A homolog of NO APICAL MERISTEM is an immediate target of the floral homeotic genes APETALA3/PISTILLATA

ArNAC148 induces Acer rubrum leaf senescence by activating the transcription of the ABA receptor gene ArPYR13

Acer rubrum, an ornamental tree known for its stunning autumn colors, has an elusive molecular mechanism that governs its leaf senescence. We performed the genome-wide analysis of NAC transcription factor genes and PYRABACTIN RESISTANCE1-LIKE (PYLs) and found that ArNAC148 and ArPYL13 were significantly upregulated in senescing leaves as compared to mature leaves. Subcellular localization studies confirmed the nuclear localization of ArNAC148 and the cytoplasmic localization of ArPYL13. Electrophoretic mobility shift assay and yeast one-hybrid assay demonstrated that ArNAC148 directly binds to the promoter of ArPYL13. Luciferase reporter assays further showed that ArNAC148 activates the transcription of ArPYL13. The transient expression of ArNAC148 and ArPYL13 in tobacco leaves promoted chlorophyll degradation, increased H2O2 level, MDA contents, and electrolyte leakage in response to abscisic acid (ABA). Moreover, the virus-induced gene silencing of ArNAC148 and ArPYL13 in A. rubrum produced results that were opposite to those observed in transient expression experiments. Our findings suggest that ArNAC148 induces leaf senescence by directly activating the transcription of ArPYL13, providing insights into the ABA-mediated regulatory mechanisms governing leaf senescence in A. rubrum. This study offers new perspectives for researchers to explore the roles of NAC and PYL genes in regulating leaf senescence in woody ornamental plants.

Genome-wide investigation and analysis of NAC transcription factor family in Populus tomentosa and expression analysis under salt stress

The NAC transcription factor family is one of the largest families of TFs in plants, and members of NAC gene family play important roles in plant growth and stress response. Recent release of the haplotype-resolved genome assembly of P. tomentosa provide a platform for NAC protein genome-wide analysis. A total of 270 NAC genes were identified and a comprehensive overview of the PtoNAC gene family is presented, including gene promoter, structure and conserved motif analyses, chromosome localization and collinearity analysis, protein phylogeny, expression pattern, and interaction analysis. The results indicate that protein length, molecular weight, and theoretical isoelectric points of the NAC TF family vary, while gene structure and motif are relatively conserved. Chromosome mapping analysis showed that the P. tomentosa NAC genes are unevenly distributed on 19 chromosomes. The interchromosomal evolutionary results indicate 12 pairs of tandem and 280 segmental duplications. Segmental duplication is possibly related to amplification of P. tomentosa NAC gene family. Expression patterns of 35 PtoNAC genes from P. tomentosa subgroup were analysed under high salinity, and seven NAC genes were induced by this treatment. Promoter and protein interaction network analyses showed that PtoNAC genes are closely associated with growth, development, and abiotic and biotic stress, especially salt stress. These results provide a meaningful reference for follow-up studies of the functional characteristics of NAC genes in the mechanism of stress response and their potential roles in development of P. tomentosa.

Functional role of geminivirus encoded proteins in the host: Past and present

During plant-pathogen interaction, plant exhibits a strong defense system utilizing diverse groups of proteins to suppress the infection and subsequent establishment of the pathogen. However, in response, pathogens trigger an anti-silencing mechanism to overcome the host defense machinery. Among plant viruses, geminiviruses are the second largest virus family with a worldwide distribution and continue to be production constraints to food, feed, and fiber crops. These viruses are spread by a diverse group of insects, predominantly by whiteflies, and are characterized by a single-stranded DNA (ssDNA) genome coding for four to eight proteins that facilitate viral infection. The most effective means to managing these viruses is through an integrated disease management strategy that includes virus-resistant cultivars, vector management, and cultural practices. Dynamic changes in this virus family enable the species to manipulate their genome organization to respond to external changes in the environment. Therefore, the evolutionary nature of geminiviruses leads to new and novel approaches for developing virus-resistant cultivars and it is essential to study molecular ecology and evolution of geminiviruses. This review summarizes the multifunctionality of each geminivirus-encoded protein. These protein-based interactions trigger the abrupt changes in the host methyl cycle and signaling pathways that turn over protein normal production and impair the plant antiviral defense system. Studying these geminivirus interactions localized at cytoplasm-nucleus could reveal a more clear picture of host-pathogen relation. Data collected from this antagonistic relationship among geminivirus, vector, and its host, will provide extensive knowledge on their virulence mode and diversity with climate change.

Characteristics of NAC transcription factors in Solanaceae crops and their roles in responding to abiotic and biotic stresses

As one of the largest transcription factor (TF) families in plants, the NAC (NAM, ATAF1/2, and CUC2) family plays important roles in response pathways to various abiotic and biotic stresses, such as drought, high salinity, low temperature, and pathogen infection. Although, there are a number of reviews on the involvement of NAC TF in plant responses to biotic and abiotic stresses, most of them are focused on the model plants Arabidopsis thaliana and Oryza sativa, and there is a lack of systematic evaluation of specific species. Solanaceae, the world's third most significant cash crop, has been seriously affected by environmental disturbances in recent years in terms of yield and quality, posing a severe threat to global food security. This review focuses on the functional roles of NAC transcription factors in response to external stresses involved in five important Solanaceae crops: tomato, potato, pepper, eggplant and tobacco, and analyzes the affinities between them. It will provide resources for stress-resistant breeding of Solanaceae crops using transgenic technology.

Transcriptional Control of Seed Life: New Insights into the Role of the NAC Family

Transcription factors (TFs) regulate gene expression by binding to specific sequences on DNA through their DNA-binding domain (DBD), a universal process. This update conveys information about the diverse roles of TFs, focusing on the NACs (NAM-ATAF-CUC), in regulating target-gene expression and influencing various aspects of plant biology. NAC TFs appeared before the emergence of land plants. The NAC family constitutes a diverse group of plant-specific TFs found in mosses, conifers, monocots, and eudicots. This update discusses the evolutionary origins of plant NAC genes/proteins from green algae to their crucial roles in plant development and stress response across various plant species. From mosses and lycophytes to various angiosperms, the number of NAC proteins increases significantly, suggesting a gradual evolution from basal streptophytic green algae. NAC TFs play a critical role in enhancing abiotic stress tolerance, with their function conserved in angiosperms. Furthermore, the modular organization of NACs, their dimeric function, and their localization within cellular compartments contribute to their functional versatility and complexity. While most NAC TFs are nuclear-localized and active, a subset is found in other cellular compartments, indicating inactive forms until specific cues trigger their translocation to the nucleus. Additionally, it highlights their involvement in endoplasmic reticulum (ER) stress-induced programmed cell death (PCD) by activating the vacuolar processing enzyme (VPE) gene. Moreover, this update provides a comprehensive overview of the diverse roles of NAC TFs in plants, including their participation in ER stress responses, leaf senescence (LS), and growth and development. Notably, NACs exhibit correlations with various phytohormones (i.e., ABA, GAs, CK, IAA, JA, and SA), and several NAC genes are inducible by them, influencing a broad spectrum of biological processes. The study of the spatiotemporal expression patterns provides insights into when and where specific NAC genes are active, shedding light on their metabolic contributions. Likewise, this review emphasizes the significance of NAC TFs in transcriptional modules, seed reserve accumulation, and regulation of seed dormancy and germination. Overall, it effectively communicates the intricate and essential functions of NAC TFs in plant biology. Finally, from an evolutionary standpoint, a phylogenetic analysis suggests that it is highly probable that the WRKY family is evolutionarily older than the NAC family.

Isolation, Characterization, and Expression Analysis of NAC Transcription Factor from Andrographis paniculata (Burm. f.) Nees and Their Role in Andrographolide Production

Andrographis paniculata (Burm. f.) Nees is an important medicinal plant known for its bioactive compound andrographolide. NAC transcription factors (NAM, ATAF1/2, and CUC2) play a crucial role in secondary metabolite production, stress responses, and plant development through hormonal signaling. In this study, a putative partial transcript of three NAC family genes (ApNAC83, ApNAC21 22 and ApNAC02) was used to isolate full length genes using RACE. Bioinformatics analyses such as protein structure prediction, cis-acting regulatory elements, and gene ontology analysis were performed. Based on in silico predictions, the diterpenoid profiling of the plant's leaves (five-week-old) and the real-time PCR-based expression analysis of isolated NAC genes under abscisic acid (ABA) treatment were performed. Additionally, the expression analysis of isolated NAC genes under MeJA treatment and transient expression in Nicotiana tabacum was performed. Full-length sequences of three members of the NAC transcription factor family, ApNAC83 (1102 bp), ApNAC21 22 (996 bp), and ApNAC02 (1011 bp), were isolated and subjected to the promoter and gene ontology analysis, which indicated their role in transcriptional regulation, DNA binding, ABA-activated signaling, and stress management. It was observed that ABA treatment leads to a higher accumulation of andrographolide and 14-deoxyandrographolide content, along with the upregulation of ApNAC02 (9.6-fold) and the downregulation of ApNAC83 and ApNAC21 22 in the leaves. With methyl jasmonate treatment, ApNAC21 22 expression decreased, while ApNAC02 increased (1.9-fold), with no significant change being observed in ApNAC83. The transient expression of the isolated NAC genes in a heterologous system (Nicotiana benthamiana) demonstrated their functional transcriptional activity, leading to the upregulation of the NtHMGR gene, which is related to the terpene pathway in tobacco. The expression analysis and heterologous expression of ApNAC21 22 and ApNAC02 indicated their role in andrographolide biosynthesis.

