Genome-wide analysis of the NAC transcription factor family and their expression during the development and ripening of the Fragaria × ananassa fruits

Overexpression of a Fragaria vesca NAM, ATAF, and CUC (NAC) Transcription Factor Gene (FvNAC29) Increases Salt and Cold Tolerance in Arabidopsis thaliana

The NAC (NAM, ATAF1/2, CUC2) family of transcription factors (TFs) is a vital transcription factor family of plants. It controls multiple parts of plant development, tissue formation, and abiotic stress response. We cloned the FvNAC29 gene from Fragaria vesca (a diploid strawberry) for this research. There is a conserved NAM structural domain in the FvNAC29 protein. The highest homology between FvNAC29 and PaNAC1 was found by phylogenetic tree analysis. Subcellular localization revealed that FvNAC29 is localized onto the nucleus. Compared to other tissues, the expression level of FvNAC29 was higher in young leaves and roots. In addition, Arabidopsis plants overexpressing FvNAC29 had higher cold and high-salinity tolerance than the wild type (WT) and unloaded line with empty vector (UL). The proline and chlorophyll contents of transgenic Arabidopsis plants, along with the activities of the antioxidant enzymes like catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) under 200 mM NaCl treatment or -8 °C treatment, were higher than those activities of the control. Meanwhile, malondialdehyde (MDA) and the reactive oxygen species (ROS) content were higher in the WT and UL lines. FvNAC29 improves transgenic plant resistance to cold and salt stress by regulating the expression levels of AtRD29a, AtCCA1, AtP5CS1, and AtSnRK2.4. It also improves the potential to tolerate cold stress by positively regulating the expression levels of AtCBF1, AtCBF4, AtCOR15a, and AtCOR47. These findings suggest that FvNAC29 may be related to the processes and the molecular mechanisms of F. vesca response to high-salinity stress and LT stress, providing a comprehensive understanding of the NAC TFs.

Comprehensive Analysis of NAC Transcription Factors Reveals Their Evolution in Malvales and Functional Characterization of AsNAC019 and AsNAC098 in Aquilaria sinensis

NAC is a class of plant-specific transcription factors that are widely involved in the growth, development and (a)biotic stress response of plants. However, their molecular evolution has not been extensively studied in Malvales, especially in Aquilaria sinensis, a commercial and horticultural crop that produces an aromatic resin named agarwood. In this study, 1502 members of the NAC gene family were identified from the genomes of nine species from Malvales and three model plants. The macroevolutionary analysis revealed that whole genome duplication (WGD) and dispersed duplication (DSD) have shaped the current architectural structure of NAC gene families in Malvales plants. Then, 111 NAC genes were systemically characterized in A. sinensis. The phylogenetic analysis suggests that NAC genes in A. sinensis can be classified into 16 known clusters and four new subfamilies, with each subfamily presenting similar gene structures and conserved motifs. RNA-seq analysis showed that AsNACs presents a broad transcriptional response to the agarwood inducer. The expression patterns of 15 AsNACs in A. sinensis after injury treatment indicated that AsNAC019 and AsNAC098 were positively correlated with the expression patterns of four polyketide synthase (PKS) genes. Additionally, AsNAC019 and AsNAC098 were also found to bind with the AsPKS07 promoter and activate its transcription. This comprehensive analysis provides valuable insights into the molecular evolution of the NAC gene family in Malvales plants and highlights the potential mechanisms of AsNACs for regulating secondary metabolite biosynthesis in A. sinensis, especially for the biosynthesis of 2-(2-phenyl) chromones in agarwood.

The NAC Transcription Factor PgNAC41-2 Gene Involved in the Regulation of Ginsenoside Biosynthesis in Panax ginseng

Ginseng (Panax ginseng C.A. Meyer) is a perennial herb of the Araliaceae family, a traditional and valuable Chinese herb in China. The main active component of ginseng is ginsenoside. The NAC transcription factors belong to a large family of plant-specific transcription factors, which are involved in growth and development, stress response and secondary metabolism. In this study, we mapped the NAC gene family on 24 pairs of ginseng chromosomes and found numerous gene replications in the genome. The NAC gene PgNAC41-2, found to be highly related to ginsenoside synthesis, was specifically screened. The phylogeny and expression pattern of the PgNAC41-2 gene were analyzed, along with the derived protein sequence, and a structure model was generated. Furthermore, the PgNAC41-2 gene was cloned and overexpressed by a Rhizobium rhizogenes mediated method, using ginseng petioles as receptor material. The saponin content of the transformed material was analyzed to verify the function of the NAC transcription factor in ginseng. Our results indicate that the PgNAC41-2 gene positively regulates the biosynthesis of saponins.

Marker-Assisted Selection in Breeding for Fruit Trait Improvement: A Review

Breeding fruit species is time-consuming and expensive. With few exceptions, trees are likely the worst species to work with in terms of genetics and breeding. Most are characterized by large trees, long juvenile periods, and intensive agricultural practice, and environmental variability plays an important role in the heritability evaluations of every single important trait. Although vegetative propagation allows for the production of a significant number of clonal replicates for the evaluation of environmental effects and genotype × environment interactions, the spaces required for plant cultivation and the intensity of work necessary for phenotypic surveys slow down the work of researchers. Fruit breeders are very often interested in fruit traits: size, weight, sugar and acid content, ripening time, fruit storability, and post-harvest practices, among other traits relevant to each individual species. The translation of trait loci and whole-genome sequences into diagnostic genetic markers that are effective and affordable for use by breeders, who must choose genetically superior parents and subsequently choose genetically superior individuals among their progeny, is one of the most difficult tasks still facing tree fruit geneticists. The availability of updated sequencing techniques and powerful software tools offered the opportunity to mine tens of fruit genomes to find out sequence variants potentially useful as molecular markers. This review is devoted to analysing what has been the role of molecular markers in assisting breeders in selection processes, with an emphasis on the fruit traits of the most important fruit crops for which examples of trustworthy molecular markers have been developed, such as the MDo.chr9.4 marker for red skin colour in apples, the CCD4-based marker CPRFC1, and LG3_13.146 marker for flesh colour in peaches, papayas, and cherries, respectively.

