targeted TaPSK5 as a regulator of root growth and yield traits in common wheat with potential applications for the genetic improvement of crops.

Genome-wide analysis of evolution and expression profiles of NAC transcription factor gene family in Juglans regia L.

Key message NAC transcription factors may play important roles in the biological processes in Persian walnut. A total of 102 JrNAC s were identified in Persian walnut. The conserved domains, transcriptome profile, expression analysis, and interaction network suggest that JrNAC1-4 plays potential roles in Persian walnut flowering development. Context NACs are plant-specific transcription factors that participate in various plant developmental processes such as flowering, plant growth regulation, and development. We identified and analyzed the evolution and expression profiles of NAC genes in Juglans regia. Aims The main objectives were to identify the NAC transcription factors and verify the expression levels in different tissues and female flowers in developmental stages in Persian walnut. Methods We identified NAC transcription factors in J. regia based on the genome-wide analysis. We analyzed the phylogenetic relationships, conserved domain, chromosome location, gene structure, and gene collinearity of JrNACs. We also verified the JrNAC expression levels based on transcriptome analysis and qRT-PCR. Results We identified 102 NAC genes in J. regia and divided them into ten subfamilies. A total of 30 pairs of JrNAC genes were expanded by whole-genome duplications (WGDs) and one pair of genes (JrNAC2-10 and JrNAC9-8) as a tandem duplication in Persian walnut. Collinearity analysis results indicate that a large number of syntenic relationship events existed between J. regia and Populus trichocarpa. We found that JrNAC1-4 and JrNAC2-6 were expressed significantly higher in female flowers based on both transcriptome and qPCR analysis. We further identified that JrNAC2-9 and JrNAC9-6 were highly expressed at the end period of flowering stages. Conclusion A total of 102 JrNACs were identified in the Persian walnut genome. These genes were conserved in plants for collinearity analysis, which was performed within the genome and other genomes (P. trichocarpa, Olea europaea, and Quercus robur). A total of 24 NAC transcription factors were highly expressed in female and male flowers, and these transcription factors play a role in J. regia flowering.

An NAC transcription factor gene from Malus baccata, MbNAC29, increases cold and high salinity tolerance in Arabidopsis

NAC (no apical meristem [NAM], Arabidopsis thaliana transcription activation factor [ATAF1/2], and cup-shaped cotyledon [CUC2]) TFs are involved in stress responses in plants. However, their roles in abiotic stresses are still not well known in Malus plants. In the present study, MbNAC29 from Malus baccata was identified and characterized. Quantitative real-time PCR analysis revealed that the expression of MbNAC29 was induced by cold, high salinity, drought, and heat. The open reading frame (ORF) of MbNAC29 is 1122 bp, encodes 373 amino acids. Subcellular localization showed that the MbNAC29-GFP (green fluorescent protein) fusion protein was localized in the nucleus. Furthermore, MbNAC29 was highly expressed in new leaf and mature leaf. When MbNAC29 was introduced into Arabidopsis, it improved cold and high salinity tolerance in transgenic plants under low-temperature stress (− 4°C) and salt stress (200 mM NaCl). When MbNAC29 was introduced into Arabidopsis, it increased the survival rate of transgenic lines than wild type (WT) under cold and high-salinity stresses. In addition, overexpression of MbNAC29 in transgenic Arabidopsis increased the contents of chlorophyll and proline and the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), while decreased the content of malondialdehyde (MDA). Therefore, these results suggest that MbNAC29 probably plays an important role in response to cold and salt stresses in Arabidopsis by enhancing scavenging capability of reactive oxygen species (ROS).

Multiple-population QTL mapping of maturity and fruit-quality traits reveals LG4 region as a breeding target in sweet cherry (Prunus avium L.)

