An Arabidopsis homeodomain transcription factor gene, HOS9, mediates cold tolerance through a CBF-independent pathway

Identification of the WRKY gene family in Bergenia purpurascens and functional analysis of BpWRKY13 under cold stress

Bergenia purpurascens, a medicinal alpine plant, exhibits remarkable stress resilience. WRKY transcription factors are central regulators of plant stress responses, yet their family in B. purpurascens remains uncharacterized. Here, we identified 57 BpWRKY genes from B. purpurascens transcriptome data. Expression analysis revealed 11 BpWRKY genes differentially expressed under cold stress, with BpWRKY13 showing the strongest induction. To investigate its function, we overexpressed BpWRKY13 in Arabidopsis thaliana. Transgenic plants displayed significantly enhanced cold tolerance, evidenced by reduced leaf damage, increased survival, and elevated accumulation of proline and soluble proteins. Furthermore, transgenic plants exhibited increased activity of antioxidant enzymes and upregulation of cold-responsive genes. These findings indicate that BpWRKY13 confers cold tolerance by promoting osmoprotection and activating antioxidant defense mechanisms. This study provides a crucial foundation for understanding the BpWRKY gene family and highlights BpWRKY13 as a key regulator of cold resistance in B. purpurascens.

Transcriptional dynamics and functions of WUSCHEL-related homeobox (WOX) genes from Ginkgo biloba in tissue culture

BACKGROUND

In vitro regeneration presents significant challenges for the propagation and genetic improvement of most woody plants, particularly gymnosperms. The WUSCHEL-related homeobox (WOX) genes are known to play vital roles as growth regulators in tissue culture regeneration in several plant species. However, the specific functions of WOX genes in the regeneration processes of gymnosperms had not been previously elucidated. This study aims to systematically identify and analyze the WOX gene family in Ginkgo biloba to understand its potential role in tissue culture regeneration.

RESULTS

Thirteen WOX genes from Ginkgo biloba, designated as GbWUS and GbWOXs, were systematically identified. Phylogenetic analysis revealed the presence of nine genes in the WUSCHEL (WUS) clade, one in the intermediate clade, and three in the ancient clade. Transcriptome analysis indicated tissue-specific expression of seven GbWOXs, with two gymnosperm-specific GbWOXs characterized by extra-long introns exhibiting constitutive expression. Further investigation through Ginkgo tissue culture indicated that GbWOX2 was specifically expressed in embryos and facilitated callus induction, while GbWOX3A showed preferential expression during the early stages of embryo and callus development. Co-expression and Gene Ontology (GO) enrichment analyses suggested interactions and functional roles among GbWOXs. Three genes (GbWOX1, GbWOX2, and GbWOX3A) were then cloned and transformed into poplar and/or tobacco. Overexpression of GbWOX2 resulted in larger and denser callus formation, whereas GbWOX3A effectively enhanced shoot regeneration and noticeably increased the rate of adventitious shoot induction.

CONCLUSIONS

This study provides the first comprehensive analysis of the WOX gene family in Ginkgo biloba and highlights its significant role in tissue culture regeneration. The findings suggest that specific GbWOXs are critical for embryo development and callus regeneration, which provides the foundation for the establishment of effective tissue culture systems in Ginkgo. Moreover, this research contributes valuable insights that could be beneficial for improving propagation techniques and genetic studies in other forest trees, especially within the gymnosperm group.

Identification and Characterization of WOX Gene Family in Flax (Linum usitatissimum L.) and Its Role Under Abiotic Stress

