NAC Genes Research Articles

Correspondence between maturity date and molecular variations in a NAC transcription factor of diploid and polyploid Prunus species

The maturity date (MD) of Prunus stone fruit has been long known to be a quantitatively inherited trait. A NAC -type gene indicated as PpNAC1 (ppa008301m) has been found recently to be a strong candidate of a major gene influencing MD in peach. A 9-bp insertion in this gene resulted in earlier MD in two segregating peach populations. This study was carried out to test whether this mutation in the PpNAC1 gene can be used as a reliable functional marker for MD in a wide range of peach cultivars of various origins and phenotypic characters. A total of 125 peach cultivars were examined using a 3 × 3 custom chi-square contingency table according to their NAC genotype and MD (early, midseason, and late). Cramer's V equaled 0.478 and the Goodman-Kruskal index (l) was 0.37, indicating an extremely strong correlation between MD and NAC genotype. In addition, we determined 15 sequences from 10 cultivars of five Prunus species including peach, almond, apricot, sour cherry, and European plum with E-values ranging from 9e-88 to 2e-74, supporting their homology to PpNAC1 . A total of 69 single nucleotide polymorphisms and two insertion/deletions were detected in the coding region of the partial NAC domain sequences with three mutations putatively inducing nonconservative amino acid replacements and a nonsense mutation in specific alleles of early ripening apricot and sour cherry cultivars. The results are discussed with focus on the putative molecular mechanisms of mutations in the NAC genes, crop evolutionary perspectives, and the opportunities for designing cost-efficient markers to predict MD in Prunus breeding programs.

Construction of GmNAC085 vector for future development of drought-tolerant crops

Various members of NAC transcription factor family have been shown to play important roles in regulating plant responses to abiotic stresses, such as drought, cold and salinity. Our previous research on differential expression patterns of twenty three soybean NAC genes (GmNACs) by realtime quantitative PCR suggested a correlation between inducible expression of GmNAC085 and the drought tolerance degree in DT51 and MTD720 soybean cultivars, which presented for the drought-tolerant and the drought-sensitive, respectively. Therefore, the gene has been proposed as a potential candidate for engineering in order to produce new varieties with better drought stress tolerance. However, functional studies of GmNAC085 should be carried out to identify how this transcriptional factor can contribute in the plant stress-responsive pathway. Herein, this paper presented that we have successfully developed a recombinant binary vector carrying full-length cDNA of GmNAC085 and expression of this gene is placed under the control of constitutive promoter CaMV 35S. The generated construct was firstly transformed into E.coli for sequencing the target gene and then the identified genuine construct was transformed into Agrobacterium tumefaciens. This can be used for plant transformation mediated by Agrobacterium in serving for GmNAC085 - related studies using in planta system such as the model plant Arabidopsis and also serving for the development of drought-tolerant crops by genetic engineering. Additionally, results from sequence alignment analysis revealed that GmNAC085s of DT51 and MTD720 had identical nucleotide sequence, thus supporting our hypothesis that difference in GmNAC085 gene expression levels, not the variation in GmNAC085 protein sequence or structure, might cause the difference in plant resistance degree to drought stress in these two soybean varieties.

Lateral Root Development in Potato Is Mediated by Stu-mi164 Regulation of NAC Transcription Factor.

The NAC designation is derived from petunia (Petunia hybrida) gene NO APICAL MERISTEM (NAM) and Arabidopsis genes ATAF1/ATAF2 and CUP-SHAPED COTYLEDON2 (CUC2), which belongs to the family of plant-specific transcription factors (TFs), and plays important role in plant development processes, such as response to biotic and abiotic stress, and hormone signaling. MicroRNAs (miRNAs) are a class of small, non-coding endogenous RNAs which play versatile and significant role in plant stress response and development via negatively affecting gene expression at a post-transcriptional level. Here, we showed that Stu-mi164 had a complementary sequence in the CDS sequence of potato NAC TFs, and that NAC expression exhibited significant differences under osmotic stress. We measured expression levels of the Stu-mi164 target gene StNAC262 between control and PEG-treated plants using real-time PCR, and the results demonstrated that they had inverse relationship. We suggested that Stu-miR164 might drive overexpression of NAC gene under osmotic stress in potato. To confirm the regulation of NAC TFs by Stu-mi164, we developed transgenic plants, using Agrobacterium tumefaciens–mediated transformation, of the potato cultivars “Gannongshu 2” and “Kexin 3” overexpressing the Stu-mi164 or the TF StNAC262. Real-time PCR analysis of transgenic potato plants under osmotic (PEG) stress, showed that potato plants overexpressing Stu-mi164 had reduced expression of StNAC262 and their osmotic resistance decreased. Furthermore, these plants had low number of lateral roots although the same length as the control. Our findings support the regulatory role of Stu-miRNAs in controlling plant response to osmotic stress via StNAC262.