Sweet cherry maturity date and fruit quality are relevant traits for its marketability, transport, and consumer acceptance. In this work, sweet cherry fruit development time, maturity date, and commercial fruit-quality traits (size, weight, firmness, soluble solid content, and titratable acidity) were investigated to improve the knowledge of their genetic control, and to identify alleles of breeding interest. Six sweet cherry populations segregating for these traits were used for QTL analyses. These populations descend from cross- and self-pollinations of local Spanish sweet cherries ‘Ambrunés’ and ‘Cristobalina’, and breed cultivars (‘Brooks’, ‘Lambert’, or ‘Vic’). The six populations (n = 411), previously genotyped with RosBREED Cherry 6 K SNP array, were phenotyped for 2 years. QTL analyses were conducted using a multifamily approach implemented by FlexQTL™. Fruit development time, soluble solid content, and titratable acidity QTLs are first reported in sweet cherry in this work. Significant QTLs were detected for all the traits. Eighteen were more stable as they were detected for 2 years. Of these, nine are first reported in this work. The major QTLs for fruit development time, maturity date, firmness, and soluble solid content were identified on the same narrow region of linkage group 4. These traits also showed significant positive correlation (long fruit development time associated with late maturity, high firmness, and high SSC). NAC transcription factor genes identified on this LG4 region may be candidate genes for the regulation of these traits in sweet cherry, as previously described in syntenic regions of other Rosaceae species. Haplotypes of breeding interest on this LG4 genomic region were identified and will be useful for sweet cherry breeding from this and related plant material.

Ectopic expression of a poplar gene NAC13 confers enhanced tolerance to salinity stress in transgenic Nicotiana tabacum.

NACs are one of the major transcription factor families in plants which play an important role in plant growth and development, as well as in adverse stress responses. In this study, we cloned a salt-inducible NAC transcription factor gene (NAC13) from a poplar variety 84K, followed by transforming it into both Nicotiana tabacum and Arabidopsis thaliana. Stable expression analysis of 35S::NAC13-GFP fusion protein in Arabidopsis indicated that NAC13 protein was localized to the nucleus. We also obtained five transgenic tobacco lines. Evidence from morphological and physiological characterization and salt treatment analyses indicated that in the transgenic tobacco the salt tolerance was enhanced, suggesting that NAC13 gene may function as a positive regulator in tobacco responses to salt stress.

Genome-wide analysis of evolution and expression profiles of NAC transcription factor gene family in Juglans regia L.

Genome-wide analysis of evolution and expression profiles of NAC transcription factor gene family in Juglans regia L.

Genome-wide analysis of evolution and expression profiles of NAC transcription factor gene family in Juglans regia L.

Genome-wide analysis of evolution and expression profiles of NAC transcription factor gene family in Juglans regia L.

Overexpression of grapevine VvNAC08 enhances drought tolerance in transgenic Arabidopsis

NAC [No apical meristem (NAM), Arabidopsis transcription activation factor (ATAF), Cup-shaped cotyledon (CUC)] transcription factors (TFs) play an important role in plant growth and response to various environmental stress. Drought stress is the primary factor limiting the growth and fruit quality of grapevines worldwide. However, the biological function of the NAC family members in grapevine is not clear. In this study, we reported that VvNAC08, a novel NAC transcription factor gene, was expressed after drought, salicylic acid (SA) and abscisic acid (ABA), jasmonic acid (JA) and melatonin (MT) treatments in grapevine. VvNAC08 was expressed in various tissues. The open reading frame (ORF) of VvNAC08 was 792 bp, encoding 263 amino acids. The VvNAC08 protein could bind to NACRS [CGTA/CACG] in yeast. When subjected to drought and dehydration stress, VvNAC08-overexpression (OE) Arabidopsis had a higher survival rate and a lower water loss rate than wild type (WT) plants. Under drought conditions, transgenic Arabidopsis overexpressing VvNAC08 had a lower malondialdehyde (MDA), H2O2 contents, but a higher peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) activities as well as more proline content. Moreover, the expressions of marker genes, including ABI5, AREB1, COR15A, COR47, P5CS, RD22, and RD29A, were up-regulated in VvNAC08-overexpression lines when subjected to drought treatments. The results suggest that the transgenic Arabidopsis overexpressing VvNAC08 enhances resistance to drought while up-regulating the expressions of ABA- and stress-related genes.

Transcriptome profiling of kenaf (Hibiscus cannabinus L.) under plumbic stress conditions implies the involvement of NAC transcription factors regulating reactive oxygen species-dependent programmed cell death.