FaMYB123 interacts with FabHLH3 to regulate the late steps of anthocyanin and flavonol biosynthesis during ripening

In this work, we identified and functionally characterized the strawberry (Fragaria × ananassa) R2R3 MYB transcription factor FaMYB123. As in most genes associated with organoleptic properties of ripe fruit, FaMYB123 expression is ripening-related, receptacle-specific, and antagonistically regulated by ABA and auxin. Knockdown of FaMYB123 expression by RNAi in ripe strawberry fruit receptacles downregulated the expression of enzymes involved in the late steps of anthocyanin/flavonoid biosynthesis. Transgenic fruits showed a parallel decrease in the contents of total anthocyanin and flavonoid, especially malonyl derivatives of pelargonidin and cyanidins. The decrease was concomitant with accumulation of proanthocyanin, propelargonidins, and other condensed tannins associated mainly with green receptacles. Potential coregulation between FaMYB123 and FaMYB10, which may act on different sets of genes for the enzymes involved in anthocyanin production, was explored. FaMYB123 and FabHLH3 were found to interact and to be involved in the transcriptional activation of FaMT1, a gene responsible for the malonylation of anthocyanin components during ripening. Taken together, these results demonstrate that FaMYB123 regulates the late steps of the flavonoid pathway in a specific manner. In this study, a new function for an R2R3 MYB transcription factor, regulating the expression of a gene that encodes a malonyltransferase, has been elucidated.

The NAC transcription factors play core roles in flowering and ripening fundamental to fruit yield and quality

Fruits are derived from flowers and play an important role in human food, nutrition, and health. In general, flowers determine the crop yield, and ripening affects the fruit quality. Although transcription factors (TFs) only account for a small part of plant transcriptomes, they control the global gene expression and regulation. The plant-specific NAC (NAM, ATAF, and CUC) TFs constitute a large family evolving concurrently with the transition of both aquatic-to-terrestrial plants and vegetative-to-reproductive growth. Thus, NACs play an important role in fruit yield and quality by determining shoot apical meristem (SAM) inflorescence and controlling ripening. The present review focuses on the various properties of NACs together with their function and regulation in flower formation and fruit ripening. Hitherto, we have a better understanding of the molecular mechanisms of NACs in ripening through abscisic acid (ABA) and ethylene (ETH), but how NACs regulate the expression of the inflorescence formation-related genes is largely unknown. In the future, we should focus on the analysis of NAC redundancy and identify the pivotal regulators of flowering and ripening. NACs are potentially vital manipulation targets for improving fruit quantity and quality.

Transcriptome-wide identification of NAC (no apical meristem/Arabidopsis transcription activation factor/cup-shaped cotyledon) transcription factors potentially involved in salt stress response in garlic

Soil salinity has been an increasing problem worldwide endangering crop production and human food security. It is an ideal strategy to excavate stress resistant genes and develop salt tolerant crops. NAC (no apical meristem/Arabidopsis transcription activation factor/cup-shaped cotyledon) transcription factors have been demonstrated to be involved in salt stress response. However, relevant studies have not been observed in garlic, an important vegetable consumed in the world. In this study, a total of 46 AsNAC genes encoding NAC proteins were identified in garlic plant by transcriptome data. Phylogenetic analysis showed that the examined AsNAC proteins were clustered into 14 subgroups. Motif discovery revealed that the conserved domain region was mainly composed of five conserved subdomains. Most of the genes selected could be induced by salt stress in different tissues, indicating a potential role in salt stress response. Further studies may focus on the molecular mechanisms of the AsNAC genes in salt stress response. The results of the current work provided valuable resources for researchers aimed at developing salt tolerant crops.

The PavNAC56 transcription factor positively regulates fruit ripening and softening in sweet cherry (Prunus avium)

The rapid softening of sweet cherry fruits during ripening results in the deterioration of fruit quality. However, few genes related to sweet cherry fruit ripening and softening have been identified, and the molecular regulatory mechanisms underlying this process are poorly understood. Here, we identified and functionally characterized PavNAC56, a NAC transcription factor that positively regulates sweet cherry fruit ripening and softening. Gene expression analyses showed that PavNAC56 was specifically and abundantly expressed in the fruit, and its transcript levels increased in response to abscisic acid (ABA). A subcellular localization analysis revealed that PavNAC56 is a nucleus-localized protein. Virus-induced gene silencing of PavNAC56 inhibited fruit ripening, enhanced fruit firmness, decreased the contents of ABA, anthocyanins, and soluble solids, and down-regulated several fruit ripening-related genes. Yeast one-hybrid and dual-luciferase assays showed that PavNAC56 directly binds to the promoters of several genes related to cell wall metabolism (PavPG2, PavEXPA4, PavPL18, and PavCEL8) and activates their expression. Overall, our findings show that PavNAC56 plays an indispensable role in controlling the ripening and softening of sweet cherry fruit and provides new insights into the regulatory mechanisms by which NAC transcription factors affect nonclimacteric fruit ripening and softening.