NACs strike again: NOR-like1 is responsible for cuticle development in tomato fruit

This article comments on:

Liu G-S, Huang H, Grierson D, Gao Y, Ji X, Peng Z-Z, Li H-L, Niu X-L, Jia W, He J-L, Xiang L-T, Gao H-Y, Qu G-Q, Zhu H-L, Zhu B-Z, Luo Y-B, Fu D-Q. 2024. NAC transcription factor SlNOR-like1 plays a dual regulatory role in tomato fruit cuticle formation. Journal of Experimental Botany 75, 1903–1918.

Transcriptional regulation of tomato fruit ripening

An intrinsic and genetically determined ripening program of tomato fruits often depends upon the appropriate activation of tissue- and stage-specific transcription factors in space and time. The past two decades have yielded considerable progress in detailing these complex transcriptional as well as hormonal regulatory circuits paramount to fleshy fruit ripening. This non-linear ripening process is strongly controlled by the MADS-box and NOR family of proteins, triggering a transcriptional response associated with the progression of fruit ripening. Deepening insights into the connection between MADS-RIN and plant hormones related transcription factors, such as ERFs and ARFs, further conjugates the idea that several signaling units work in parallel to define an output fruit ripening transcriptome. Besides these TFs, the role of other families of transcription factors such as MYB, GLK, WRKY, GRAS and bHLH have also emerged as important ripening regulators. Other regulators such as EIN and EIL proteins also determine the transcriptional landscape of ripening fruits. Despite the abundant knowledge of the complex spectrum of ripening networks in the scientific domain, identifying more ripening effectors would pave the way for a better understanding of fleshy fruit ripening at the molecular level. This review provides an update on the transcriptional regulators of tomato fruit ripening.

Genome-wide identification and characterization of greenbug-inducible NAC transcription factors in sorghum

BACKGROUND

Sorghum (Sorghum bicolor) is an important cereal crop grown worldwide because of its multipurpose uses such as food, forage, and bioenergy feedstock and its wide range of adaption even in marginal environments. Greenbug can cause severe damage to sorghum plants and yield loss. Plant NAC transcription factors (TFs) have been reported to have diverse functions in plant development and plant defense but has not been studied in sorghum yet.

METHODS AND RESULTS

In this study, a comprehensive analysis of the sorghum NAC (SbNAC) gene family was conducted through genome-wide analysis. A total of 112 NAC genes has been identified in the sorghum genome. These SbNAC genes are phylogenetically clustered into 15 distinct subfamilies and unevenly distribute in clusters at the telomeric ends of each chromosome. Twelve pairs of SbNAC genes are possibly involved in the segmental duplication among nine chromosomes except chromosome 10. Structure analysis showed the diverse structures with a highly variable number of exons in the SbNAC genes. Furthermore, most of the SbNAC genes showed specific temporal and spatial expression patterns according to the results of RNA-seq analysis, suggesting their diverse functions during sorghum growth and development. We have also identified nine greenbug-inducible SbNAC genes by comparing the expression profiles between two sorghum genotypes (susceptible BTx623 and resistant PI607900) in response to greenbug infestation.

CONCLUSIONS

Our systematic analysis of the NAC gene expression profiles provides both a preliminary survey into their roles in plant defense against insect pests and a useful reference for in-depth characterization of the SbNAC genes and the regulatory network that contributes genetic resistance to aphids.

An insertion of transposon in DcNAP inverted its function in the ethylene pathway to delay petal senescence in carnation (Dianthus caryophyllus L.)

Petal senescence is the final stage of flower development. Transcriptional regulation plays key roles in this process. However, whether and how post-transcriptional regulation involved is still largely unknown. Here, we identified an ethylene-induced NAC family transcription factor DcNAP in carnation (Dianthus caryophyllus L.). One allele, DcNAP-dTdic1, has an insertion of a dTdic1 transposon in its second exon. The dTdic1 transposon disrupts the structure of DcNAP and causes alternative splicing, which transcribes multiple domain-deleted variants (DcNAP2 and others). Conversely, the wild type allele DcNAP transcribes DcNAP1 encoding an intact NAC domain. Silencing DcNAP1 delays and overexpressing DcNAP1 accelerates petal senescence in carnation, while silencing and overexpressing DcNAP2 have the opposite effects, respectively. Further, DcNAP2 could interact with DcNAP1 and interfere the binding and activation activity of DcNAP1 to the promoters of its downstream target ethylene biosynthesis genes DcACS1 and DcACO1. Lastly, ethylene signalling core transcriptional factor DcEIL3-1 can activate the expression of DcNAP1 and DcNAP2 in the same way by binding their promoters. In summary, we discovered a novel mechanism by which DcNAP regulates carnation petal senescence at the post-transcriptional level. It may also provide a useful strategy to manipulate the NAC domains of NAC transcription factors for crop genetic improvement.

Genome-Wide Identification and Characterization of the NAC Gene Family and Its Involvement in Cold Response in Dendrobium officinale

The NAC (NAM, ATAF1/2 and CUC2) gene family is one of the largest plant-specific transcription factor families, functioning as crucial regulators in diverse biological processes such as plant growth and development as well as biotic and abiotic stress responses. Although it has been widely characterized in many plants, the significance of the NAC family in Dendrobium officinale remained elusive up to now. In this study, a genome-wide search method was conducted to identify NAC genes in Dendrobium officinale (DoNACs) and a total of 110 putative DoNACs were obtained. Phylogenetic analysis classified them into 15 subfamilies according to the nomenclature in Arabidopsis and rice. The members in the subfamilies shared more similar gene structures and conversed protein domain compositions. Furthermore, the expression profiles of these DoNACs were investigated in diverse tissues and under cold stress by RNA-seq data. Then, a total of five up-regulated and five down-regulated, cold-responsive DoNACs were validated through QRT-PCR analysis, demonstrating they were involved in regulating cold stress response. Additionally, the subcellular localization of two down-regulated candidates (DoNAC39 and DoNAC58) was demonstrated to be localized in the nuclei. This study reported the genomic organization, protein domain compositions and expression patterns of the NAC family in Dendrobium officinale, which provided targets for further functional studies of DoNACs and also contributed to the dissection of the role of NAC in regulating cold tolerance in Dendrobium officinale.

The Abundant and Unique Transcripts and Alternative Splicing of the Artificially Autododecaploid London Plane (Platanus × acerifolia)

Transcription and alternative splicing (AS) are now appreciated in plants, but few studies have examined the effects of changing ploidy on transcription and AS. In this study, we showed that artificially autododecaploid plants of London plane (Platanus × acerifolia (Aiton) Willd) had few flowers relative to their hexaploid progenitors. Transcriptome analysis based on full-length Oxford Nanopore Technologies (ONTs) and next-generation sequencing (NGS) revealed that the increased ploidy level in P. × acerifolia led to more transcribed isoforms, accompanied by an increase in the number of isoforms per gene. The functional enrichment of genes indicated that novel genes transcribed specifically in the dodecaploids may have been highly correlated with the ability to maintain genome stability. The dodecaploids showed a higher number of genes with upregulated differentially expressed genes (DEGs) compared with the hexaploid counterpart. The genome duplication of P. × acerifolia resulted mainly in the DEGs involved in basic biological pathways. It was noted that there was a greater abundance of alternative splicing (AS) events and AS genes in the dodecaploids compared with the hexaploids in P. × acerifolia. In addition, a significant difference between the structure and expression of AS events between the hexaploids and dodecaploids of Platanus was found. Of note, some DEGs and differentially spliced genes (DSGs) related to floral transition and flower development were consistent with the few flower traits in the dodecaploids of P. × acerifolia. Collectively, our findings explored the difference in transcription and AS regulation between the hexaploids and dodecaploids of P. × acerifolia and gained new insight into the molecular mechanisms underlying the few-flower phenotype of P. × acerifolia. These results contribute to uncovering the regulatory role of transcription and AS in polyploids and breeding few-flower germplasms.