Heavy metal contamination of soils has become a serious global issue, and bioremediation has been proposed as a potential solution. Kenaf (Hibiscus cannabinus L.) is a fast growing, non-woody multipurpose annual plant that is suitable for removing excess heavy metals from soils. However, there has been relatively little research on the kenaf molecular mechanisms induced in response to an exposure to heavy metal stress. Thus, whole kenaf seedlings grown under control (normal) and stress (plumbic treatment) conditions were sampled for transcriptome sequencing. Unigenes generated through the de novo assembly of clean reads were functionally annotated based on seven databases. Transcription factor (TF)-coding genes were predicted and the physiological traits of the seedlings were analyzed. A total of 44.57 Gb high-quality sequencing data were obtained, which were assembled into 136,854 unigenes. These unigenes included 1,697 that were regarded as differentially expressed genes (DEGs). A GO enrichment analysis of the DEGs indicated that many of them are related to catalytic activities. Moreover, the DEGs appeared to suggest that numerous KEGG pathways are suppressed (e.g., the photosynthesis-involving pathways) or enhanced (like the flavonoid metabolism pathways) in response to Pb stress. Of the 2,066 predicted TF-coding genes, only 55 were differentially expressed between the control and stressed samples. Further analyses suggested that the plumbic stress treatment induced reactive oxygen species-dependent programmed cell death in the kenaf plants via a process that may be regulated by the differentially expressed NAC TF genes.

RNA-Seq transcriptome analysis of Jatropha curcas L. accessions after salt stimulus and unigene-derived microsatellite mining

The small oleaginous tree of Jatropha curcas L. (physic nut) is an excellent biodiesel source whose crop could represent a good income source for farmers in tropical and semi-arid zones. However, in some areas in particular, salinity, such as many other abiotic stresses, can compromise productivity. We analyzed the root RNA-Seq transcriptome of two Brazilian J. curcas accessions after a three-hour NaCl exposition (150 mM) aiming at identifying differentially expressed genes (DEGs) useful for breeding programs. The de novo transcriptome covered 145,422 assembled transcripts (126,343 unigenes), out of which 84,589 showed at least one significant alignment to the GenBank reference genome. Differentially expressed unigenes (DEGs) of the salt-sensitive Jc171 accession (4,646) suppressed those of the salt-tolerant Jc183 (57) one. A MapMan analysis of the DEGs using Manihot esculenta Crantz genes as reference (Euphorbiaceae family) highlighted the metabolism of phytohormone, carbohydrate (CHO), lipid, amino acid, redox, and secondary metabolite in the salt-responses. RT-qPCR results of nine selected Jc183 DEGs [phenylalanine ammonia-lyase (PAL), S-adenosylmethionine-dependent methyltransferase (SAMe), S-adenosylmethionine synthase (SAM), carboxylesterase (CXE), homeobox-leucine zipper gene (HD-Zip), NAC transcription factor gene (NAC), methionine-gamma lyase (MGL), peroxidase (PX), and xyloglucan endotransglucosylase (XTH)] evaluated in 36 combinations accession/treatments validated 86.11 % of the in silico results. The data generated improved the J. curcas transcriptome based on Illumina-21 bp tags as reported before, which can benefit breeders in the improvement of salt-tolerance in J. curcas. Additionally, primer pairs successfully designed for 1,423 DEGs presenting microsatellite motifs can contribute to the development of co-dominant molecular markers, a very useful marker applied to genetic analysis.

Overexpressing the NAC transcription factor LpNAC13 from Lilium pumilum in tobacco negatively regulates the drought response and positively regulates the salt response

NACs are one of the largest transcription factor families in plants and are involved in the response to abiotic stress. A new stress-responsive NAC transcription factor gene, LpNAC13, was isolated from Lilium pumilum bulbs. The expression of LpNAC13 was induced by drought, salt, cold and ABA treatments. LpNAC13 overexpressing plants were generated to explore the function of LpNAC13 in response to drought and salt stress. Overexpression of LpNAC13 in tobacco displayed a reduced drought tolerance but exhibited an enhanced salt tolerance. The LpNAC13 overexpression plants had decreased antioxidant enzyme activities, content of proline and chlorophyll, increased MDA content under drought condition, the results in the LpNAC13 plants under salt condition were opposite to those under drought condition. The seed germination and root length assays of overexpression of LpNAC13 showed decreased sensitivity to ABA. Functional analyses demonstrate that LpNAC13 plays opposite roles in drought and salt stress tolerance, acting as a negative regulator of drought response but as a positive regulator of salt response in tobacco.