The WOX (WUSCHEL-related homeobox) gene family plays pivotal roles in plant growth, development, and responses to biotic/abiotic stresses. Flax (Linum usitatissimum L.), a globally important oilseed and fiber crop, lacks a comprehensive characterization of its WOX family. Here, 18 LuWOX genes were systematically identified in the flax genome through bioinformatics analyses. Phylogenetic classification grouped these genes into three clades: Ancient, Intermediate, and WUS Clades, with members within the same clade exhibiting conserved exon-intron structures and motif compositions. Promoter analysis revealed abundant cis-acting elements associated with hormone responses (MeJA, abscisic acid) and abiotic stress adaptation (anaerobic induction, drought, low temperature). Segmental duplication events (nine gene pairs) contributed significantly to LuWOX family expansion. Protein-protein interaction networks implicated several LuWOX proteins in stress-responsive pathways. Expression profiling demonstrated that most LuWOX genes were highly expressed in 5-day-post-anthesis (DPA) flowers and embryonic tissues. qRT-PCR validation further uncovered distinct expression patterns of LuWOX genes under cold, drought, and salt stresses. This study established a foundational framework for leveraging LuWOX genes to enhance stress tolerance in flax breeding and functional genomics.

PhNH10 Suppresses Low Temperature Tolerance in Petunia Through the Abscisic Acid-Dependent Pathway

Low-temperature stress limits plant growth, and reduces aesthetics of many ornamental plants. Plants have developed different adaptive mechanisms to cope with low-temperature stress, in which NAC transcription factor family members playing an important role in low-temperature tolerance. However, their roles in petunia in response to low temperature are still largely unknown. Here, we found that a NAC transcription factor, namely, PhNH10, negatively regulates low-temperature response in petunia. PhNH10-silenced and -CRISPR/Cas9 mutant plants displayed higher survival rate, anthocyanin content and abscisic acid concentration than PhNH10-overexpression and wild-type plants under low-temperature condition. PhNH10 can directly bind to the PhABA8ox promoter to active its expression, which further promotes the abscisic acid catabolism, while silencing of PhABA8ox increased the ABA concentration and low-temperature tolerance. In addition, PhNH10 interact with a low-temperature-related E2 ubiquitin-conjugating enzyme, PhUBC2-1, which in turn inhibited the binding capacity of PhNH10 on PhABA8ox promoter. Our research has elucidated an extensive mechanistic network underlying the PhNH10-mediated regulation of low-temperature response in petunia. This finding not only presents a new viewpoint in understanding the low-temperature tolerance mechanisms but also delineates a promising pathway for transgenic petunia with improved low-temperature resistance.

Molecular and Physiological Responses of Plants that Enhance Cold Tolerance

Low-temperature stress, including chilling and freezing injuries, significantly impacts plant growth in tropical and temperate regions. Plants respond to cold stress by activating mechanisms that enhance freezing tolerance, such as regulating photosynthesis, metabolism, and protein pathways and producing osmotic regulators and antioxidants. Membrane stability is crucial, with cold-resistant plants exhibiting higher lipid unsaturation to maintain fluidity and normal metabolism. Low temperatures disrupt reactive oxygen species (ROS) metabolism, leading to oxidative damage, which is mitigated by antioxidant defenses. Hormonal regulation, involving ABA, auxin, gibberellins, and others, further supports cold adaptation. Plants also manage osmotic balance by accumulating osmotic regulators like proline and sugars. Through complex regulatory pathways, including the ICE1-CBF-COR cascade, plants optimize gene expression to survive cold stress, ensuring adaptability to freezing conditions. This study reviews the recent advancements in genetic engineering technologies aimed at enhancing the cold resistance of agricultural crops. The goal is to provide insights for further improving plant cold tolerance and developing new cold-tolerant varieties.

The Identification and Characterization of WOX Family Genes in Coffea arabica Reveals Their Potential Roles in Somatic Embryogenesis and the Cold-Stress Response

WUSCHEL-related homeobox (WOX) genes play significant roles in plant development and stress responses. Difficulties in somatic embryogenesis are a significant constraint on the uniform seedling production and genetic modification of Coffea arabica, hindering efforts to improve coffee production in Yunnan, China. This study comprehensively analyzed WOX genes in three Coffea species. A total of 23 CaWOXs, 12 CcWOXs, and 10 CeWOXs were identified. Transcriptomic profile analysis indicated that about half of the CaWOX genes were actively expressed during somatic embryogenesis. The most represented CaWOXs were CaWOX2a, CaWOX2b, CaWOX8a, and CaWOX8b, which are suggested to promote the induction and development of the embryogenic callus, whereas CaWOX13a and CaWOX13b are suggested to negatively impact these processes. Co-expression analysis revealed that somatic embryogenesis-related CaWOXs were co-expressed with genes involved in embryo development, post-embryonic development, DNA repair, DNA metabolism, phenylpropanoid metabolism, secondary metabolite biosynthesis, and several epigenetic pathways. In addition, qRT-PCR showed that four WOX genes responded to cold stress. Overall, this study offers valuable insights into the functions of CaWOX genes during somatic embryogenesis and under cold stress. The results suggest that certain WOX genes play distinct regulatory roles during somatic embryogenesis, meriting further functional investigation. Moreover, the cold-responsive genes identified here are promising candidates for further molecular analysis to assess their potential to enhance cold tolerance.