A NAC transcription factor ZaNAC93 confers floral initiation, fruit development, and prickle formation in Zanthoxylum armatum

Zanthoxylum armatum is a dioecious prickly plant which developed apomictic reproduction. The increases in male flowers and prickle density in female plants lead to low yield and picking efficiency. However, little is known concerning the mechanisms of floral development and prickle formation. NAC is a well-known transcription factor that participates in multiple aspects of plant growth and development. Herein, we characterize the functions and regulatory mechanisms of candidate NACs controlling both traits in Z. armatum. A total of 159 ZaNACs were identified, and 16 of these were male-biased, represented by the NAP subfamily members ZaNAC93 and ZaNAC34, orthologs of AtNAC025 and AtNARS1/NAC2 respectively. Overexpression of ZaNAC93 in tomato led to modifications in flower and fruit development, including earlier flowering, increased numbers of lateral shoots and flowers, accelerated plant senescence, and reduced size and weight of fruits and seeds. In addition, the trichome density in leaves and inflorescences was dramatically reduced in ZaNAC93-OX lines. Overexpression of ZaNAC93 resulted in the up-/downregulation of genes associated with GA, ABA and JA signaling pathways, such as GAI, PYL and JAZ, as well as several TFs, including bZIP2, AGL11, FBP24 and MYB52. Yeast two-hybrid analysis revealed that ZaNAC93 protein could interact with AP1, GAI, bZIP2 and AGL11 in Z. armatum, which might contribute to floral induction, fruit growth, and trichome initiation. This work provides new insights into the molecular mechanisms of ZaNAC93 in reproductive development and prickle formation in Z. armatum.

The NAC transcription factor ZmNAC132 regulates leaf senescence and male fertility in maize

Leaf senescence is an integral step in the final stages of plant development, as nutrient remobilization from leaves to sink organs is accomplished during this process. NACs compose a large superfamily of plant-specific TFs involved in multiple plant development processes. Here, we identified a maize NAC TF, ZmNAC132, involved in leaf senescence and male fertility. ZmNAC132 expression was tightly linked to leaf senescence in an age-dependent manner. Knockout of ZmNAC132 led to delays in chlorophyll degradation and leaf senescence, whereas overexpression of ZmNAC132 had the opposite effects. ZmNAC132 could bind to and transactivate the promoter of ZmNYE1, a major chlorophyll catabolic gene, to accelerate chlorophyll degradation during leaf senescence. Moreover, ZmNAC132 affected male fertility through the upregulation of ZmEXPB1, an expansin-encoding gene associated with sexual reproduction and other related genes. Together, the results show that ZmNAC132 participates in the regulation of leaf senescence and male fertility through the targeting of different downstream genes in maize.

The ABA-induced NAC transcription factor MdNAC1 interacts with a bZIP-type transcription factor to promote anthocyanin synthesis in red-fleshed apples

Anthocyanins are valuable compounds in red-fleshed apples. The MdMYB10 transcription factor is an important regulator of the anthocyanin synthesis pathway. However, other transcription factors are key components of the complex network controlling anthocyanin synthesis and should be more thoroughly characterized. In this study, we used a yeast-based screening technology to identify MdNAC1 as a transcription factor that positively regulates anthocyanin synthesis. The overexpression of MdNAC1 in apple fruits and calli significantly promoted the accumulation of anthocyanins. In binding experiments, we demonstrated that MdNAC1 combines with the bZIP-type transcription factor MdbZIP23 to activate the transcription of MdMYB10 and MdUFGT. Our analyses also indicated that the expression of MdNAC1 is strongly induced by ABA because of the presence of an ABRE cis-acting element in its promoter. Additionally, the accumulation of anthocyanins in apple calli co-transformed with MdNAC1 and MdbZIP23 increased in the presence of ABA. Therefore, we revealed a novel anthocyanin synthesis mechanism involving the ABA-induced transcription factor MdNAC1 in red-fleshed apples.

Comparative functional analysis of PdeNAC2 and AtVND6 in the tracheary element formation

Tracheary elements (i.e., vessel elements and tracheids) are highly specialized, non-living cells present in the water-conducting xylem tissue. In angiosperms, proteins in the VASCULAR-RELATED NAC-DOMAIN (VND) subgroup of the NAC transcription factor family (e.g., AtVND6) are required for the differentiation of vessel elements through transcriptional regulation of genes responsible for secondary cell wall (SCW) formation and programmed cell death (PCD). Gymnosperms, however, produce only tracheids, the mechanism of which remains elusive. Here, we report functional characteristics of PdeNAC2, a VND homolog in Pinus densiflora, as a key regulator of tracheid formation. Interestingly, our molecular genetic analyses show that PdeNAC2 can induce the formation of vessel element-like cells in angiosperm plants, demonstrated by transgenic overexpression of either native or NAC domain-swapped synthetic genes of PdeNAC2 and AtVND6 in both Arabidopsis and hybrid poplar. Subsequently, genome-wide identification of direct target genes of PdeNAC2 and AtVND6 revealed 138 and 174 genes as putative direct targets, respectively, but only 17 genes were identified as common direct targets. Further analyses have found that PdeNAC2 does not control some AtVND6-dependent vessel differentiation genes in angiosperm plants, such as AtVRLK1, LBD15/30, and pit-forming ROP signaling genes. Collectively, our results suggest that different target gene repertoires of PdeNAC2 and AtVND6 may contribute to the evolution of tracheary elements.

The NAC transcription factor family in Eucommia ulmoides: Genome-wide identification, characterization, and network analysis in relation to the rubber biosynthetic genes

The NAC transcription factor family is a large plant gene family, participating in plant growth and development, secondary metabolite synthesis, biotic and abiotic stresses responses, and hormone signaling. Eucommia ulmoides is a widely planted economic tree species in China that can produce trans-polyisoprene: Eucommia rubber (Eu-rubber). However, genome-wide identification of the NAC gene family has not been reported in E. ulmoides. In this study, 71 NAC proteins were identified based on genomic database of E. ulmoides. Phylogenetic analysis showed that the EuNAC proteins were distributed in 17 subgroups based on homology with NAC proteins in Arabidopsis, including the E. ulmoides-specific subgroup Eu_NAC. Gene structure analysis suggested that the number of exons varied from 1 to 7, and multitudinous EuNAC genes contained two or three exons. Chromosomal location analysis revealed that the EuNAC genes were unevenly distributed on 16 chromosomes. Three pairs of genes of tandem duplicates genes and 12 segmental duplications were detected, which indicated that segmental duplications may provide the primary driving force of expansion of EuNAC. Prediction of cis-regulatory elements indicated that the EuNAC genes were involved in development, light response, stress response and hormone response. For the gene expression analysis, the expression levels of EuNAC genes in various tissues were quite different. To explore the effect of EuNAC genes on Eu-rubber biosynthesis, a co-expression regulatory network between Eu-rubber biosynthesis genes and EuNAC genes was constructed, which indicated that six EuNAC genes may play an important role in the regulation of Eu-rubber biosynthesis. In addition, this six EuNAC genes expression profiles in E. ulmoides different tissues were consistent with the trend in Eu-rubber content. Quantitative real-time PCR analysis showed that EuNAC genes were responsive to different hormone treatment. These results will provide a useful reference for further studies addressing the functional characteristics of the NAC genes and its potential role in Eu-rubber biosynthesis.

Open questions in plant cell wall synthesis

Plant cells are surrounded by strong yet flexible polysaccharide-based cell walls that support the cell while also allowing growth by cell expansion. Plant cell wall research has advanced tremendously in recent years. Sequenced genomes of many model and crop plants have facilitated cataloging and characterization of many enzymes involved in cell wall synthesis. Structural information has been generated for several important cell wall synthesizing enzymes. Important tools have been developed including antibodies raised against a variety of cell wall polysaccharides and glycoproteins, collections of enzyme clones and synthetic glycan arrays for characterizing enzymes, herbicides that specifically affect cell wall synthesis, live-cell imaging probes to track cell wall synthesis, and an inducible secondary cell wall synthesis system. Despite these advances, and often because of the new information they provide, many open questions about plant cell wall polysaccharide synthesis persist. This article highlights some of the key questions that remain open, reviews the data supporting different hypotheses that address these questions, and discusses technological developments that may answer these questions in the future.