Insights into transcription factors controlling strawberry fruit development and ripening

Fruit ripening is a highly regulated and complex process involving a series of physiological and biochemical changes aiming to maximize fruit organoleptic traits to attract herbivores, maximizing therefore seed dispersal. Furthermore, this process is of key importance for fruit quality and therefore consumer acceptance. In fleshy fruits, ripening involves an alteration in color, in the content of sugars, organic acids and secondary metabolites, such as volatile compounds, which influence flavor and aroma, and the remodeling of cell walls, resulting in the softening of the fruit. The mechanisms underlying these processes rely on the action of phytohormones, transcription factors and epigenetic modifications. Strawberry fruit is considered a model of non-climacteric species, as its ripening is mainly controlled by abscisic acid. Besides the role of phytohormones in the regulation of strawberry fruit ripening, a number of transcription factors have been identified as important regulators of these processes to date. In this review, we present a comprehensive overview of the current knowledge on the role of transcription factors in the regulation of strawberry fruit ripening, as well as in compiling candidate regulators that might play an important role but that have not been functionally studied to date.

Insights into Four NAC Transcription Factors Involved in Grain Development and in Response to Moderate Heat in the Triticeae Tribe

NAC (NAM (no apical meristem)−ATAF (Arabidopsis transcription activation factor)−CUC (cup-shaped cotyledons)) are among the largest transcription factor families in plants, involved in a plethora of physiological mechanisms. This study focused on four NAC genes previously identified in bread wheat as specifically grain-expressed which could be considered as candidate genes for yield improvement under climate changes. Using in silico analyses, the Triticum aestivum “Grain-NAC” (TaGNAC) orthologs in 14 cereal species were identified. A conserved protein motif was identified only in Triticeae. The expression of TaGNAC and einkorn TmGNAC was studied in response to moderate heat stress during grain development and showed a similar expression pattern that is accelerated during cell division stages under heat stress. A conserved structure was found in the promoter of the Triticeae GNAC orthologs, which is absent in the other Poaceae species. A specific model of promoter structure in Triticeae was proposed, based on the presence of key cis-elements involved in the regulation of seed development, hormonal regulation and response to biotic and abiotic stresses. In conclusion, GNAC genes could play a central role in the regulation of grain development in the Triticeae tribe, particularly in the accumulation of storage proteins, as well as in response to heat stress and could be used as candidate genes for breeding.

Signal transduction in non-climacteric fruit ripening

Fleshy fruit ripening involves changes in numerous cellular processes and metabolic pathways, resulting from the coordinated actions of diverse classes of structural and regulatory proteins. These include enzymes, transporters and complex signal transduction systems. Many aspects of the signaling machinery that orchestrates the ripening of climacteric fruits, such as tomato (Solanum lycopersicum), have been elucidated, but less is known about analogous processes in non-climacteric fruits. The latter include strawberry (Fragaria x ananassa) and grape (Vitis vinifera), both of which are used as non-climacteric fruit experimental model systems, although they originate from different organs: the grape berry is a true fruit derived from the ovary, while strawberry is an accessory fruit that is derived from the floral receptacle. In this article, we summarize insights into the signal transduction events involved in strawberry and grape berry ripening. We highlight the mechanisms underlying non-climacteric fruit ripening, the multiple primary signals and their integrated action, individual signaling components, pathways and their crosstalk, as well as the associated transcription factors and their signaling output.

NAC Transcription Factor Family Regulation of Fruit Ripening and Quality: A Review

The NAC transcription factor (TF) family is one of the largest plant-specific TF families and its members are involved in the regulation of many vital biological processes during plant growth and development. Recent studies have found that NAC TFs play important roles during the ripening of fleshy fruits and the development of quality attributes. This review focuses on the advances in our understanding of the function of NAC TFs in different fruits and their involvement in the biosynthesis and signal transduction of plant hormones, fruit textural changes, color transformation, accumulation of flavor compounds, seed development and fruit senescence. We discuss the theoretical basis and potential regulatory models for NAC TFs action and provide a comprehensive view of their multiple roles in modulating different aspects of fruit ripening and quality.

Drought Stress Mitigating Morphological, Physiological, Biochemical, and Molecular Responses of Guava (Psidium guajava L.) Cultivars

Guava (Psidium guajava L.), a major fruit crop of the sub-tropical region, is facing a production decline due to drought stress. Morphophysiological responses to drought stress and underlying transcriptional regulations in guava are, largely, unknown. This study evaluated the drought stress tolerance of two guava cultivars, viz. "Gola" and "Surahi," at morphological and physiological levels regulated differentially by ESTs (Expressed Sequence Tags). The treatments comprises three moisture regimes, viz. T_o = 100% (control), T₁ = 75%, and T₂ = 50% of field capacity. There was an overall decrease in both morphological and physiological attributes of studied guava cultivars in response to drought stress. Nonetheless, the water use efficiency of the "Surahi" cultivar increased (41.86%) speculating its higher drought tolerance based on enhanced peroxidase (402%) and catalase (170.21%) activities under 50% field capacity (T₂). Moreover, higher proline and flavonoid contents reinforced drought stress retaliation of the "Surahi" cultivar. The differential expression of a significant number of ESTs in "Surahi" (234) as compared to "Gola" (117) cultivar, somehow, regulated its cellular, biological, and molecular functions to strengthen morphophysiological attributes against drought stress as indicated by the upregulation of ESTs related to peroxidase, sucrose synthase (SUS), alcohol dehydrogenase (ADH), and ubiquitin at morphological, biochemical, and physiological levels. In conclusion, the drought stress acclimation of pear-shaped guava cultivar "Surahi" is due to the increased activities of peroxidase (POD) and catalase (CAT) complimented by the upregulation of related ESTs.