Transcript Profiling Identifies NAC-Domain Genes Involved in Regulating Wall Ingrowth Deposition in Phloem Parenchyma Transfer Cells of Arabidopsis thaliana.

Transfer cells (TCs) play important roles in facilitating enhanced rates of nutrient transport at key apoplasmic/symplasmic junctions along the nutrient acquisition and transport pathways in plants. TCs achieve this capacity by developing elaborate wall ingrowth networks which serve to increase plasma membrane surface area thus increasing the cell's surface area-to-volume ratio to achieve increased flux of nutrients across the plasma membrane. Phloem parenchyma (PP) cells of Arabidopsis leaf veins trans-differentiate to become PP TCs which likely function in a two-step phloem loading mechanism by facilitating unloading of photoassimilates into the apoplasm for subsequent energy-dependent uptake into the sieve element/companion cell (SE/CC) complex. We are using PP TCs in Arabidopsis as a genetic model to identify transcription factors involved in coordinating deposition of the wall ingrowth network. Confocal imaging of pseudo-Schiff propidium iodide-stained tissue revealed different profiles of temporal development of wall ingrowth deposition across maturing cotyledons and juvenile leaves, and a basipetal gradient of deposition across mature adult leaves. RNA-Seq analysis was undertaken to identify differentially expressed genes common to these three different profiles of wall ingrowth deposition. This analysis identified 68 transcription factors up-regulated two-fold or more in at least two of the three experimental comparisons, with six of these transcription factors belonging to Clade III of the NAC-domain family. Phenotypic analysis of these NAC genes using insertional mutants revealed significant reductions in levels of wall ingrowth deposition, particularly in a double mutant of NAC056 and NAC018, as well as compromised sucrose-dependent root growth, indicating impaired capacity for phloem loading. Collectively, these results support the proposition that Clade III members of the NAC-domain family in Arabidopsis play important roles in regulating wall ingrowth deposition in PP TCs.

Hydrogen Peroxide-Induced Oxidative Stress in Sugarcane and Response Expression Pattern of Stress-Responsive Genes Through Quantitative RT-PCR

Economic production of sugarcane is highly affected by oxidative stress due to biotic and abiotic stress factors. The main objective of this study was to determine which concentration of hydrogen peroxide can induce the oxidative stress conditions in sugarcane and determine whether several key gene expression responses reported in other species are triggered in sugarcane. Sixty-day-old sugarcane plants were sprayed with 30% H2O2 (300, 500 and 1000 ppm) for three consecutive days. Controls were maintained by spraying with water. Quantitative RT-PCR was performed to quantify the gene expression levels. The PCR products were cloned and sequenced to confirm the identity of the gene amplified. The representative sequences of the stress-responsive genes were deposited in GenBank (Acc. No KX828698 for HSP gene, KX828699 for APX gene, KX828700 for NAC transcription factor and KX828701 for ERF transcription factor). The expression pattern of stress-responsive key genes (HSP, NAC, ERF, GST, MYBAS and CAT) showed higher expression levels within 48 h of H2O2 treatment at 500 and 1000 ppm concentration. However, MYBAS transcription factor and catalase genes showed higher expression levels at a higher concentration of H2O2 (1000 ppm) of H2O2 at 48 h of treatment. Ascorbate peroxidase gene was up-regulated at 1000 ppm of H2O2 at 72 h of treatment. NAC transcription factor, heat shock proteins, ethylene-responsive factor and glutathione S-transferase showed a significant increase in expression at 500 ppm concentration of H2O2 at 48 h. Based on the expression pattern levels, 500 ppm of hydrogen peroxide at 48 h can induce the oxidative stress in sugarcane. The expression levels indicated that HSP, NAC, ERF, GST and MYBAS genes might play a role in signal transduction pathways, and APX and CAT are involved in scavenging reactive oxygen species.