Genome-wide identification, evolution and expression analysis of NAC gene family under salt stress in wild emmer wheat (Triticum dicoccoides. L)

The NAC transcription factor (TF) family is one of the largest plant-specific gene families, playing the vital roles in plant growth and development as well as stress response. Although it has been extensively characterized in many plants, the significance of NAC family in wild emmer wheat is not well understood up to now. Here, a total of 200 NAC transcription factors were identified in wild emmer (TdNACs) through a genome-search method, which were classified into 12 subfamilies based on phylogenetic relationship. And the members in the subfamily shared similar exon-intron structure and conversed domain organization. Collinearity analysis revealed that segmental duplication and polyploidization contributed mainly to the expansion of TdNACs. Furthermore, the genetic variations of TdNACs were investigated using the re-sequencing data and genetic bottleneck has occurred on NAC genes when wild emmer domesticated to cultivated emmer wheat. Finally, the expression patterns of these TdNACs were investigated using RNA-seq data of the salt-tolerant genotype under salt stress to obtain salt-responsive TdNACs, and 10 out of which were further validated using QPCR analysis. This study provided the targets for further functional study of TdNAC genes, and also contributed to mine novel genes for improving the salt tolerance in wheat and other crops.

Orchid NAC Transcription Factors: A Focused Analysis of CUPULIFORMIS Genes

Plant transcription factors are involved in different developmental pathways. NAC transcription factors (No Apical Meristem, Arabidopsis thaliana Activating Factor, Cup-shaped Cotyledon) act in various processes, e.g., plant organ formation, response to stress, and defense mechanisms. In Antirrhinum majus, the NAC transcription factor CUPULIFORMIS (CUP) plays a role in determining organ boundaries and lip formation, and the CUP homologs of Arabidopsis and Petunia are involved in flower organ formation. Orchidaceae is one of the most species-rich families of angiosperms, known for its extraordinary diversification of flower morphology. We conducted a transcriptome and genome-wide analysis of orchid NACs, focusing on the No Apical Meristem (NAM) subfamily and CUP genes. To check whether the CUP homologs could be involved in the perianth formation of orchids, we performed an expression analysis on the flower organs of the orchid Phalaenopsis aphrodite at different developmental stages. The expression patterns of the CUP genes of P. aphrodite suggest their possible role in flower development and symmetry establishment. In addition, as observed in other species, the orchid CUP1 and CUP2 genes seem to be regulated by the microRNA, miR164. Our results represent a preliminary study of NAC transcription factors in orchids to understand the role of these genes during orchid flower formation.

Transcriptome Profiling of Stem-Differentiating Xylem in Response to Abiotic Stresses Based on Hybrid Sequencing in Cunninghamia lanceolata

Cunninghamia lanceolata (C. lanceolata) belongs to Gymnospermae, which are fast-growing and have desirable wood properties. However, C. lanceolata's stress resistance is little understood. To unravel the physiological and molecular regulation mechanisms under environmental stresses in the typical gymnosperm species of C. lanceolata, three-year-old plants were exposed to simulated drought stress (polyethylene glycol 8000), salicylic acid, and cold treatment at 4 °C for 8 h, 32 h, and 56 h, respectively. Regarding the physiological traits, we observed a decreased protein content and increased peroxidase upon salicylic acid and polyethylene glycol treatment. Superoxide dismutase activity either decreased or increased at first and then returned to normal under the stresses. Regarding the molecular regulation, we used both nanopore direct RNA sequencing and short-read sequencing to reveal a total of 5646 differentially expressed genes in response to different stresses, of which most had functions in lignin catabolism, pectin catabolism, and xylan metabolism, indicating that the development of stem-differentiating xylem was affected upon stress treatment. Finally, we identified a total of 51 AP2/ERF, 29 NAC, and 37 WRKY transcript factors in C. lanceolata. The expression of most of the NAC TFs increased under cold stress, and the expression of most of the WRKY TFs increased under cold and SA stress. These results revealed the transcriptomics responses in C. lanceolata to short-term stresses under this study's experimental conditions and provide preliminary clues about stem-differentiating xylem changes associated with different stresses.

FvNST1b NAC Protein Induces Secondary Cell Wall Formation in Strawberry

Secondary cell wall thickening plays a crucial role in plant growth and development. Diploid woodland strawberry (Fragaria vesca) is an excellent model for studying fruit development, but its molecular control of secondary wall thickening is largely unknown. Previous studies have shown that Arabidopsis NAC secondary wall thickening promoting factor1 (AtNST1) and related proteins are master regulators of xylem fiber cell differentiation in multiple plant species. In this study, a NST1-like gene, FvNST1b, was isolated and characterized from strawberry. Sequence alignment and phylogenetic analysis showed that the FvNST1b protein contains a highly conserved NAC domain, and it belongs to the same family as AtNST1. Overexpression of FvNST1b in wild-type Arabidopsis caused extreme dwarfism, induced ectopic thickening of secondary walls in various tissues, and upregulated the expression of genes related to secondary cell wall synthesis. In addition, transient overexpression of FvNST1b in wild-type Fragaria vesca fruit produced cells resembling tracheary elements. These results suggest that FvNST1b positively regulates secondary cell wall formation as orthologous genes from other species.

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.

Rapeseed NAM transcription factor positively regulates leaf senescence via controlling senescence-associated gene expression

Leaf senescence is one of the most visible forms of programmed cell death in plants. It can be a seasonal adaptation in trees or the final stage in crops ensuring efficient translocation of nutrients to seeds. Along with developmental cues, various environmental factors could also trigger the onset of senescence through transcriptional cascades. Rapeseed (Brassica napus L.) is an important oil crop with its yielding affected by significant falling leaves as a result of leaf senescence, compared to many other crops. Therefore, a better understanding of leaf senescence and developing strategies controlling the progress of leaf senescence in rapeseed is necessary for warranting vegetable oil security. Here we functionally characterized the gene BnaNAM encoding No Apical Meristem (NAM) homologue to identify transcriptional regulation of leaf senescence in rapeseed. A combination of transient and stable expression techniques revealed overexpression of BnaNAM induced ROS production and leaf chlorosis. Quantitative evaluation of up-regulated genes in BnaNAM overexpression lines identified genes related to ROS production (RbohD, RbohF), proteases (βVPE, γVPE, SAG12, SAG15), chlorophyll catabolism (PaO, PPH) and nucleic acid degradation (BFN1) as the putative downstream targets. A dual luciferase-based transcriptional activation assay of selected promoters further confirmed BnaNAM mediated transactivation of promoters of the downstream genes. Finally, an electrophoretic mobility shift assay further confirmed direct binding of BnaNAM to promoters of βVPE, γVPE, SAG12, SAG15 and BFN1. Our results therefore demonstrate a novel role of BnaNAM in leaf senescence.

The membrane associated NAC transcription factors ANAC060 and ANAC040 are functionally redundant in the inhibition of seed dormancy in Arabidopsis thaliana

The NAC family of transcription factors is involved in plant development and various biotic and abiotic stresses. The Arabidopsis thaliana ANAC genes ANAC060, ANAC040, and ANAC089 are highly homologous based on protein and nucleotide sequence similarity. These three genes are predicted to be membrane bound transcription factors (MTFs) containing a conserved NAC domain, but divergent C-terminal regions. The anac060 mutant shows increased dormancy when compared with the wild type. Mutations in ANAC040 lead to higher seed germination under salt stress, and a premature stop codon in ANAC089 Cvi allele results in seeds exhibiting insensitivity to high concentrations of fructose. Thus, these three homologous MTFs confer distinct functions, although all related to germination. To investigate whether the differences in function are caused by a differential spatial or temporal regulation, or by differences in the coding sequence (CDS), we performed swapping experiments in which the promoter and CDS of the three MTFs were exchanged. Seed dormancy and salt and fructose sensitivity analyses of transgenic swapping lines in mutant backgrounds showed that there is functional redundancy between ANAC060 and ANAC040, but not between ANAC060 and ANAC089.