Engineering cold resilience: implementing gene editing tools for plant cold stress tolerance

MAIN CONCLUSION

This paper highlights the need for innovative approaches to enhance cold tolerance. It underscores how genome-editing tools can deepen our understanding of genes involved in cold stress. Cold stress is a significant abiotic factor in high-altitude regions, adversely affecting plant growth and limiting crop productivity. Plants have evolved various mechanisms in response to low temperatures that enable resistance at both physiological and molecular levels during chilling and freezing stress. Several cold-inducible genes have been isolated and characterized, with most playing key roles in providing tolerance against low-temperature stress. However, many plants fail to survive at low temperatures due to the absence of cold acclimatization mechanisms. Conventional breeding techniques, such as inter-specific or inter-genic hybridization, have had limited effectiveness in enhancing the cold resistance of essential crops. Thus, it is crucial to develop crops with improved adaptability, high yields and resistance to cold stress using advanced genomic approaches. The current availability of gene editing tools offers the opportunity to introduce targeted modifications in plant genomes efficiently, thereby developing cold-tolerant varieties. This review discusses advancements in gene editing tools, including zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)/Cas12a(Cpf1), prime editing (PE) and retron library recombineering (RLR). We focus specifically on the CRISPR/Cas system, which has garnered significant attention in recent years as a groundbreaking tool for genome editing across various species. These techniques will enhance our understanding of molecular interactions under low-temperature stress response and highlight the progress of genome editing in designing future climate-resilient crops.

Plant Growth Regulators: An Overview of WOX Gene Family

The adaptation of plants to land requires sophisticated biological processes and signaling. Transcription factors (TFs) regulate several cellular and metabolic activities, as well as signaling pathways in plants during stress and growth and development. The WUSCHEL-RELATED HOMEOBOX (WOX) genes are TFs that are part of the homeodomain (HD) family, which is important for the maintenance of apical meristem, stem cell niche, and other cellular processes. The WOX gene family is divided into three clades: ancient, intermediate, and modern (WUS) based on historical evolution linkage. The number of WOX genes in the plant body increases as plants grow more complex and varies in different species. Numerous research studies have discovered that the WOX gene family play a role in the whole plant's growth and development, such as in the stem, embryo, root, flower, and leaf. This review comprehensively analyzes roles of the WOX gene family across various plant species, highlighting the evolutionary significance and potential biotechnological applications in stress resistance and crop improvement.

A WUSCHEL-related homeobox transcription factor, SlWOX4, negatively regulates drought tolerance in tomato

KEY MESSAGE

CRISPR/Cas9-mediated knockout of SlWOX4 gene in tomato enhances tolerance to drought stress. Drought stress is one of the major abiotic factors that seriously affects plant growth and crop yield. WUSCHEL-related homeobox (WOX) transcription factors are involved in plant growth, development and stress response. However, little is known about the role of WOX genes in drought tolerance in tomato. Here, SlWOX4, a member of the WOX family in tomato, was functionally characterized in mediating drought tolerance. SlWOX4 was homologous to Nicotiana tabacum NtWOX4 with a conserved HD domain, and was localized in the nucleus. SlWOX4 was significantly down-regulated by drought and abscisic acid (ABA) treatments. The loss-of-function mutations of SlWOX4 produced using the CRISPR-Cas9 system in tomato improved drought tolerance by reducing water loss rate and enhancing stomatal closure. In addition, the wox4 lines exhibited reduced accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA), increased antioxidant enzyme activity, proline contents and ABA contents under drought stress. Moreover, gene editing of SlWOX4 in tomato enhanced drought tolerance by regulating the expression of genes encoding antioxidants and ABA signaling molecules. In summary, SlWOX4 gene might negatively regulate drought stress tolerance in tomato and has great potential as a drought-resistant crop-breeding target genes.