Expression analysis of NAC genes during the growth and ripening of apples

Plant-specific NAC transcription factors (TFs) play crucial roles in various pathways related to the stress response. However, to date, little information regarding NAC gene regulation during fruit ripening is available for the apple (Malus domestica). Here, we report that 13 out of 182 MdNAC genes were differentially expressed during the stages of fruit growth and ripening. Sequence analysis indicates that these 13 MdNAC genes harbour distinct structures and potentially diverse functions. The expression of both MdNAC1a and MdNAC78 was repressed by ethylene and induced by 1-MCP during storage. MdNAC2, MdNAC26, MdNAC41, MdNAC57, MdNAC80, MdNAC91, MdNAC119 and MdNAC141 were up-regulated by ethylene and their transcription mirrored ethylene production rates during storage. MdNAC1, MdNAC16 and MdNAC32 did not respond to 1-MCP exposure. Additionally, the 13 MdNAC genes identified displayed differential tissue-specific expression patterns. These results suggest that NAC TFs play an important role in the regulation of apple development via both ethylene-dependent and -independent mechanisms.

Asymmetric Evolution and Expansion of the NAC Transcription Factor in Polyploidized Cotton

Polyploidy in Gossypium hirsutum conferred different properties from its diploid ancestors under the regulation of transcription factors. The NAC transcription factor is a plant-specific family that can be related to plant growth and development. So far, little is known about the NAC family in cotton. This study identified 495 NAC genes in three cotton species and investigated the evolution and expansion of different genome-derived NAC genes in cotton. We revealed 15 distinct NAC subfamilies in cotton. Different subfamilies had different gene proportions, expansion rate, gene loss rate, and orthologous exchange rate. Paleohexaploidization (35%) and cotton-specific decaploidy (32%) might have primarily led to the expansion of the NAC family in cotton. Half of duplication events in G. hirsutum were inherited from its diploid ancestor, and others might have occurred after interspecific hybridization. In addition, NAC genes in the At and Dt subgenomes displayed asymmetric molecular evolution, as evidenced by their different gene loss rates, orthologous exchange, evolutionary rates, and expression levels. The dominant duplication event was different during the cotton evolutionary history. Different genome-derived NACs might have interacted with each other, which ultimately resulted in morphogenetic evolution. This study delineated the expansion and evolutionary history of the NAC family in cotton and illustrated the different fates of NAC genes during polyploidization.

Bioinformatics and expression analysis of NAC transcription factor genes in Scutellaria baicalensis

Background: NAC, as a unique transcription factor to plants, plays important roles in multiple biological functions, such as regulation of plant growth and development, hormone levels, and responses to various kinds of stresses. However, there is a lack of research of NAC genes in Chinese herbs. Objective: The study aimed to evaluate the potential functions of NAC genes in Scutellaria baicalensis by bioinformatics and expression analysis, and provide evidence of the molecular regulation mechanism involved in flavonoid biosynthesis in S. baicalensis. Methods: The genes of NAC transcription factors in S. baicalensis were obtained from cDNA library and their functions were explored using bioinformatic methods. The NAC genes were screened from the cDNA library of S. baicalensis using BLAST comparison software. Then, the open reading frame (ORF) finder online tool was used to predict the full-length ORFs of NAC genes and their protein characteristics were explored by bioinformatic methods. The expression of NAC genes was then detected by quantitative polymerase chain reaction in different parts of S. baicalensis and different leaves treated by gibberellin GA3 treatment. Results: Six genes of NAC transcription factors were cloned, two of which had complete ORFs. NAC genes cloned in this study were mainly expressed in the flowers of S. baicalensis. The expression levels of NAC2, NAC3, NAC4, NAC5, NAC6 were increased firstly and then decreased gradually after 100 μM GA3 treatment. Meanwhile, some NACs and PAL2 in S. baicalensis showed strong correlation. Conclusion: This study suggested that NACs cloned in this study were mainly regulated the flavonoid biosynthesis in the flowers of S. baicalensis; NAC6 in S. baicalensis might be involved in the regulation of PAL2 transcription and affected the accumulation of flavonoids in the root of S. baicalensis. Our results provided a basis for further understanding the molecular regulation mechanism of flavonoid biosynthesis in S. baicalensis.