Ectopic Expression of AeNAC83, a NAC Transcription Factor from Abelmoschus esculentus, Inhibits Growth and Confers Tolerance to Salt Stress in Arabidopsis

NAC transcription factors play crucial roles in plant growth, development and stress responses. Previously, we preliminarily identified that the transcription factor AeNAC83 gene was significantly up-regulated under salt stress in okra (Abelmoschus esculentus). Herein, we cloned the nuclear-localized AeNAC83 from okra and identified its possible role in salt stress response and plant growth. The down-regulation of AeNAC83 caused by virus-induced gene silencing enhanced plant sensitivity to salt stress and increased the biomass accumulation of okra seedlings. Meanwhile, AeNAC83-overexpression Arabidopsis lines improved salt tolerance and exhibited many altered phenotypes, including small rosette, short primary roots, and promoted crown roots and root hairs. RNA-seq showed numerous genes at the transcriptional level that changed significantly in the AeNAC83-overexpression transgenic and the wild Arabidopsis with or without NaCl treatment, respectively. The expression of most phenylpropanoid and flavonoid biosynthesis-related genes was largely induced by salt stress. While genes encoding key proteins involved in photosynthesis were almost declined dramatically in AeNAC83-overexpression transgenic plants, and NaCl treatment further resulted in the down-regulation of these genes. Furthermore, DEGs encoding various plant hormone signal pathways were also identified. These results indicate that AeNAC83 is involved in resistance to salt stress and plant growth.

Genome-Wide Identification and Expression Analysis of the NAC Gene Family in Alfalfa Revealed Its Potential Roles in Response to Multiple Abiotic Stresses

NAC (NAM, ATAF1/2, and CUC2) transcription factors compose one of the largest families of plant-specific transcription factors; they are widely involved in plant growth and development and have especially important roles in improving stress resistance in plants. However, NAC gene family members in alfalfa (Medicago sativa L.) have not been systematically identified and analyzed genome-wide due to the complexity of the alfalfa reference genome. In this study, a total of 421 M. sativa NAC genes (MsNACs) were identified from the alfalfa “Xinjiangdaye” reference genome. Basic bioinformatics analysis, including characterization of sequence length, protein molecular weight and genome position and conserved motif analysis, was conducted. Expression analysis showed that 47 MsNACs had tissue-specific expression, and 64 MsNACs were expressed in all tissues. The transcriptomic profiles of the genes were very different, indicating that these MsNACs have various functions in alfalfa growth and development. We identified 25, 42 and 47 MsNACs that respond to cold, drought and salt stress based on transcriptome data analysis and real-time quantitative PCR (RT−qPCR). Furthermore, 22 MsNACs were found to respond to both salt and drought stress, and 15 MsNACs were found to respond to cold, salt and drought stress. The results of this study could provide valuable information for further functional analysis of MsNACs and for the improvement of stress resistance in alfalfa.

Drought resistance of tobacco overexpressing the AfNAC1 gene of Amorpha fruticosa Linn

Plants are often adversely affected by abiotic stresses such as drought, low temperature, and salinity during growth, and plant NAC-like transcription factors are involved in regulating growth and developmental processes in response to stresses such as drought and salinity. In this study, to investigate the function of AfNAC1, a co-expression network of AfNAC1 genes was constructed using gene expression data from the Chinese legume deciduous shrub, Amorpha fruticosa Linn. A 576 bp NAC transcription factor (AfNAC1 gene, MN180266) encoding 191 amino acids was isolated from Amorpha fruticosa seedlings by RT-PCR. qRT-PCR showed that the AfNAC1 gene was expressed in the roots, stems, leaves, and flowers of Amorpha fruticosa. However, drought stress significantly increased root expression, and the AfNAC1 protein was localized in the nucleus by green fluorescence detection. This study analyzed the drought resistance of overexpressing tobacco in depth. Under natural drought stress, the chlorophyll and antioxidant enzyme activities of overexpressing plants were significantly higher than those of wild-type (WT) plants, but the MDA content was lower than that of WT; after rehydration the Fv/Fm values of AfNAC1-overexpressing tobacco recovered faster than those of wild-type tobacco and rapidly reached the control levels; AfNAC1 may be involved in the regulation of the photosystem and indirectly in the regulation of the plant in response to drought stress.

A NAC Transcription Factor from 'Sea Rice 86' Enhances Salt Tolerance by Promoting Hydrogen Sulfide Production in Rice Seedlings

Soil salinity severely threatens plant growth and crop performance. Hydrogen sulfide (H₂S), a plant signal molecule, has been implicated in the regulation of plant responses to salinity stress. However, it is unclear how the transcriptional network regulates H₂S biosynthesis during salt stress response. In this study, we identify a rice NAC (NAM, ATAF and CUC) transcription factor, OsNAC35-like (OsNACL35), from a salt-tolerant cultivar ‘Sea Rice 86′ (SR86) and further show that it may have improved salt tolerance via enhanced H₂S production. The expression of OsNACL35 was significantly upregulated by high salinity and hydrogen peroxide (H₂O₂). The OsNACL35 protein was localized predominantly in the nucleus and was found to have transactivation activity in yeast. The overexpression of OsNACL35 (OsNACL35-OE) in japonica cultivar Nipponbare ramatically increased resistance to salinity stress, whereas its dominant-negative constructs (SUPERMAN repression domain, SRDX) conferred hypersensitivity to salt stress in the transgenic lines at the vegetative stage. Moreover, the quantitative real-time PCR analysis showed that many stress-associated genes were differentially expressed in the OsNACL35-OE and OsNACL35-SRDX lines. Interestingly, the ectopic expression of OsNACL35 triggered a sharp increase in H₂S content by upregulating the expression of a H₂S biosynthetic gene, OsDCD1, upon salinity stress. Furthermore, the dual luciferase and yeast one-hybrid assays indicated that OsNACL35 directly upregulated the expression of OsDCD1 by binding to the promoter sequence of OsDCD1. Taken together, our observations illustrate that OsNACL35 acts as a positive regulator that links H₂S production to salt stress tolerance, which may hold promising utility in breeding salt-tolerant rice cultivar.

RNA-seq analysis reveals the genes/pathways responsible for genetic plasticity of rice to varying environmental conditions on direct-sowing and transplanting

Rice cultivation by transplanting requires plenty of water. It might become a challenging task in future to grow rice by transplanting due to the climatic change, water and labor scarcities. Direct-sown rice (DSR) is emerging as a resource-conserving and climate-smart alternative to transplanted rice (TPR). However, no specific variety has been bred for dry/direct-sown conditions. The present study was undertaken to decipher the molecular basis of genetic plasticity of rice under different planting methods. Comparative RNA-seq analysis revealed a number (6133) of genes exclusively up-regulated in Nagina-22 (N-22) leaf under DSR conditions, compared to that (3538) in IR64 leaf. Several genes up-regulated in N-22 were down-regulated in IR64. Genes for growth-regulation and nutrient-reservoir activities, transcription factors, translational machinery, carbohydrate metabolism, cell cycle/division, and chromatin organization/epigenetic modifications were considerably up-regulated in the leaf of N-22 under DSR conditions. Complementary effects of these factors in rendering genetic plasticity were confirmed by the agronomic/physiological performance of rice cultivar. Thus, growth-regulation/nutrient-reservoir activities, transcription factors, and translational machinery are important molecular factors responsible for the observed genetic plasticity/adaptability of Nagina-22 to different planting methods. This might help to develop molecular markers for DSR breeding, replacing TPR with DSR for better water-productivity, and minimizing greenhouse-gas emission necessary for negative emission agriculture.

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.

PtrMYB120 functions as a positive regulator of both anthocyanin and lignin biosynthetic pathway in a hybrid poplar

Both anthocyanins and lignins are essential secondary metabolites in plant growth and development. Their biosynthesis is metabolically interconnected and diverges in the central metabolite 4-coumaroyl CoA of the phenylpropanoid pathway. Considerable progress has been made in understanding transcriptional regulation of genes involved in lignin and anthocyanin synthesis pathways, but the concerted regulation of these pathways is not yet fully understood. Here, we functionally characterized PtrMYB120, a R2R3-MYB transcription factor from Populus trichocarpa. Overexpression of PtrMYB120 in a hybrid poplar (i.e., 35S::PtrMYB120) was associated with increased anthocyanin (i.e., cyanidin 3-O-glucoside) accumulation and upregulation of anthocyanin biosynthetic genes. However, transgenic poplars with dominant suppression of PtrMYB120 function achieved by fusing the ERF-associated amphiphilic repression motif to PtrMYB120 (i.e., 35S::PtrMYB120-SRDX) had a dramatic decrease in not only anthocyanin but also Klason lignin content with downregulation of both anthocyanin and lignin biosynthetic genes. Indeed, 35S::PtrMYB120-SRDX poplars had irregularly shaped xylem vessels with reduced S-lignin content in stems, which was proportionally related to the level of the introduced PtrMYB120-SRDX gene. Furthermore, protoplast-based transcriptional activation assay using the PtrMYB120-GR system suggested that PtrMYB120 directly regulates genes involved in both anthocyanin and lignin biosynthesis, including chalcone synthase and ferulate-5 hydroxylase. Interestingly, the saccharification efficiency of line #6 of 35S::PtrMYB120-SRDX poplars, which had slightly reduced lignin content with a normal growth phenotype, was dramatically enhanced (>45%) by NaOH treatment. Taken together, our results suggest that PtrMYB120 functions as a positive regulator of both anthocyanin and lignin biosynthetic pathways and can be targeted to enhance saccharification efficiency in woody perennials.