Recent Insights into the Physio-Biochemical and Molecular Mechanisms of Low Temperature Stress in Tomato

Climate change has emerged as a crucial global issue that significantly threatens the survival of plants. In particular, low temperature (LT) is one of the critical environmental factors that influence plant morphological, physiological, and biochemical changes during both the vegetative and reproductive growth stages. LT, including abrupt drops in temperature, as well as winter conditions, can cause detrimental effects on the growth and development of tomato plants, ranging from sowing, transplanting, truss appearance, flowering, fertilization, flowering, fruit ripening, and yields. Therefore, it is imperative to understand the comprehensive mechanisms underlying the adaptation and acclimation of tomato plants to LT, from the morphological changes to the molecular levels. In this review, we discuss the previous and current knowledge of morphological, physiological, and biochemical changes, which contain vegetative and reproductive parameters involving the leaf length (LL), plant height (PH) stem diameter (SD), fruit set (FS), fruit ripening (FS), and fruit yield (FY), as well as photosynthetic parameters, cell membrane stability, osmolytes, and ROS homeostasis via antioxidants scavenging systems during LT stress in tomato plants. Moreover, we highlight recent advances in the understanding of molecular mechanisms, including LT perception, signaling transduction, gene regulation, and fruit ripening and epigenetic regulation. The comprehensive understanding of LT response provides a solid basis to develop the LT-resistant varieties for sustainable tomato production under the ever-changing temperature fluctuations.

Genome-wide prediction and functional analysis of WOX genes in blueberry

BACKGROUND

WOX genes are a class of plant-specific transcription factors. The WUSCHEL-related homeobox (WOX) family is a member of the homeobox transcription factor superfamily. Previous studies have shown that WOX members play important roles in plant growth and development. However, studies of the WOX gene family in blueberry plants have not been reported.

RESULTS

In order to understand the biological function of the WOX gene family in blueberries, bioinformatics were used methods to identify WOX gene family members in the blueberry genome, and analyzed the basic physical and chemical properties, gene structure, gene motifs, promoter cis-acting elements, chromosome location, evolutionary relationships, expression pattern of these family members and predicted their functions. Finally, 12 genes containing the WOX domain were identified and found to be distributed on eight chromosomes. Phylogenetic tree analysis showed that the blueberry WOX gene family had three major branches: ancient branch, middle branch, and WUS branch. Blueberry WOX gene family protein sequences differ in amino acid number, molecular weight, isoelectric point and hydrophobicity. Predictive analysis of promoter cis-acting elements showed that the promoters of the VdWOX genes contained abundant light response, hormone, and stress response elements. The VdWOX genes were induced to express in both stems and leaves in response to salt and drought stress.

CONCLUSIONS

Our results provided comprehensive characteristics of the WOX gene family and important clues for further exploration of its role in the growth, development and resistance to various stress in blueberry plants.

WOX2 functions redundantly with WOX1 and WOX4 to positively regulate seed germination in Arabidopsis

MAIN CONCLUSION

WOX family gene WOX2 is highly expressed during seed development, which functions redundantly with WOX1 and WOX4 to positively regulate seed germination. WOX (WUSCHEL-related homeobox) is a family of transcription factors in plants. They play essential roles in the regulation of plant growth and development, but their function in seed germination is not well understood. In this report, we show that WOX1, WOX2, and WOX4 are close homologues in Arabidopsis. WOX2 has a redundant function with WOX1 and WOX4, respectively, in seed germination. WOX2 is highly expressed during seed development, from the globular embryonic stage to mature dry seeds, and its expression is decreased after germination. Loss of function single mutant wox2, and double mutants wox1 wox2 and wox2 wox4-1 show decreased germination speed. WOX2 and WOX4 are essential for hypocotyl-radicle zone elongation during germination, potentially by promoting the expression of cell wall-related genes. We also found that WOX2 and WOX4 regulate germination through the gibberellin (GA) pathway. These results suggest that WOX2 and WOX4 integrate the GA pathway and downstream cell wall-related genes during germination.