Research Article Characterization of Genetic Diversity and Linkage Disequilibrium of ZmNAC33 in Maize

The maize NAC gene, encoding a NAC domain transcription factor, plays vital roles in the growth process of maize under abiotic stresses. To investigate the response of ZmNAC33 to salinity stress, we analyzed the expression of the ZmNAC33 gene in roots and leaves of three-leaf stage seedlings among maize inbred lines. The result showed that the expression of ZmNAC33 was up-regulated in the salinity tolerant inbred line Ji853 and down-regulated in the salinity susceptible inbred line Chang7-2. The cDNA and the full sequence from maize inbred line Ji853 were amplified to analyze genetic structure. ZmNAC33 gene comprises three exons and two introns. We compared genetic diversity of ZmNAC33 among 69 elite maize inbred lines, a total of 144 sequence variants, including 113 SNPs and 31 Indels. Neutrality tests were negative selection by Tajima’s D and Fu and Li’s test. Analysis of polymorphism sites showed that at least 28 recombination’s have occurred. This finding provides insight into the development of breeding programs, germplasm management and association genetic studies.

An apple NAC transcription factor negatively regulates cold tolerance via CBF-dependent pathway

Cold stress is an adverse stimulus that affects plant growth and development, and the C-repeat binding factor (CBF) cold-regulatory cascade has been regarded as a master regulator in the plant response to cold stress. Here, we showed that a NAC transcription factor modulated low-temperature tolerance. MdNAC029/MdNAP, an apple NAC gene was isolated and its role in regulating cold tolerance was investigated. MdNAC029 was responsive to low-temperature treatment, and over-expression of MdNAC029 reduced cold tolerance in apple calli and Arabidopsis. Furthermore, EMSA assays and transient expression assays demonstrated that MdNAC029 directly repressed the expression of MdCBF1 and MdCBF4 by binding to their promoters. Taken together, our data suggest that MdNAC029 functions as a negative regulator in regulating plant cold tolerance in a CBF-dependent manner, providing a deeper understanding of NAC transcription-factor-mediated cold tolerance.

Ectopic Expression of Pumpkin NAC Transcription Factor CmNAC1 Improves Multiple Abiotic Stress Tolerance in Arabidopsis.

Drought, cold and salinity are the major environmental stresses that limit agricultural productivity. NAC transcription factors regulate the stress response in plants. Pumpkin (Cucurbita moschata) is an important cucurbit vegetable crop and it has strong resistance to abiotic stress; however, the biological functions of stress-related NAC genes in this crop are largely unknown. This study reports the function of CmNAC1, a stress-responsive pumpkin NAC domain protein. The CmNAC1-GFP fusion protein was transiently expressed in tobacco leaves for subcellular localization analysis, and we found that CmNAC1 is localized in the nucleus. Transactivation assay in yeast cells revealed that CmNAC1 functions as a transcription activator, and its transactivation domain is located in the C-terminus. CmNAC1 was ubiquitously expressed in different organs, and its transcript was induced by salinity, cold, dehydration, H2O2, and abscisic acid (ABA) treatment. Furthermore, the ectopic expression (EE) of CmNAC1 in Arabidopsis led to ABA hypersensitivity and enhanced tolerance to salinity, drought and cold stress. In addition, five ABA-responsive elements were enriched in CmNAC1 promoter. The CmNAC1-EE plants exhibited different root architecture, leaf morphology, and significantly high concentration of ABA compared with WT Arabidopsis under normal conditions. Our results indicated that CmNAC1 is a critical factor in ABA signaling pathways and it can be utilized in transgenic breeding to improve the abiotic stress tolerance of crops.

De novo RNA sequencing transcriptome of Rhododendron obtusum identified the early heat response genes involved in the transcriptional regulation of photosynthesis.