Genome-Wide Analysis of NAC Transcription Factors and Characterization of the Cold Stress Response in Sweet Osmanthus

Sweet osmanthus (Osmanthus fragrans) is an evergreen aromatic woody tree widely used in landscaping. However, O. fragrans is very sensitive to cold stress, which seriously limits its cultivation and application in regions of low temperature. The NAC transcription factor gene family which has been characterized in many plant species could participate in multiple processes and play critical roles in plant response to external stress. However, little is known about this family in O. fragrans, an important woody ornamental plant. Here, the structural characteristics, chromosomal location, evolutionary relationship, cold stress expression patterns, and subcellular localization analysis of NAC family genes in O. fragrans were analyzed on a genome-wide scale. A total of 119 O. fragrans NAC genes were identified, and gene structure analysis showed that most OfNACs contained two introns, suggesting that structural diversity of the O. fragrans NAC family is relatively low. The phylogeny evolutionary tree showed that the NACs of O. fragrans were classified into 13 branches. The transcriptome data suggested that each branch members had different expression patterns in various tissues and a number of OfNACs showed tissue-specific expression profiles. The quantitative real-time PCR and subcellular localization results indicated that expression patterns of most branch ‘5B’ members were significantly induced by cold stress and they were mainly located in the nucleus, especially OfNAC49 and 59, indicating that branch ‘5B’ members could have important roles in cold tolerance in O. fragrans. Remarkably, expression levels of many branch ‘5B’ genes were also significantly changed under waterlogging stress, suggesting that this branch might be widely involved in tolerance to various abiotic stresses. Our study should supply useful gene resources for the cold resistance breeding of O. fragrans.

Molecular characterisation and expression analysis of NAC transcription factor genes in wild Medicago falcata under abiotic stresses.

The No apical meristem-Arabidopsis transcription activation factor-Cup-shaped cotyledon (NAC) proteins play vital roles in plant development processes and responses to abiotic stress. In this study, 146 unigenes were identified as NAC genes from wild Medicago falcata L. by RNA sequencing. Among these were 30 full-length NACs, which, except for MfNAC63, MfNAC64 and MfNAC91, contained a complete DNA-binding domain and a variable transcriptional activation region. Sequence analyses of MfNACs along with their Arabidopsis thaliana (L.) Heynh. counterparts allowed these proteins to be phylogenetically classified into nine groups. MfNAC35, MfNAC88, MfNAC79, MfNAC26 and MfNAC95 were found to be stress-responsive genes. The eight MfNAC genes that were chosen for further analysis had different expression abilities in the leaves, stems and roots of M. falcata. Additionally, their expression levels were regulated by salinity, drought and cold stress, and ABA. This study will be useful for understanding the roles of MfNACs in wild M. falcata and could provide important information for the selection of candidate genes associated with stress tolerance.

Analysis of NAC Domain Transcription Factor Genes of Tectona grandis L.f. Involved in Secondary Cell Wall Deposition.

NAC proteins are one of the largest families of plant-specific transcription factors (TFs). They regulate diverse complex biological processes, including secondary xylem differentiation and wood formation. Recent genomic and transcriptomic studies of Tectona grandis L.f. (teak), one of the most valuable hardwood trees in the world, have allowed identification and analysis of developmental genes. In the present work, T. grandis NAC genes were identified and analyzed regarding to their evolution and expression profile during wood formation. We analyzed the recently published T. grandis genome, and identified 130 NAC proteins that are coded by 107 gene loci. These proteins were classified into 23 clades of the NAC family, together with Populus, Eucalyptus, and Arabidopsis. Data on transcript expression revealed specific temporal and spatial expression patterns for the majority of teak NAC genes. RT-PCR indicated expression of VND genes (Tg11g04450-VND2 and Tg15g08390-VND4) related to secondary cell wall formation in xylem vessels of 16-year-old juvenile trees. Our findings open a way to further understanding of NAC transcription factor genes in T. grandis wood biosynthesis, while they are potentially useful for future studies aiming to improve biomass and wood quality using biotechnological approaches.