Identification and Expression Patterns of WOX Transcription Factors under Abiotic Stresses in Pinus massoniana

WUSCHEL-related homeobox (WOX) transcription factors (TFs) play a crucial role in regulating plant development and responding to various abiotic stresses. However, the members and functions of WOX proteins in Pinus massoniana remain unclear. In this study, a total of 11 WOX genes were identified, and bioinformatics methods were used for preliminary identification and analysis. The phylogenetic tree revealed that most PmWOXs were distributed in ancient and WUS clades, with only one member found in the intermediate clade. We selected four highly conserved WOX genes within plants for further expression analysis. These genes exhibited expressions across almost all tissues, while PmWOX2, PmWOX3, and PmWOX4 showed high expression levels in the callus, suggesting their potential involvement in specific functions during callus development. Expression patterns under different abiotic stresses indicated that PmWOXs could participate in resisting multiple stresses in P. massoniana. The identification and preliminary analysis of PmWOXs lay the foundation for further research on analyzing the resistance molecular mechanism of P. massoniana to abiotic stresses.

CsBPC2 is essential for cucumber survival under cold stress

Cold stress affects the growth and development of cucumbers. Whether the BPC2 transcription factor participates in cold tolerance and its regulatory mechanism in plants have not been reported. Here, we used wild-type (WT) cucumber seedlings and two mutant Csbpc2 lines as materials. The underlying mechanisms were studied by determining the phenotype, physiological and biochemical indicators, and transcriptome after cold stress. The results showed that CsBPC2 knockout reduced cucumber cold tolerance by increasing the chilling injury index, relative electrical conductivity and malondialdehyde (MDA) content and decreasing antioxidant enzyme activity. We then conducted RNA sequencing (RNA-seq) to explore transcript-level changes in Csbpc2 mutants. A large number of differentially expressed genes (1032) were identified and found to be unique in Csbpc2 mutants. However, only 489 down-regulated genes related to the synthesis and transport of amino acids and vitamins were found to be enriched through GO analysis. Moreover, both RNA-seq and qPT-PCR techniques revealed that CsBPC2 knockout also decreased the expression of some key cold-responsive genes, such as CsICE1, CsCOR413IM2, CsBZR1 and CsBZR2. These results strongly suggested that CsBPC2 knockout not only affected cold function genes but also decreased the levels of some key metabolites under cold stress. In conclusion, this study reveals for the first time that CsBPC2 is essential for cold tolerance in cucumber and provides a reference for research on the biological function of BPC2 in other plants.

Characterization and expression profiles of WUSCHEL-related homeobox (WOX) gene family in cultivated alfalfa (Medicago sativa L.)

The WUSCHEL-related homeobox (WOX) family members are plant-specific transcriptional factors, which function in meristem maintenance, embryogenesis, lateral organ development, as well as abiotic stress tolerance. In this study, 14 MsWOX transcription factors were identified and comprehensively analyzed in the cultivated alfalfa cv. Zhongmu No.1. Overall, 14 putative MsWOX members containing conserved structural regions were clustered into three clades according to phylogenetic analysis. Specific expression patterns of MsWOXs in different tissues at different levels indicated that the MsWOX genes play various roles in alfalfa. MsWUS, MsWOX3, MsWOX9, and MsWOX13-1 from the three subclades were localized in the nucleus, among which, MsWUS and MsWOX13-1 exhibited strong self-activations in yeast. In addition, various cis-acting elements related to hormone responses, plant growth, and stress responses were identified in the 3.0 kb promoter regions of MsWOXs. Expression detection of separated shoots and roots under hormones including auxin, cytokinin, GA, and ABA, as well as drought and cold stresses, showed that MsWOX genes respond to different hormones and abiotic stress treatments. Furthermore, transcript abundance of MsWOX3, and MsWOX13-2 were significantly increased after rhizobia inoculation. This study presented comprehensive data on MsWOX transcription factors and provided valuable insights into further studies of their roles in developmental processes and abiotic stress responses in alfalfa.