Roles of abscisic acid in regulating ripening and quality of strawberry, a model non-climacteric fruit

Abscisic acid (ABA) is a dominant regulator of ripening and quality in non-climacteric fruits. Strawberry is regarded as a model non-climacteric fruit due to its extensive genetic studies and proven suitability for transgenic approaches to understanding gene function. Strawberry research has contributed to studies on color, flavor development, and fruit softening, and in recent years ABA has been established as a core regulator of strawberry fruit ripening, whereas ethylene plays this role in climacteric fruits. Despite this major difference, several components of the interacting genetic regulatory network in strawberry, such as MADS-box and NAC transcription factors, are similar to those that operate in climacteric fruit. In this review, we summarize recent advances in understanding the role of ABA biosynthesis and signaling and the regulatory network of transcription factors and other phytohormones in strawberry fruit ripening. In addition to providing an update on its ripening, we discuss how strawberry research has helped generate a broader and more comprehensive understanding of the mechanism of non-climacteric fruit ripening and focus attention on the use of strawberry as a model platform for ripening studies.

Roles of abscisic acid in regulating ripening and quality of strawberry, a model non-climacteric fruit

Abscisic acid (ABA) is a dominant regulator of ripening and quality in non-climacteric fruits. Strawberry is regarded as a model non-climacteric fruit due to its extensive genetic studies and proven suitability for transgenic approaches to understanding gene function. Strawberry research has contributed to studies on color, flavor development, and fruit softening, and in recent years ABA has been established as a core regulator of strawberry fruit ripening, whereas ethylene plays this role in climacteric fruits. Despite this major difference, several components of the interacting genetic regulatory network in strawberry, such as MADS-box and NAC transcription factors, are similar to those that operate in climacteric fruit. In this review, we summarize recent advances in understanding the role of ABA biosynthesis and signaling and the regulatory network of transcription factors and other phytohormones in strawberry fruit ripening. In addition to providing an update on its ripening, we discuss how strawberry research has helped generate a broader and more comprehensive understanding of the mechanism of non-climacteric fruit ripening and focus attention on the use of strawberry as a model platform for ripening studies.

The Gillenia trifoliata genome reveals dynamics correlated with growth and reproduction in Rosaceae

The Rosaceae family has striking phenotypic diversity and high syntenic conservation. Gillenia trifoliata is sister species to the Maleae tribe of apple and ~1000 other species. Gillenia has many putative ancestral features, such as herb/sub-shrub habit, dry fruit-bearing and nine base chromosomes. This coalescence of ancestral characters in a phylogenetically important species, positions Gillenia as a 'rosetta stone' for translational science within Rosaceae. We present genomic and phenological resources to facilitate the use of Gillenia for this purpose. The Gillenia genome is the first fully annotated chromosome-level assembly with an ancestral genome complement (x = 9), and with it we developed an improved model of the Rosaceae ancestral genome. MADS and NAC gene family analyses revealed genome dynamics correlated with growth and reproduction and we demonstrate how Gillenia can be a negative control for studying fleshy fruit development in Rosaceae.

Comprehensive Analyses of NAC Transcription Factor Family in Almond (Prunus dulcis) and Their Differential Gene Expression during Fruit Development

As plant specific transcription factors, NAC (NAM, ATAF1/2, CUC2) domain is involved in the plant development and stress responses. Due to the vitality of NAC gene family, BLASTp was performed to identify NAC genes in almond (Prunus dulcis). Further, phylogenetic and syntenic analyses were performed to determine the homology and evolutionary relationship. Gene duplication, gene structure, motif, subcellular localization, and cis-regulatory analyses were performed to assess the function of PdNAC. Whereas RNA-seq analysis was performed to determine the differential expression of PdNAC in fruits at various developmental stages. We identified 106 NAC genes in P. dulcis genome and were renamed according to their chromosomal distribution. Phylogenetic analysis in both P. dulcis and Arabidopsis thaliana revealed the presence of 14 subfamilies. Motif and gene structure followed a pattern according to the PdNAC position in phylogenetic subfamilies. Majority of NAC are localized in the nucleus and have ABA-responsive elements in the upstream region of PdNAC. Differential gene expression analyses revealed one and six PdNAC that were up and down-regulated, respectively, at all development stages. This study provides insights into the structure and function of PdNAC along with their role in the fruit development to enhance an understanding of NAC in P. dulcis.

Genome-wide identification and comprehensive analysis of the NAC transcription factor family in sunflower during salt and drought stress

The NAC (NAM, ATAF1/2, and CUC2), is a large family of plant-specific transcription factors (TFs) that exert crucial regulatory roles in various physiological processes and abiotic stresses. There is scanty information on the role of the NAC family in sunflower (Helianthus annuus L.). In this study, we conducted a genome-wide survey and expression analysis of the NAC family in sunflower. A total of 150 HaNACs were identified in sunflower. Phylogenetic analysis to compare HaNACs with Arabidopsis NACs generated 15 clusters. Among them, eight membrane-bound NAC TFs with transmembrane helixes were found (designated as NTLs), which were suggested to be localized in the membrane and transferred to the nucleus through proteolysis. Notably, 12 HaNACs were potentially regulated via miR164 cleavage or translational inhibition. By analyzing RNA-seq data from Sequence Read Archive (SRA), the expression of HaNACs showed tissue specificity and strong response to drought stress. Additionally, phylogenetic analysis of 150 HaNACs with the previously reported NACs related to abiotic stress revealed that 75% of the abiotic stress-related NACs were clustered into the SNAC (abiotic stress-related NAC) group, and only 25% were in the Non-SNAC group. qRT-PCR further demonstrated that about 75% of the HaNACs in the SNAC subgroup were induced by salt and drought stress, and the expression of some HaNACs showed tissue specificity. These findings provide valuable information that can deepen the understanding of how NAC TFs in sunflower respond to abiotic stress.