Genome-Wide Investigation of the NAC Transcription Factor Family in Miscanthus sinensis and Expression Analysis Under Various Abiotic Stress

The NAC transcription factor family is deemed to be a large plant-specific gene family that plays important roles in plant development and stress response. Miscanthus sinensis is commonly planted in vast marginal land as forage, ornamental grass, or bioenergy crop which demand a relatively high resistance to abiotic stresses. The recent release of a draft chromosome-scale assembly genome of M. sinensis provided a basic platform for the genome-wide investigation of NAC proteins. In this study, a total of 261 M. sinensis NAC genes were identified and a complete overview of the gene family was presented, including gene structure, conserved motif compositions, chromosomal distribution, and gene duplications. Results showed that gene length, molecular weights (MW), and theoretical isoelectric points (pI) of NAC family were varied, while gene structure and motifs were relatively conserved. Chromosomal mapping analysis found that the M. sinensis NAC genes were unevenly distributed on 19 M. sinensis chromosomes, and the interchromosomal evolutionary analysis showed that nine pairs of tandem duplicates genes and 121 segmental duplications were identified, suggesting that gene duplication, especially segmental duplication, is possibly associated with the amplification of M. sinensis NAC gene family. The expression patterns of 14 genes from M. sinensis SNAC subgroup were analyzed under high salinity, PEG, and heavy metals, and multiple NAC genes could be induced by the treatment. These results will provide a very useful reference for follow-up study of the functional characteristics of NAC genes in the mechanism of stress-responsive and potential roles in the development of M. sinensis.

Regulation of rose petal dehydration tolerance and senescence by RhNAP transcription factor via the modulation of cytokinin catabolism

Petals and leaves share common evolutionary origins but have different phenotypic characteristics, such as the absence of stomata in the petals of most angiosperm species. Plant NAC transcription factor, NAP, is involved in ABA responses and regulates senescence-associated genes, and especially those that affect stomatal movement. However, the regulatory mechanisms and significance of NAP action in senescing astomatous petals is unclear. A major limiting factor is failure of flower opening and accelerated senescence. Our goal is to understand the finely regulatory mechanism of dehydration tolerance and aging in rose flowers. We functionally characterized RhNAP, an AtNAP-like transcription factor gene that is induced by dehydration and aging in astomatous rose petals. Cytokinins (CKs) are known to delay petal senescence and we found that a cytokinin oxidase/dehydrogenase gene 6 (RhCKX6) shares similar expression patterns with RhNAP. Silencing of RhNAP or RhCKX6 expression in rose petals by virus induced gene silencing markedly reduced petal dehydration tolerance and delayed petal senescence. Endogenous CK levels in RhNAP- or RhCKX6-silenced petals were significantly higher than those of the control. Moreover, RhCKX6 expression was reduced in RhNAP-silenced petals. This suggests that the expression of RhCKX6 is regulated by RhNAP. Yeast one-hybrid experiments and electrophoresis mobility shift assays showed that RhNAP binds to the RhCKX6 promoter in heterologous in vivo system and in vitro, respectively. Furthermore, the expression of putative signal transduction and downstream genes of ABA-signaling pathways were also reduced due to the repression of PP2C homolog genes by RhNAP in rose petals. Taken together, our study indicates that the RhNAP/RhCKX6 interaction represents a regulatory step enhancing dehydration tolerance in young rose petals and accelerating senescence in mature petals in a stomata-independent manner.

Ampelopsin Confers Endurance and Rehabilitation Mechanisms in Glycine max cv. Sowonkong under Multiple Abiotic Stresses

The present investigation aims to perceive the effect of exogenous ampelopsin treatment on salinity and heavy metal damaged soybean seedlings (Glycine max L.) in terms of physiochemical and molecular responses. Screening of numerous ampelopsin concentrations (0, 0.1, 1, 5, 10 and 25 μM) on soybean seedling growth indicated that the 1 μM concentration displayed an increase in agronomic traits. The study also determined how ampelopsin application could recover salinity and heavy metal damaged plants. Soybean seedlings were irrigated with water, 1.5% NaCl or 3 mM chosen heavy metals for 12 days. Our results showed that the application of ampelopsin raised survival of the 45-day old salinity and heavy metal stressed soybean plants. The ampelopsin treated plants sustained high chlorophyll, protein, amino acid, fatty acid, salicylic acid, sugar, antioxidant activities and proline contents, and displayed low hydrogen peroxide, lipid metabolism, and abscisic acid contents under unfavorable status. A gene expression survey revealed that ampelopsin application led to the improved expression of GmNAC109, GmFDL19, GmFAD3, GmAPX, GmWRKY12, GmWRKY142, and GmSAP16 genes, and reduced the expression of the GmERF75 gene. This study suggests irrigation with ampelopsin can alleviate plant damage and improve plant yield under stress conditions, especially those including salinity and heavy metals.

Mapping of QTL for agronomic traits using high-density SNPs with an RIL population in maize

BACKGROUND

Genome wide association studies (GWAS) have been widely used to identify QTLs underlying quantitative traits in humans and animals, and they have also become a popular method of mapping QTLs in many crops, including maize. Advances in high-throughput genotyping technologies enable construction of high-density linkage maps using SNP markers.

OBJECTIVES

High-density genetic mapping must precede to find molecular markers associated with a particular trait. The objectives of this study were to (1) construct a high-density linkage map using SNP markers and (2) detect the QTLs for grain yield and quality related traits of the Mo17/KW7 RIL population.

METHODS

In this study, two parental lines, Mo17 (normal maize inbred line) and KW7 (waxy inbred line) and 80 F_7:8 lines in the Mo17/KW7 RIL population were genotyped using the MaizeSNP50 BeadChip, an Illumina BeadChip array of 56,110 maize SNPs. Marker integration and detection of QTLs was performed using the inclusive composite interval mapping (ICIM) method within the QTL IciMapping software.

RESULTS

This study was genotyped using the Illumina MaizeSNP50 BeadChip for maize Mo17/KW7 recombinant inbred line (RIL) population. The 2904 SNP markers were distributed along all 10 maize chromosomes. The total length of the linkage map was 3553.7 cm, with an average interval of 1.22 cm between SNPs. A total of 18 QTLs controlling eight traits were detected in the Mo17/KW7 RIL population. Three QTLs for plant height (PH) were detected on chromosomes 4 and 8 and showed from 16.01% (qPH8) to 19.85% (qPH4a) of phenotypic variance. Five QTLs related to ear height (EH) were identified on chromosomes 3, 4, and 6 and accounted for 3.79% (qEH6) to 27.57% (qEH4b) of phenotypic variance. Five QTLs related to water content (WC) on chromosomes 1, 4, 8, and 9 accounted for 9.55% (qWC8b) to 23.30% (qWC4) of phenotypic variance. One QTL (qAC9) relating to amylose content (AC) on chromosome 9 showed 82.10% of phenotypic variance.

CONCLUSIONS

The high-density linkage map and putative QTLs of the maize RIL population detected in this study can be effectively utilized in waxy and normal maize breeding programs to facilitate the selection process through marker-assisted selection (MAS) breeding programs.

Glyoxalase I-4 functions downstream of NAC72 to modulate downy mildew resistance in grapevine

Glyoxalase I (GLYI) is part of the glyoxalase system; its major function is the detoxification of α-ketoaldehydes, including the potent and cytotoxic methylglyoxal (MG). Methylglyoxal disrupts mitochondrial respiration and increases production of reactive oxygen species (ROS), which also increase during pathogen infection of plant tissues; however, there have been few studies relating the glyoxalase system to the plant pathogen response. We used the promoter of VvGLYI-4 to screen the upstream transcription factors and report a NAC (NAM/ATAF/CUC) domain-containing transcription factor VvNAC72 in grapevine, which is localized to the nucleus. Our results show that VvNAC72 expression is induced by downy mildew, Plasmopara viticola, while the transcript level of VvGLYI-4 decreases. Further analysis revealed that VvNAC72 can bind directly to the promoter region of VvGLYI-4 via the CACGTG element, leading to inhibition of VvGLYI-4 transcription. Stable overexpression of VvNAC72 in grapevine and tobacco showed a decreased expression level of VvGLYI-4 and increased content of MG and ROS, as well as stronger resistance to pathogen stress. Taken together, these results demonstrate that grapevine VvNAC72 negatively modulates detoxification of MG through repression of VvGLYI-4, and finally enhances resistance to downy mildew, at least in part, via the modulation of MG-associated ROS homeostasis through a salicylic acid-mediated defense pathway.