Genome-Wide Analysis of WUSCHEL-Related Homeobox Gene Family in Sacred Lotus (Nelumbo nucifera)

WUSCHEL-related homeobox (WOX) is a plant-specific transcription factor (TF), which plays an essential role in the regulation of plant growth, development, and abiotic stress responses. However, little information is available on the specific roles of WOX TFs in sacred lotus (Nelumbo nucifera), which is a perennial aquatic plant with important edible, ornamental, and medicinal values. We identified 15 WOX TFs distributing on six chromosomes in the genome of N. nucifera. A total of 72 WOX genes from five species were divided into three clades and nine subclades based on the phylogenetic tree. NnWOXs in the same subclades had similar gene structures and conserved motifs. Cis-acting element analysis of the promoter regions of NnWOXs found many elements enriched in hormone induction, stress responses, and light responses, indicating their roles in growth and development. The Ka/Ks analysis showed that the WOX gene family had been intensely purified and selected in N. nucifera. The expression pattern analysis suggested that NnWOXs were involved in organ development and differentiation of N. nucifera. Furthermore, the protein-protein interaction analysis showed that NnWOXs might participate in the growth, development, and metabolic regulation of N. nucifera. Taken together, these findings laid a foundation for further analysis of NnWOX functions.

Mdm-miR160-MdARF17-MdWRKY33 module mediates freezing tolerance in apple

Apple (Malus domestica) trees are vulnerable to freezing temperatures. Cold resistance in woody perennial plants can be improved through biotechnological approaches. However, genetic engineering requires a thorough understanding of the molecular mechanisms of the tree's response to cold. In this study, we demonstrated that the Mdm-miR160-MdARF17-MdWRKY33 module is crucial for apple freezing tolerance. Mdm-miR160 plays a negative role in apple freezing tolerance, whereas MdARF17, one of the targets of Mdm-miR160, is a positive regulator of apple freezing tolerance. RNA sequencing analysis revealed that in apple, MdARF17 mediates the cold response by influencing the expression of cold-responsive genes. EMSA and ChIP-qPCR assays demonstrated that MdARF17 can bind to the promoter of MdWRKY33 and promotes its expression. Overexpression of MdWRKY33 enhanced the cold tolerance of the apple calli. In addition, we found that the Mdm-miR160-MdARF17-MdWRKY33 module regulates cold tolerance in apple by regulating reactive oxygen species (ROS) scavenging, as revealed by (i) increased H₂ O₂ levels and decreased peroxidase (POD) and catalase (CAT) activities in Mdm-miR160e OE plants and MdARF17 RNAi plants and (ii) decreased H₂ O₂ levels and increased POD and CAT activities in MdmARF17 OE plants and MdWRKY33 OE calli. Taken together, our study uncovered the molecular roles of the Mdm-miR160-MdARF17-MdWRKY33 module in freezing tolerance in apple, thus providing support for breeding of cold-tolerant apple cultivars.

Genome-wide annotation and expression analysis of WRKY and bHLH transcriptional factor families reveal their involvement under cadmium stress in tomato (Solanum lycopersicum L.)