MicroRNAs and Transcripts Associated with an Early Ripening Mutant of Pomelo (Citrus grandis Osbeck)

'Liuyuezaoyou' is an early-ripening cultivar selected from a bud mutation of Citrus grandis Osbeck 'Guanximiyou'. They were designated here as MT and WT, respectively. The fruit of MT matures about 45 days earlier than WT, which was accompanied by significant changes in key phytohormones, sugar compounds and organic acids. Recent studies have showed that microRNAs (miRNAs) play an important role in regulation of fruit ripening process. The aim of this study was to compare MT fruits with WT ones to uncover if miRNAs were implicated in the ripening of C. grandis. Fruits of both WT and MT at four developmental stages were analyzed using high-throughput sequencing and RT-PCR. Several independent miRNA libraries were constructed and sequenced. A total of 747 known miRNAs were identified and 99 novel miRNAs were predicted across all libraries. The novel miRNAs were found to have hairpin structures and possess star sequences. These results showed that transcriptome and miRNAs are substantially involved in a complex and comprehensive network in regulation of fruit ripening of this species. Further analysis of the network model revealed intricate interactions of miRNAs with mRNAs during the fleshy fruit ripening process. Several identified miRNAs have potential targets. These include auxin-responsive protein IAA9, sucrose synthase 3, V-type proton ATPase, NCED1 (ABA biosynthesis) and PL1/5 (pectate lyase genes), as well as NAC100 putative coordinated regulation networks, whose interactions with respective miRNAs may contribute significantly to fruit ripening of C. grandis.

Genome-wide comparative analyses of GATA transcription factors among seven Populus genomes

GATA transcription factors (TFs) are widespread eukaryotic regulators whose DNA-binding domain is a class IV zinc finger motif (CX2CX17-20CX2C) followed by a basic region. We identified 262 GATA genes (389 GATA TFs) from seven Populus genomes using the pipeline of GATA-TFDB. Alternative splicing forms of Populus GATA genes exhibit dynamics of GATA gene structures including partial or full loss of GATA domain and additional domains. Subfamily III of Populus GATA genes display lack CCT and/or TIFY domains. 21 Populus GATA gene clusters (PCs) were defined in the phylogenetic tree of GATA domains, suggesting the possibility of subfunctionalization and neofunctionalization. Expression analysis of Populus GATA genes identified the five PCs displaying tissue-specific expression, providing the clues of their biological functions. Amino acid patterns of Populus GATA motifs display well conserved manner of Populus GATA genes. The five Populus GATA genes were predicted as membrane-bound GATA TFs. Biased chromosomal distributions of GATA genes of three Populus species. Our comparative analysis approaches of the Populus GATA genes will be a cornerstone to understand various plant TF characteristics including evolutionary insights.

Transgene CpNAC68 from Wintersweet (Chimonanthus praecox) Improves Arabidopsis Survival of Multiple Abiotic Stresses

The NAC (NAM, ATAFs, CUC) family of transcription factors (TFs) play a pivotal role in regulating all processes of the growth and development of plants, as well as responses to biotic and abiotic stresses. Yet, the functions of NACs from non-model plant species remains largely uncharacterized. Here, we characterized the stress-responsive effects of a NAC gene isolated from wintersweet, an ornamental woody plant that blooms in winter when temperatures are low. CpNAC68 is clustered in the NAM subfamily. Subcellular localization and transcriptional activity assays demonstrated a nuclear protein that has transcription activator activities. qRT-PCR analyses revealed that CpNAC68 was ubiquitously expressed in old flowers and leaves. Additionally, the expression of CpNAC68 is induced by disparate abiotic stresses and hormone treatments, including drought, heat, cold, salinity, GA, JA, and SA. Ectopic overexpression of CpNAC68 in Arabidopsis thaliana enhanced the tolerance of transgenic plants to cold, heat, salinity, and osmotic stress, yet had no effect on growth and development. The survival rate and chlorophyll amounts following stress treatments were significantly higher than wild type Arabidopsis, and were accompanied by lower electrolyte leakage and malondialdehyde (MDA) amounts. In conclusion, our study demonstrates that CpNAC68 can be used as a tool to enhance plant tolerance to multiple stresses, suggesting a role in abiotic stress tolerance in wintersweet.

The NAC transcription factor FaRIF controls fruit ripening in strawberry

In contrast to climacteric fruits such as tomato, the knowledge on key regulatory genes controlling the ripening of strawberry, a nonclimacteric fruit, is still limited. NAC transcription factors (TFs) mediate different developmental processes in plants. Here, we identified and characterized Ripening Inducing Factor (FaRIF), a NAC TF that is highly expressed and induced in strawberry receptacles during ripening. Functional analyses based on stable transgenic lines aimed at silencing FaRIF by RNA interference, either from a constitutive promoter or the ripe receptacle-specific EXP2 promoter, as well as overexpression lines showed that FaRIF controls critical ripening-related processes such as fruit softening and pigment and sugar accumulation. Physiological, metabolome, and transcriptome analyses of receptacles of FaRIF-silenced and overexpression lines point to FaRIF as a key regulator of strawberry fruit ripening from early developmental stages, controlling abscisic acid biosynthesis and signaling, cell-wall degradation, and modification, the phenylpropanoid pathway, volatiles production, and the balance of the aerobic/anaerobic metabolism. FaRIF is therefore a target to be modified/edited to control the quality of strawberry fruits.