The miR164-GhCUC2-GhBRC1 module regulates plant architecture through abscisic acid in cotton

Branching determines cotton architecture and production, but the underlying regulatory mechanisms remain unclear. Here, we report that the miR164-GhCUC2 (CUP-SHAPED COTYLEDON2) module regulates lateral shoot development in cotton and Arabidopsis. We generated OE-GhCUC2m (overexpression GhCUC2m) and STTM164 (short tandem target mimic RNA of miR164) lines in cotton and heterologous expression lines for gh-miR164, GhCUC2 and GhCUC2m in Arabidopsis to study the mechanisms controlling lateral branching. GhCUC2m overexpression resulted in a short-branch phenotype similar to STTM164. In addition, heterologous expression of GhCUC2m led to decreased number and length of branches compared with wild type, opposite to the effects of the OE-gh-pre164 line in Arabidopsis. GhCUC2 interacted with GhBRC1 and exhibited similar negative regulation of branching. Overexpression of GhBRC1 in the brc1-2 mutant partially rescued the mutant phenotype and decreased branch number. GhBRC1 directly bound to the NCED1 promoter and activated its transcription, leading to local abscisic acid (ABA) accumulation and response. Mutation of the NCED1 promoter disrupted activation by GhBRC1. This finding demonstrates a direct relationship between BRC1 and ABA signalling and places ABA downstream of BRC1 in the control of branching development. The miR164-GhCUC2-GhBRC1-GhNCED1 module provides a clear regulatory axis for ABA signalling to control plant architecture.

LEAFY, a Pioneer Transcription Factor in Plants: A Mini-Review

A subset of eukaryotic transcription factors (TFs) possess the ability to reprogram one cell type into another. Genes important for cellular reprograming are typically located in closed chromatin, which is covered by nucleosomes. Pioneer factors are a special class of TFs that can initially engage their target sites in closed chromatin prior to the engagement with, opening of, or modification of the sites by other factors. Although many pioneer factors are known in animals, a few have been characterized in plants. The TF LEAFY (LFY) acts as a pioneer factor specifying floral fate in Arabidopsis. In response to endogenous and environmental cues, plants produce appropriate floral inducers (florigens). During the vegetative phase, LFY is repressed by the TERMINAL FLOWER 1 (TFL1)-FD complex, which functions as a floral inhibitor, or anti-florigen. The florigen FLOWERING LOCUS T (FT) competes with TFL1 to prevent the binding of the FD TF to the LFY locus. The resulting FT-FD complex functions as a transient stimulus to activate its targets. Once LFY has been transcribed in the appropriate spatiotemporal manner, LFY binds to nucleosomes in closed chromatin regions. Subsequently, LFY opens the chromatin by displacing H1 linker histones and recruiting the SWI/SNF chromatin-remodeling complex. Such local changes permit the binding of other TFs, leading to the expression of the floral meristem identity gene APETALA1. This mini-review describes the latest advances in our understanding of the pioneer TF LFY, providing insight into the establishment of gene expression competence through the shaping of the plant epigenetic landscape.

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).

The biotechnological importance of the plant-specific NAC transcription factor family in crop improvement

Climate change, malnutrition, and food insecurity are the inevitable challenges being faced by the agriculture sector today. Plants are susceptible to extreme temperatures during the crucial phases of flowering and seed development, and elevated carbon levels also lead to yield losses. Productivity is also affected by floods and droughts. Therefore, increasing plant yield and stress tolerance are the priorities to be met through novel biotechnological interventions. The contributions of NAC genes towards enhancing plant survivability under stress is well known. Here we focus on the potential of NAC genes in the regulation of abiotic stress tolerance, secondary cell wall synthesis, lateral root development, yield potential, seed size and biomass, ROS signaling, leaf senescence, and programmed cell death. Once naturally tolerant candidate NAC genes have been identified, and the nature of their association with growth and fitness against multi-environmental stresses has been determined, they can be exploited for building inherent tolerance in future crops via transgenic technologies. An update on the latest developments is provided in this review, which summarizes the current understanding of the roles of NAC in the establishment of various stress-adaptive mechanisms in model and food crop plants.

Gene co-expression network analysis reveals key pathways and hub genes in Chinese cabbage (Brassica rapa L.) during vernalization

BACKGROUND

Vernalization is a type of low temperature stress used to promote rapid bolting and flowering in plants. Although rapid bolting and flowering promote the reproduction of Chinese cabbages (Brassica rapa L. ssp. pekinensis), this process causes their commercial value to decline. Clarifying the mechanisms of vernalization is essential for its further application. We performed RNA sequencing of gradient-vernalization in order to explore the reasons for the different bolting process of two Chinese cabbage accessions during vernalization.

RESULTS

There was considerable variation in gene expression between different-bolting Chinese cabbage accessions during vernalization. Comparative transcriptome analysis and weighted gene co-expression network analysis (WGCNA) were performed for different-bolting Chinese cabbage during different vernalization periods. The biological function analysis and hub gene annotation of highly relevant modules revealed that shoot system morphogenesis and polysaccharide and sugar metabolism caused early-bolting 'XBJ' to bolt and flower faster; chitin, ABA and ethylene-activated signaling pathways were enriched in late-bolting 'JWW'; and leaf senescence and carbohydrate metabolism enrichment were found in the two Chinese cabbage-related modules, indicating that these pathways may be related to bolting and flowering. The high connectivity of hub genes regulated vernalization, including MTHFR2, CPRD49, AAP8, endoglucanase 10, BXLs, GATLs, and WRKYs. Additionally, five genes related to flower development, BBX32 (binds to the FT promoter), SUS1 (increases FT expression), TSF (the closest homologue of FT), PAO and NAC029 (plays a role in leaf senescence), were expressed in the two Chinese cabbage accessions.

CONCLUSION

The present work provides a comprehensive overview of vernalization-related gene networks in two different-bolting Chinese cabbages during vernalization. In addition, the candidate pathways and hub genes related to vernalization identified here will serve as a reference for breeders in the regulation of Chinese cabbage production.

Overexpression of MusaSNAC1 improves shoot proliferation in transgenic banana lines

Augmenting shoot multiplication through genetic engineering is an emerging biotechnological application desirable in optimizing regeneration of genetically modified plants on selection medium and rapid clonal propagation of elite cultivars. Here, we report the improved shoot multiplication in transgenic banana lines with overexpression of MusaSNAC1, a drought-associated NAC transcription factor in banana. Overexpression of MusaSNAC1 induces hypersensitivity of transgenic banana lines toward 6-benzylaminopurine ensuing higher shoot number on different concentrations of 6-benzylaminopurine. Altered transcript levels of multiple genes involved in auxin signaling (Aux/IAA and ARFs) and cytokinin signaling pathways (ARRs) in banana plants overexpressing MusaSNAC1 corroborate the hypersensitivity of transgenic banana plants toward 6-benzylaminopurine. Modulation in expression of ARRs reported to be involved in ABA-hypersensitivity and closure of stomatal aperture correlates with the function of MusaSNAC1 as a drought-responsive NAC transcription factor. Present study suggests a prospective cross talk between shoot multiplication and drought responses coordinated by MusaSNAC1 in banana plants.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02744-5.

Genome-wide identification, characterization, and expression analysis of the NAC transcription factor family in orchardgrass (Dactylis glomerata L.)

Background

Orchardgrass (Dactylis glomerata L.) is one of the most important cool-season perennial forage grasses that is widely cultivated in the world and is highly tolerant to stressful conditions. However, little is known about the mechanisms underlying this tolerance. The NAC (NAM, ATAF1/2, and CUC2) transcription factor family is a large plant-specific gene family that actively participates in plant growth, development, and response to abiotic stress. At present, owing to the absence of genomic information, NAC genes have not been systematically studied in orchardgrass. The recent release of the complete genome sequence of orchardgrass provided a basic platform for the investigation of DgNAC proteins.

Results

Using the recently released orchardgrass genome database, a total of 108 NAC (DgNAC) genes were identified in the orchardgrass genome database and named based on their chromosomal location. Phylogenetic analysis showed that the DgNAC proteins were distributed in 14 subgroups based on homology with NAC proteins in Arabidopsis, including the orchardgrass-specific subgroup Dg_NAC. Gene structure analysis suggested that the number of exons varied from 1 to 15, and multitudinous DgNAC genes contained three exons. Chromosomal mapping analysis found that the DgNAC genes were unevenly distributed on seven orchardgrass chromosomes. For the gene expression analysis, the expression levels of DgNAC genes in different tissues and floral bud developmental stages were quite different. Quantitative real-time PCR analysis showed distinct expression patterns of 12 DgNAC genes in response to different abiotic stresses. The results from the RNA-seq data revealed that orchardgrass-specific NAC exhibited expression preference or specificity in diverse abiotic stress responses, and the results indicated that these genes may play an important role in the adaptation of orchardgrass under different environments.