Rhododendron spp. is an important ornamental species that is widely cultivated for landscape worldwide. Heat stress is a major obstacle for its cultivation in south China. Previous studies on rhododendron principally focused on its physiological and biochemical processes, which are involved in a series of stress tolerance. However, molecular or genetic properties of rhododendron’s response to heat stress are still poorly understood. The phenotype and chlorophyll fluorescence kinetics parameters of four rhododendron cultivars were compared under normal or heat stress conditions, and a cultivar with highest heat tolerance, “Yanzhimi” (R. obtusum) was selected for transcriptome sequencing. A total of 325,429,240 high quality reads were obtained and assembled into 395,561 transcripts and 92,463 unigenes. Functional annotation showed that 38,724 unigenes had sequence similarity to known genes in at least one of the proteins or nucleotide databases used in this study. These 38,724 unigenes were categorized into 51 functional groups based on Gene Ontology classification and were blasted to 24 known cluster of orthologous groups. A total of 973 identified unigenes belonged to 57 transcription factor families, including the stress-related HSF, DREB, ZNF, and NAC genes. Photosynthesis was significantly enriched in the Kyoto Encyclopedia of Genes and Genomes pathway, and the changed expression pattern was illustrated. The key pathways and signaling components that contribute to heat tolerance in rhododendron were revealed. These results provide a potentially valuable resource that can be used for heat-tolerance breeding.

Expression patterns and promoter analyses of aluminum-responsive NAC genes suggest a possible growth regulation of rice mediated by aluminum, hormones and NAC transcription factors.

In acid soils, the solubilized form of aluminum, Al+3, decreases root growth and affects the development of most crops. However, like other toxic elements, Al can have hormetic effects on plant metabolism. Rice (Oryza sativa) is one of the most tolerant species to Al toxicity, and when this element is supplied at low doses, growth stimulation has been observed, which could be due to combined mechanisms that are partly triggered by NAC transcription factors. This protein family can regulate vital processes in plants, including growth, development, and response to environmental stimuli, whether biotic or abiotic. Under our experimental conditions, 200 μM Al stimulated root growth and the formation of tillers; it also caused differential expression of a set of NAC genes. The promoter regions of the genes regulated by Al were analyzed and the cis-acting elements that are potentially involved in the responses to different stimuli, including environmental stress, were identified. Through the Genevestigator platform, data on the expression of NAC genes were obtained by experimental condition, tissue, and vegetative stage. This is the first study on NAC genes where in vivo and in silico data are complementarily analyzed, relating the hormetic effect of Al on plant growth and gene expression with a possible interaction in the response to phytohormones in rice. These findings could help to elucidate the possible convergence between the signaling pathways mediated by phytohormones and the role of the NAC transcription factors in the regulation of growth mediated by low Al doses.

Six NAC transcription factors involved in response to TYLCV infection in resistant and susceptible tomato cultivars

NAC transcription factors (TFs) belong to plant-specific TFs, which have been identified in many plant species. The NAC TFs act as the nodes of a regulatory network in plant's response to abiotic and biotic stresses. Till now, response of tomato NAC TFs involved in Tomato yellow leaf curl virus (TYLCV) infection is unknown. In the present study, six NAC TFs were identified to respond to TYLCV infection in tomato. We observed that transcripts of four NAC genes (SlNAC20, SlNAC24, SlNAC47, and SlNAC61) were induced after TYLCV infection in resistant tomato cultivar. Virus-induced gene silencing analysis (VIGS) indicated that SlNAC61 played positive roles in response to TYLCV infection. Tomato NAC TFs were not only involved in defense regulation but in development and stress progress. These NAC TFs interacted with other proteins, including protein phosphatase and mitogen-activated protein kinase. Some defense response TFs, such as WRKY, TGA, MYB, NAC, could interact with NAC proteins by binding cis-elements in promoter regions of NAC TFs. These identified tomato NAC TFs cooperated with other TFs and proteins, indicating the complex response mechanism of described NAC TFs involved in TYLCV infection. The results will offer new evidence to further understand the NAC TFs involved in response to TYLCV infection in tomato.