The interplay between ABA/ethylene and NAC TFs in tomato fruit ripening: a review

This review contains functional roles of NAC transcription factors in the transcriptional regulation of ripening in tomato fruit, describes the interplay between ABA/ethylene and NAC TFs in tomato fruit ripening. Fruit ripening is regulated by a complex network of transcription factors (TFs) and genetic regulators in response to endogenous hormones and external signals. Studying the regulation of fruit ripening has important significance for controlling fruit quality, enhancing nutritional value, improving storage conditions and extending shelf-life. Plant-specific NAC (named after no apical meristem (NAM), Arabidopsis transcription activator factor 1/2 (ATAF1/2) and Cup-shaped cotyledon (CUC2)) TFs play essential roles in plant development, ripening and stress responses. In this review, we summarize the recent progress on the regulation of NAC TFs in fruit ripening, discuss the interactions between NAC and other factors in controlling fruit development and ripening, and emphasize how NAC TFs are involved in tomato fruit ripening through the ethylene and abscisic acid (ABA) pathways. The signaling network regulating ripening is complex, and both hormones and individual TFs can affect the status or activity of other network participants, which can alter the overall ripening network regulation, including response signals and fruit ripening. Our review helps in the systematic understanding of the regulation of NAC TFs involved in fruit ripening and provides a basis for the development or establishment of complex ripening regulatory network models.

The NAC side of the fruit: tuning of fruit development and maturation

Fruits and seeds resulting from fertilization of flowers, represent an incredible evolutionary advantage in angiosperms and have seen them become a critical element in our food supply.Many studies have been conducted to reveal how fruit matures while protecting growing seeds and ensuring their dispersal. As result, several transcription factors involved in fruit maturation and senescence have been isolated both in model and crop plants. These regulators modulate several cellular processes that occur during fruit ripening such as chlorophyll breakdown, tissue softening, carbohydrates and pigments accumulation.The NAC superfamily of transcription factors is known to be involved in almost all these aspects of fruit development and maturation. In this review, we summarise the current knowledge regarding NACs that modulate fruit ripening in model species (Arabidopsis thaliana and Solanum lycopersicum) and in crops of commercial interest (Oryza sativa, Malus domestica, Fragaria genus, Citrus sinensis and Musa acuminata).

Comparative transcriptome and metabolome analyses of two strawberry cultivars with different storability

Postharvest storability is an important trait for breeding strawberry (Fragaria × ananassa Duch.). We evaluated the postharvest fruit quality of five strawberry cultivars (‘Durihyang’, ‘Kingsberry’, ‘Maehyang’, ‘Seolhyang’, and ‘Sunnyberry’) and identified differences in their fruit ripening during the transition from the big-green to fully-red stage between two cultivars with the highest (‘Sunnyberry’) and lowest (‘Kingsberry’) storability, using comparative transcriptome and -metabolome analysis. The differentially expressed genes revealed transcriptome changes related to anthocyanin biosynthesis and cell walls. Consistently, the metabolites of both cultivars showed general changes during ripening along with cultivar-specific characteristics in sugar and amino acid profiles. To identify the genes responsible for storability differences, we surveyed the expression of transcription factors, and found that the expression levels of WRKY31, WRKY70, and NAC83 correlated with delayed senescence and increased storability. Among them, the expression levels of NAC83, and its downstream target genes, in the five cultivars suggested that NAC83 expression can be used to predict postharvest strawberry fruit storability.

Identification, characterization and functional differentiation of the NAC gene family and its roles in response to cold stress in ginseng, Panax ginseng C.A. Meyer

The NAC gene family is one of the important plant-specific transcription factor families involved in variety of physiological processes. It has been found in several plant species; however, little is known about the gene family in ginseng, Panax ginseng C.A. Meyer. Here we report identification and systematic analysis of this gene family in ginseng. A total of 89 NAC genes, designated PgNAC01 to PgNAC89, are identified. These genes are alternatively spliced into 251 transcripts at fruiting stage of a four-year-old ginseng plant. The genes of this gene family have five conserved motifs and are clustered into 11 subfamilies, all of which are shared with the genes of the NAC gene families identified in the dicot and monocot model plant species, Arabidopsis and rice. This result indicates that the PgNAC gene family is an ancient and evolutionarily inactive gene family. Gene ontology (GO) analysis shows that the functions of the PgNAC gene family have been substantially differentiated; nevertheless, over 86% the PgNAC transcripts remain functionally correlated. Finally, five of the PgNAC genes, PgNAC05-2, PgNAC41-2, PgNAC48, PgNAC56-1, and PgNAC59, are identified to be involved in plant response to cold stress, suggesting that this gene family plays roles in response to cold stress in ginseng. These results, therefore, provide new insights into functional differentiation and evolution of a gene family in plants and gene resources necessary to comprehensively determine the functions of the PgNAC gene family in response to cold and other abiotic stresses in ginseng.