The WRKY and bHLH transcription factors have been implicated in the regulation of gene expression during various physiological processes in plants, especially in plant stress responses. However, little information about the heavy metal-responsive SlWRKY and SlbHLH in tomato (Solanum lycopersicum) is available. We performed a genome-wide investigation for these two TF families in S. lycopersicum and determined their role in cadmium (Cd) stress tolerance. Furthermore, ortholog analysis with the Arabidopsis genome led to classifying WRKY and bHLH ortholog genes into nine and 11 clusters, respectively. The comparative phylogenetic analysis revealed duplication events and gene loss in Arabidopsis and S. lycopersicum, which occurred during evolution both before and after the last common ancestor of the two species. Orthologous relationships are also supported by additional evidence, such as gene structure, conserved motif compositions, and protein-protein interaction networks for the majority of genes, suggesting their similar functions. A comprehensive transcriptomics analysis revealed that both WRKY and bHLH genes were differentially expressed in response to cadmium stress as compared with control plants. A gene ontology analysis revealed that most WRKYs and bHLHs are DNA-binding essential proteins that regulate gene expression positively and negatively. Analyses of interaction networks revealed that both WRKYs and bHLHs mediate networks implicated in several stress-signaling pathways. The findings of this work may help us to comprehend the intricate transcriptional control of WRKY and bHLH genes and identify potential stress-responsive genes relevant to tomato genetic improvement. Moreover, identifying heavy metal stress-responsive WRKY and bHLH genes in S. lycopersicum will provide fundamental insights for developing new heavy metal stress-tolerant varieties of tomato crops.

Induction of Somatic Embryogenesis in Plants: Different Players and Focus on WUSCHEL and WUS-RELATED HOMEOBOX (WOX) Transcription Factors

In plants, other cells can express totipotency in addition to the zygote, thus resulting in embryo differentiation; this appears evident in apomictic and epiphyllous plants. According to Haberlandt's theory, all plant cells can regenerate a complete plant if the nucleus and the membrane system are intact. In fact, under in vitro conditions, ectopic embryos and adventitious shoots can develop from many organs of the mature plant body. We are beginning to understand how determination processes are regulated and how cell specialization occurs. However, we still need to unravel the mechanisms whereby a cell interprets its position, decides its fate, and communicates it to others. The induction of somatic embryogenesis might be based on a plant growth regulator signal (auxin) to determine an appropriate cellular environment and other factors, including stress and ectopic expression of embryo or meristem identity transcription factors (TFs). Still, we are far from having a complete view of the regulatory genes, their target genes, and their action hierarchy. As in animals, epigenetic reprogramming also plays an essential role in re-establishing the competence of differentiated cells to undergo somatic embryogenesis. Herein, we describe the functions of WUSCHEL-RELATED HOMEOBOX (WOX) transcription factors in regulating the differentiation-dedifferentiation cell process and in the developmental phase of in vitro regenerated adventitious structures.

Characterization of WOX genes revealed drought tolerance, callus induction, and tissue regeneration in Gossypium hirsutum

Cotton is an important natural fiber crop; its seeds are the main oil source. Abiotic stresses cause a significant decline in its production. The WUSCHEL-related Homeobox (WOX) genes have been involved in plant growth, development, and stress responses. However, the functions of WOX genes are less known in cotton. This study identified 39, 40, 21, and 20 WOX genes in Gossypium hirsutum, Gossypium barbadense, Gossypium arboreum, and Gossypium raimondii, respectively. All the WOX genes in four cotton species could be classified into three clades, which is consistent with previous research. The gene structure and conserved domain of all WOX genes were analyzed. The expressions of WOX genes in germinating hypocotyls and callus were characterized, and it was found that most genes were up-regulated. One candidate gene Gh_ A01G127500 was selected to perform the virus-induced gene silencing (VIGS) experiment, and it was found that the growth of the silenced plant (pCLCrVA: GhWOX4_A01) was significantly inhibited compared with the wild type. In the silenced plant, there is an increase in antioxidant activities and a decrease in oxidant activities compared with the control plant. In physiological analysis, the relative electrolyte leakage level and the excised leaf water loss of the infected plant were increased. Still, both the relative leaf water content and the chlorophyll content were decreased. This study proved that WOX genes play important roles in drought stress and callus induction, but more work must be performed to address the molecular functions of WOX genes.