The Glycine soja NAC transcription factor GsNAC019 mediates the regulation of plant alkaline tolerance and ABA sensitivity

Overexpression of Gshdz4 or GsNAC019 enhanced alkaline tolerance in transgenic Arabidopsis. We proved that Gshdz4 up-regulated both GsNAC019 and GsRD29B but GsNAC019 may repress the GsRD29B expression under alkaline stress. Wild soybean (Glycine soja) has a high tolerance to environmental challenges. It is a model species for dissecting the molecular mechanisms of salt-alkaline stresses. Although many NAC transcription factors play important roles in response to multiple abiotic stresses, such as salt, osmotic and cold, their mode of action in alkaline stress resistance is largely unknown. In our study, we identified a G. soja NAC gene, GsNAC019, which is a homolog of the Arabidopsis AtNAC019 gene. GsNAC019 was highly up-regulated by 50mM NaHCO3 treatment in the roots of wild soybean. Further investigation showed that a well-characterized transcription factor, Gshdz4 protein, bound the cis-acting element sequences (CAATA/TA), which are located in the promoter of the AtNAC019/GsNAC019 genes. Overexpression of Gshdz4 positively regulated AtNAC019 expression in transgenic Arabidopsis, implying that AtNAC019/GsNAC019 may be the target genes of Gshdz4. GsNAC019 was demonstrated to be a nuclear-localized protein in onion epidermal cells and possessed transactivation activity in yeast cells. Moreover, overexpression of GsNAC019 in Arabidopsis resulted in enhanced tolerance to alkaline stress at the seedling and mature stages, but reduced ABA sensitivity. The closest Arabidopsis homolog mutant plants of Gshdz4, GsNAC019 and GsRD29B containing athb40, atnac019 and atrd29b were sensitive to alkaline stress. Overexpression or the closest Arabidopsis homolog mutant plants of the GsNAC019 gene in Arabidopsis positively or negatively regulated the expression of stress-related genes, such as AHA2, RD29A/B and KIN1. Moreover, this mutation could phenotypically promoted or compromised plant growth under alkaline stress, implying that GsNAC019 may contribute to alkaline stress tolerance via the ABA signal transduction pathway and regulate expression of the downstream stress-related genes.

MiR3954 is a trigger of phasiRNAs that affects flowering time in citrus

In plant, a few 22-nt miRNAs direct cleavages of their targets and trigger the biogenesis of phased small interfering RNAs (phasiRNAs) in plant. In this study, we characterized a miRNA triggering phasiRNAs generation, miR3954, and explored its downstream target genes and potential function. Our results demonstrated that miR3954 showed specific expression in the flowers of citrus species, and it targeted a NAC transcription factor (Cs7g22460) and two non-coding RNA transcripts (lncRNAs, Cs1g09600 and Cs1g09635). The production of phasiRNAs was detected from transcripts targeted by miR3954, and was further verified in both sequencing data and transient expression experiments. PhasiRNAs derived from the two lncRNAs targeted not only miR3954-targeted NAC gene but also additional NAC homologous genes. No homologous genes of these two lncRNAs were found in plants other than citrus species, implying that this miR3954-lncRNAs-phasiRNAs-NAC pathway is likely citrus-specific. Transgenic analysis indicated that the miR3954-overexpressing lines showed decreased transcripts of lncRNA, elevated abundance of phasiRNAs and reduced expression of NAC genes. Interestingly, the overexpression of miR3954 leads to early flowering in citrus plants. In summary, our results illustrated a model of the regulatory network of miR3954-lncRNA-phasiRNAs-NAC, which may be functionally involved in flowering in citrus.

Sequence characterization and expression analysis of NAC genes from Betula platyphylla

The expression analysis of 21 BpNAC genes in stem, xylem from different growth season, and tension wood indicated that they might participate in xylem and tension wood development in birch. NAC transcription factors play important roles in the growth and development of plants. The NAC family has many members; however, the functions of the majority of them are unknown, especially in woody plants. In this study, to characterize the NAC members and explore NAC genes’ association with xylem development, 21 full-length NAC genes were identified in Betula platyphylla, a deciduous woody plant. Most of the 21 NAC proteins contain a complete NAC DNA-binding domain and a variable transcriptional regulation domain. Motif analysis showed that proteins within the same group mostly have similar motifs; however, there were no obvious similarities in gene structures among the identified BpNACs, based on exon/intron analysis. Cis-elements analysis indicated that promoters of the 21 BpNAC genes were enriched in ABRE and AC-box elements, suggesting that BpNAC genes might be related to ABA signal transduction pathways and xylem development. Quantitative real-time PCR analysis indicated that the 21 BpNACs were differentially expressed in the stem of B. platyphylla. In different stages of the growth season, BpNACs showed expression differences in the developing xylem. These genes also responded to artificial bending in tension wood and opposite wood, to varying degrees, and exhibited distinct expression patterns at different treatment times. The results indicated that these BpNAC genes might participate in tension wood development. Our study provided the basis for further functional investigations of BpNAC genes in birch.