Conclusions

In the current study, a comprehensive and systematic genome-wide analysis of the NAC gene family in orchardgrass was first performed. A total of 108 NAC genes were identified in orchardgrass, and the expression of NAC genes during plant growth and floral bud development and response to various abiotic stresses were investigated. These results will be helpful for further functional characteristic descriptions of DgNAC genes and the improvement of orchardgrass in breeding programs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07485-6.

Interactions between ScNAC23 and ScGAI regulate GA-mediated flowering and senescence in sugarcane

Control of gene transcription is crucial to regulate plant growth and development events, such as flowering, leaf senescence, and seed germination. Here we identified a NAC transcription factor (ScNAC23) isolated from sugarcane (cv. ROC22). Analysis by qRT-PCR indicated that ScNAC23 expression was strongly induced in mature leaves and flowering varieties and was also responsive to exogenous treatment with the hormone gibberellin (GA). Ectopic expression of ScNAC23 in Arabidopsis accelerated bolting, flowering, and leaf senescence compared to wild type plants. Furthermore, Arabidopsis overexpressed ScNAC23 were more sensitive to GA than the wild type, and exogenous GA significantly accelerated flowering and senescence in the ScNAC23-overexpressed ones. A direct interaction between ScNAC23 and ScGAI, an inhibitor of GA signaling, was confirmed by yeast-two hybrid, bimolecular fluorescence complementation, and GST-pull down assay. The putative GA-ScNAC23-LFY/SAGs regulator module might provide a new sight into the molecular action of GA to accelerating flowering and leaf senescence in sugarcane.

The soybean GmNFY-B1 transcription factor positively regulates flowering in transgenic Arabidopsis

Nuclear Factor Y (NF-Y) gene family regulates numbers of flowering processes. Two independent transgenic Arabidopsis lines overexpressing (OX) GmNFY-B1 and GmNFYB1-GR (GmNFYB1 fused with the glucocorticoid receptor) were used to investigate the function of NFY-B1 in flowering. Furthermore, GmNFYB1-GR lines were chemically treated with dexamethasone (Dex, synthetic steroid hormone), cycloheximide (Cyc, an inhibitor of protein biosynthesis), and ethanol to examine their effects on different flowering related marker genes. Our results indicated that the transgenic lines produced longer hypocotyl lengths and had fewer numbers of rosette leaves compared to the wild-type and nf-yb1 mutant plants under both long and short-day (LD and SD) conditions. The qRT-PCR assays revealed that transcript levels of all flowering time regulating genes, i.e. SOC, FLC, FT, TSF, LFY, GI2, AGL, and FCA showed higher transcript abundance in lines OX GmNFYB1-GR. However, FT and GI genes showed higher transcript levels under Dex and Dex/Cyc treatments compared to Cyc and ethanol. Additionally, 24 differentially expressed genes were identified and verified through RNA-seq and RT-qPCR in GmNF-YB1-GR lines under Cyc and Dex/Cyc treatments from which 14 genes were up-regulated and 10 were down-regulated. These genes are involved in regulatory functions of circadian rhythm, regulation of flower development in photoperiodic, and GA pathways. The overexpression of GmNF-YB1 and GmNF-YB1-GR promote flowering through the higher expression of flowering-related genes. Further GmNF-YB1 and its attachment with the GR receptor can regulate its target genes under Dex/Cyc treatment and might act as flowering inducer under LD and SD conditions.

Structure-function relationship of Gossypium hirsutum NAC transcription factor, GhNAC4 with regard to ABA and abiotic stress responses

Our previous study demonstrated that the expression of GhNAC4, a NAC transcription factor from cotton, was induced by abiotic stresses and abscisic acid (ABA). In the present study, we investigated the molecular mechanisms underlying ABA and stress response of GhNAC4. Overexpression of GhNAC4 in transgenic tobacco conferred tolerance to salinity and drought treatments with associated enhanced expression of several stress-responsive marker genes. GhNAC4 is a protein that is translocated to the nucleus where it exhibits transcriptional activation property and also forms homo-dimers. In this study, we also investigated the domains essential for the biochemical functions of GhNAC4. We developed transgenic tobacco plants overexpressing the GhNAC4 NAC-domain and the transcriptional regulatory (TR) domain separately. NAC-domain transgenics showed hypersensitivity to exogenous ABA while TR-domain transgenics exhibited reduced sensitivity. Abiotic stress assays indicated that transgenic plants expressing both the domains separately were more tolerant than wild type plants with the NAC-domain transgenics showing increased tolerance as compared to TR-domain transgenics. Expression analysis revealed that various stress-responsive genes were upregulated in both NAC-domain and TR-domain transgenics under salinity and drought treatments. These results suggest that the stress tolerance ability of GhNAC4 is associated with both the component domains while the ABA responsiveness is largely associated with N-terminal NAC-domain.

Comparative transcriptome analysis of gynoecious and monoecious inflorescences reveals regulators involved in male flower development in the woody perennial plant Jatropha curcas

ABCE model genes along with genes related to GA biosynthesis and auxin signalling may play significant roles in male flower development in Jatropha curcas. Flowering plants exhibit extreme reproductive diversity. Jatropha curcas, a woody plant that is promising for biofuel production, is monoecious. Here, two gynoecious Jatropha mutants (bearing only female flowers) were used to identify key genes involved in male flower development. Using comparative transcriptome analysis, we identified 17 differentially expressed genes (DEGs) involved in floral organ development between monoecious plants and the two gynoecious mutants. Among these DEGs, five floral organ identity genes, Jatropha AGAMOUS, PISTILLATA, SEPALLATA 2-1 (JcSEP2-1), JcSEP2-2, and JcSEP3, were downregulated in ch mutant inflorescences; two gibberellin (GA) biosynthesis genes, Jatropha GA REQUIRING 1 and GIBBERELLIN 3-OXIDASE 1, were downregulated in both the ch and g mutants; and two genes involved in the auxin signalling pathway, Jatropha NGATHA1 and STYLISH1, were downregulated in the ch mutant. Furthermore, four hub genes involved in male flower development, namely Jatropha SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE 1, CRYPTOCHROME 2, SUPPRESSOR OF OVEREXPRESSION OF CO 1 and JAGGED, were identified using weighted gene correlation network analysis. These results suggest that floral organ identity genes and genes involved in GA biosynthesis and auxin signalling may participate in male flower development in Jatropha. This study will contribute to understanding sex differentiation in woody perennial plants.

GmNAC81 Inversely Modulates Leaf Senescence and Drought Tolerance

Glycine max NAC81 (GmNAC81) is a downstream effector of the DCD/NRP-mediated cell death signaling, which interacts with GmNAC30 to fully induce the caspase 1-like vacuolar processing enzyme (VPE) expression, the executioner of the cell death program. GmNAC81 has been previously shown to positively modulate leaf senescence via the NRP/GmNAC81/VPE signaling module. Here, we examined the transcriptome induced by GmNAC81 overexpression and leaf senescence and showed that GmNAC81 further modulates leaf senescence by regulating an extensive repertoire of functionally characterized senescence-associated genes (SAGs). Because the NRP/GmNAC81/VPE signaling circuit also relays stress-induced cell death signals, we examined the effect of GmNAC81 overexpression in drought responses. Enhanced GmNAC81 expression in the transgenic lines increased sensitivity to water deprivation. Under progressive drought, the GmNAC81-overexpressing lines displayed severe leaf wilting, a larger and faster decline in leaf Ψw, relative water content (RWC), photosynthesis rate, stomatal conductance, and transpiration rate, in addition to higher Ci/Ca and lower Fm/Fv ratios compared to the BR16 control line. Collectively, these results indicate that the photosynthetic activity and apparatus were more affected by drought in the transgenic lines. Consistent with hypersensitivity to drought, chlorophyll loss, and lipid peroxidation were higher in the GmNAC81-overexpressing lines than in BR16 under dehydration. In addition to inducing VPE expression, GmNAC81 overexpression uncovered the regulation of typical drought-responsive genes. In particular, key regulators and effectors of ABA signaling were suppressed by GmNAC81 overexpression. These results suggest that GmNAC81 may negatively control drought tolerance not only via VPE activation but also via suppression of ABA signaling.