High-density genetic linkage-map construction of hawthorn and QTL mapping for important fruit traits

Few reports exist on QTL mapping of the important economic traits of hawthorn. We hybridized the cultivars ‘Shandongdamianqiu’ (female parent) and ‘Xinbinruanzi’ (male parent), and 130 F₁ individuals and the two parents were used for RAD-seq, SNP development, and high-density linkage map construction. Three genetic maps were obtained, one for each of the parents and an integrated one. In these three maps, 17 linkage groups were constructed. The female and male parent maps contained 2657 and 4088 SNP markers, respectively, and had genetic distances of 2689.65 and 2558.41 cM, respectively, whereas the integrated map was 2470.02 cM, and contained 6,384 SNP markers. QTL mapping based on six agronomic traits, namely fruit transverse diameter, vertical diameter, single fruit weight, pericarp brittleness, pericarp puncture hardness, and average sarcocarp firmness were conducted, and 25 QTLs were detected in seven linkage groups. Explained phenotypic variation rate ranged from 17.7% to 35%. This genetic map contains the largest number of molecular markers ever obtained from hawthorn and will provide an important future reference for fine QTL mapping of economic traits and molecular assisted selection of hawthorn.

Identification and Expression Analysis of the NAC Gene Family in Coffea canephora

The NAC gene family is one of the largest families of transcriptional regulators in plants, and it plays important roles in the regulation of growth and development as well as in stress responses. Genome-wide analyses have been performed in diverse plant species, but there is still no systematic analysis of the NAC genes of Coffea canephora Pierre ex A. Froehner. In this study, we identified 63 NAC genes from the genome of C. canephora. The basic features and comparison analysis indicated that the NAC gene members increased via duplication events during the evolution of the plant. Phylogenetic analysis divided the NAC proteins from C. canephora, Arabidopsis and rice into 16 subgroups. Analysis of the expression patterns of CocNACs under cold stress and coffee bean development indicated that 38 CocNACs were differentially expressed under cold stress; six genes may play important roles in the process of cold acclimation, and four genes among 54 CocNACs showing a variety of expression patterns during different developmental stages of coffee beans may be positively related to the bean development. This study can expand our understanding of the functions of the CocNAC gene family in cold responses and bean development, thereby potentially intensifying the molecular breeding programs of Coffea spp. plants.

A Gene Regulatory Network Controlled by BpERF2 and BpMYB102 in Birch under Drought Conditions

Gene expression profiles are powerful tools for investigating mechanisms of plant stress tolerance. Betula platyphylla (birch) is a widely distributed tree, but its drought-tolerance mechanism has been little studied. Using RNA-Seq, we identified 2917 birch genes involved in its response to drought stress. These drought-responsive genes include the late embryogenesis abundant (LEA) family, heat shock protein (HSP) family, water shortage-related and ROS-scavenging proteins, and many transcription factors (TFs). Among the drought-induced TFs, the ethylene responsive factor (ERF) and myeloblastosis oncogene (MYB) families were the most abundant. BpERF2 and BpMYB102, which were strongly induced by drought and had high transcription levels, were selected to study their regulatory networks. BpERF2 and BpMYB102 both played roles in enhancing drought tolerance in birch. Chromatin immunoprecipitation combined with qRT-PCR indicated that BpERF2 regulated genes such as those in the LEA and HSP families, while BpMYB102 regulated genes such as Pathogenesis-related Protein 1 (PRP1) and 4-Coumarate:Coenzyme A Ligase 10 (4CL10). Multiple genes were regulated by both BpERF2 and BpMYB102. We further characterized the function of some of these genes, and the genes that encode Root Primordium Defective 1 (RPD1), PRP1, 4CL10, LEA1, SOD5, and HSPs were found to be involved in drought tolerance. Therefore, our results suggest that BpERF2 and BpMYB102 serve as transcription factors that regulate a series of drought-tolerance genes in B. platyphylla to improve drought tolerance.

Genome-Wide Association Studies in Apple Reveal Loci for Aroma Volatiles, Sugar Composition, and Harvest Date

Understanding the genetic architecture of fruit quality traits is crucial to target breeding of apple ( L.) cultivars. We linked genotype and phenotype information by combining genotyping-by-sequencing (GBS) generated single nucleotide polymorphism (SNP) markers with fruit flavor volatile data, sugar and acid content, and historical trait data from a gene bank collection. Using gas chromatography-mass spectrometry (GC-MS) analysis of apple juice samples, we identified 49 fruit volatile organic compounds (VOCs). We found a very variable content of VOCs, especially for the esters, among 149 apple cultivars. We identified convincing associations for the acetate esters especially butyl acetate and hexyl acetate on chromosome 2 in a region of several alcohol acyl-transferases including AAT1. For sucrose content and for fructose and sucrose in percentage of total sugars, we revealed significant SNP associations. Here, we suggest a vacuolar invertase close to significant SNPs for this association as candidate gene. Harvest date was in strong SNP association with a NAC transcription factor gene and sequencing identified two haplotypes associated with harvest date. The study shows that SNP marker characterization of a gene bank collection can be successfully combined with new and historical trait data for association studies. Suggested candidate genes may contribute to an improved understanding of the genetic basis for important traits and simultaneously provide tools for targeted breeding using marker-assisted selection (MAS).