Genome-wide identification, classification and expression analysis of NAC family of genes in sorghum [Sorghum bicolor (L.) Moench

NAC transcription factors are involved in many biological processes via regulation of downstream target gene expression and play essential roles in regulation of plant growth and improving plant tolerance to abiotic stress. NAC transcription factors have been studied in various species, but little information is available regarding these factors in sorghum. Genome-wide investigation of potentially abiotic stress related sorghum NAC-type genes was performed. A total of 145 non-redundant NAC genes (SbNAC1 –SbNAC145) were identified in the sorghum genome. These genes were distributed unevenly across the 10 chromosomes, and were divided into 16 groups based on sequence similarity. Gene structure analysis indicated that most SbNAC genes contained three exons and two introns, and had ten putative conserved motifs. Phylogenetic analysis indicated that the SbNAC genes with similar motif distributions were clustered into the same branch. Seven SbNAC genes, which were grouped into the stress-related subgroup, were isolated and have been confirmed to have transcriptional activity in yeast. SbNAC genes showed differential expression patterns over time in response to dehydration, salinity, cold, and phytohormone abscisic acid stress treatments, thus suggesting essential roles in plant responses to abiotic stress. In the germination stage, SbNAC56 overexpression transgenic lines exhibited significantly enhanced hypersensitivities to ABA, NaCl and d-Mannitol. This may infer that SbNAC56 may play essential roles in plants response to abiotic stresses in ABA dependent signaling pathway. Here, we present a comprehensive overview of the SbNAC genes and provide a foundation for future functional research regarding their biological roles in sorghum stress tolerance, even in the regulation of plant growth.

Overexpression of a peanut NAC gene, AhNAC4, confers enhanced drought tolerance in tobacco

NAC is one of the most abundant plant-specific groups of transcription factors, which play important roles in plant growth and development regulation, as well as in biotic and abiotic stress responses. In the present study, a stress-responsive NAC gene, AhNAC4, was isolated from a cDNA library of peanut (Arachis hypogaea L.) immature seeds, and characterized for its role in drought tolerance. AhNAC4 shared high amino acid similarity with NAC proteins belonging to the ATAF subfamily. The expression analysis indicated that AhNAC4 was highly induced by drought, salinity and ABA treatments. Transient expression analysis showed the AhNAC4-GFP fusion protein was exclusively localized in the nucleus of onion epidermal cells. Transactivation assays in yeast cells demonstrated that AhNAC4 functioned as a transcription activator and its C-terminus contained the activation domain. Overexpression of AhNAC4 confers enhanced drought tolerance in transgenic tobacco plants. The improved drought tolerance was associated with more stomatal closure and higher water use efficiency. Collectively, our results indicated that AhNAC4 functions as an important regulator in response to drought stress.

MiRNA mediated regulation of NAC transcription factors in plant development and environment stress response

NAC genes comprise one of the largest families of plant transcription regulators that are known to play crucial roles in various developmental processes and stress responses. Evolutionary expansion of the gene family in land plants probably added to the functional diversity of the gene family. The ongoing research has analyzed the differential expression patterns of the NAC transcription factors under various stresses for determining their plausible role during adaptive stress response in plants. However, the complex molecular mechanism regulating NAC gene expression and function is still elusive. The discovery of miRNAs, as a novel class of regulatory factors, has shed new light on the regulatory mechanisms that define the functional domains of the transcription factors. In this context studies on miRNA-mediated regulation of NAC gene expression in plant development have provided critical evidence for multi-layered control of the transcription factors. The review describes the divergent role of NAC transcription factors, which were initially thought to be only involved in vasculature development in plants. The structural features of the NAC transcription factors and the evolution of the gene family have also been discussed. Special focus is placed on the regulation of NAC-TFs by miRNAs to understand the developmental networks operating in the plants in response to abiotic stress and hormone cues.