Molecular Events Occurring During Softening of Strawberry Fruit

Changes in fruit texture taking place during ripening, described as softening, are mainly due to alterations in structure and/or composition of the cell wall. Several non-covalent interactions between the three carbohydrate polymers of the cell wall, cellulose, pectins and hemicellulose, and many structural proteins and ions, enable a complex structure. During softening, the disassembly of the cell wall structure takes place, mediated by a complete set of cell wall degrading enzymes or proteins. Softening is a coordinated event that requires the orchestrated participation of a wide variety of proteins. Plant hormones and a set of transcription factors are the organizers of this multi-protein effort. Strawberry is a non climacteric fruit that softens intensively during the last stages of development. The Chilean strawberry fruit (Fragaria chiloensis), the maternal relative of the commercial strawberry (F. × ananassa), softens even faster than commercial strawberry. Softening of the Chilean strawberry fruit has been studied at different levels: changes in cell wall polymers, activity of cell wall degrading enzymes and transcriptional changes of their genes, providing a general view of the complex process. The search for the 'orchestra director' that could coordinate softening events in strawberry fruit has been focussed on hormones like ABA and auxins, and more precisely the relation ABA/AUX. These hormones regulate the expression of many cell wall degrading enzyme genes, and this massive transcriptional change that takes place involves the participation of key transcriptional factors (TF). This review provides an update of the present knowledge regarding the softening of strawberry fruit. Nevertheless, the entire softening process is still under active research especially for the great influence of texture on fruit quality and its high impact on fruit shelf life, and therefore it is expected that new and promising information will illuminate the field in the near future.

Tomato fruit ripening factor NOR controls leaf senescence

NAC transcription factors (TFs) are important regulators of expressional reprogramming during plant development, stress responses, and leaf senescence. NAC TFs also play important roles in fruit ripening. In tomato (Solanum lycopersicum), one of the best characterized NACs involved in fruit ripening is NON-RIPENING (NOR), and the non-ripening (nor) mutation has been widely used to extend fruit shelf life in elite varieties. Here, we show that NOR additionally controls leaf senescence. Expression of NOR increases with leaf age, and developmental as well as dark-induced senescence are delayed in the nor mutant, while overexpression of NOR promotes leaf senescence. Genes associated with chlorophyll degradation as well as senescence-associated genes (SAGs) show reduced and elevated expression, respectively, in nor mutants and NOR overexpressors. Overexpression of NOR also stimulates leaf senescence in Arabidopsis thaliana. In tomato, NOR supports senescence by directly and positively regulating the expression of several senescence-associated genes including, besides others, SlSAG15 and SlSAG113, SlSGR1, and SlYLS4. Finally, we find that another senescence control NAC TF, namely SlNAP2, acts upstream of NOR to regulate its expression. Our data support a model whereby NAC TFs have often been recruited by higher plants for both the control of leaf senescence and fruit ripening.

Genome-wide analysis, expansion and expression of the NAC family under drought and heat stresses in bread wheat (T. aestivum L.)

The NAC family is one of the largest plant-specific transcription factor families, and some of its members are known to play major roles in plant development and response to biotic and abiotic stresses. Here, we inventoried 488 NAC members in bread wheat (Triticum aestivum). Using the recent release of the wheat genome (IWGS RefSeq v1.0), we studied duplication events focusing on genomic regions from 4B-4D-5A chromosomes as an example of the family expansion and neofunctionalization of TaNAC members. Differentially expressed TaNAC genes in organs and in response to abiotic stresses were identified using publicly available RNAseq data. Expression profiling of 23 selected candidate TaNAC genes was studied in leaf and grain from two bread wheat genotypes at two developmental stages in field drought conditions and revealed insights into their specific and/or overlapping expression patterns. This study showed that, of the 23 TaNAC genes, seven have a leaf-specific expression and five have a grain-specific expression. In addition, the grain-specific genes profiles in response to drought depend on the genotype. These genes may be considered as potential candidates for further functional validation and could present an interest for crop improvement programs in response to climate change. Globally, the present study provides new insights into evolution, divergence and functional analysis of NAC gene family in bread wheat.

Abscisic Acid Regulates Anthocyanin Biosynthesis and Gene Expression Associated With Cell Wall Modification in Ripening Bilberry (Vaccinium myrtillus L.) Fruits

Ripening of non-climacteric bilberry (Vaccinium myrtillus L.) fruit is characterized by a high accumulation of health-beneficial anthocyanins. Plant hormone abscisic acid (ABA) and sucrose have been shown to be among the central signaling molecules coordinating non-climacteric fruit ripening and anthocyanin accumulation in some fruits such as strawberry. Our earlier studies have demonstrated an elevation in endogenous ABA level in bilberry fruit at the onset of ripening indicating a role for ABA in the regulation of bilberry fruit ripening. In the present study, we show that the treatment of unripe green bilberry fruits with exogenous ABA significantly promotes anthocyanin biosynthesis and accumulation both in fruits attached and detached to the plant. In addition, ABA biosynthesis inhibitor, fluridone, delayed anthocyanin accumulation in bilberries. Exogenous ABA also induced the expression of several genes involved in cell wall modification in ripening bilberry fruits. Furthermore, silencing of VmNCED1, the key gene in ABA biosynthesis, was accompanied by the down-regulation in the expression of key anthocyanin biosynthetic genes. In contrast, the treatment of unripe green bilberry fruits with exogenous sucrose or glucose did not lead to an enhancement in the anthocyanin accumulation neither in fruits attached to plant nor in post-harvest fruits. Moreover, sugars failed to induce the expression of genes associated in anthocyanin biosynthesis or ABA biosynthesis while could elevate expression of some genes associated with cell wall modification in post-harvest bilberry fruits. Our results demonstrate that ABA plays a major role in the regulation of ripening-related processes such as anthocyanin biosynthesis and cell wall modification in bilberry fruit, whereas sugars seem to have minor regulatory roles in the processes. The results indicate that the regulation of bilberry fruit ripening differs from strawberry that is currently considered as a model of non-climacteric fruit ripening. In this study, we also identified transcription factors, which expression was enhanced by ABA, as potential regulators of ABA-mediated bilberry fruit ripening processes.