In silico genome wide identification and expression analysis of the WUSCHEL-related homeobox gene family in Medicago sativa

Alfalfa (Medicago sativa) is an important food and feed crop which rich in mineral sources. The WUSCHEL-related homeobox (WOX) gene family plays important roles in plant development and identification of putative gene families, their structure, and potential functions is a primary step for not only understanding the genetic mechanisms behind various biological process but also for genetic improvement. A variety of computational tools, including MAFFT, HMMER, hidden Markov models, Pfam, SMART, MEGA, ProtTest, BLASTn, and BRAD, among others, were used. We identified 34 MsWOX genes based on a systematic analysis of the alfalfa plant genome spread in eight chromosomes. This is an expansion of the gene family which we attribute to observed chromosomal duplications. Sequence alignment analysis revealed 61 conserved proteins containing a homeodomain. Phylogenetic study sung reveal five evolutionary clades with 15 motif distributions. Gene structure analysis reveals various exon, intron, and untranslated structures which are consistent in genes from similar clades. Functional analysis prediction of promoter regions reveals various transcription binding sites containing key growth, development, and stress-responsive transcription factor families such as MYB, ERF, AP2, and NAC which are spread across the genes. Most of the genes are predicted to be in the nucleus. Also, there are duplication events in some genes which explain the expansion of the family. The present research provides a clue on the potential roles of MsWOX family genes that will be useful for further understanding their functional roles in alfalfa plants.

Enhancement of plant cold tolerance by soybean RCC1 family gene GmTCF1a

BACKGROUND

Low temperature severely limits the growth, yield, and geographic distributions of soybean. Soybean plants respond to cold stress by reprogramming the expression of a series of cold-responsive genes. However, the intrinsic mechanism underlying cold-stress tolerance in soybean remains unclear. A. thaliana tolerant to chilling and freezing 1 (AtTCF1) is a regulator of chromosome condensation 1 (RCC1) family protein and regulates freezing tolerance through an independent C-repeat binding transcription factor (CBF) signaling pathway.

RESULTS

In this study, we identified a homologous gene of AtTCF1 in soybean (named GmTCF1a), which mediates plant tolerance to low temperature. Like AtTCF1, GmTCF1a contains five RCC1 domains and is located in the nucleus. GmTCF1a is strongly and specifically induced by cold stress. Interestingly, ectopic overexpression of GmTCF1a in Arabidopsis greatly increased plant survival rate and decreased electrolyte leakage under freezing stress. A cold-responsive gene, COR15a, was highly induced in the GmTCF1a-overexpressing transgenic lines.

CONCLUSIONS

GmTCF1a responded specifically to cold stress, and ectopic expression of GmTCF1a enhanced cold tolerance and upregulated COR15a levels. These results indicate that GmTCF1a positively regulates cold tolerance in soybean and may provide novel insights into genetic improvement of cold tolerance in crops.

Elevation of GhDREB1B transcription by a copy number variant significantly improves chilling tolerance in cotton

The elevation of transcript levels of GhDREB1B causes the accumulation of osmoregulants and mitigation of reactive oxygen species, which contributes to the enhanced resistance to chilling stress in AiSheng98 cotton. Low temperature is one of the key environmental stresses that impairs cotton growth and restricts fiber productivity. Dehydration responsive element binding (DREB) transcription factors play an important role in cold response in plants by modulating the transcription level of cold-responsive genes to protect the plants from low-temperature stress. Here, we showed that GhDREB1B, a copy number variant in the AiSheng98 (AS98) cotton mutant, significantly improved chilling tolerance in cotton seedlings, while silencing of GhDREB1B made transgenic cotton sensitive to chilling stress in AS98 cotton compared with control plants. Elevated GhDREB1B transcript level activated the expression of major cold-responsive genes. Genome-wide expression profiling by RNA sequencing revealed the upregulation of genes related to fatty acids, lipid proteins, osmoprotection, and anti-oxidative enzymes in AiSheng98. Excessive accumulation of malondialdehyde (MDA) and higher ion leakage rates occurred in wild-type LFH10 plants when compared to those of Aisheng98 during chilling stress, signifying lower chilling tolerance in the wild-type than in Aisheng98. Furthermore, the Aisheng98 mutant under chilling stress accumulated higher levels of free proline and soluble sugar than LFH10 accumulated. These results suggest that GhDREB1B is a positive regulator and its variant can alter the expression patterns of major low-temperature stress-related genes and enhance chilling tolerance in cotton.

Proteomics of Homeobox7 Enhanced Salt Tolerance in Mesembryanthemum crystallinum

Mesembryanthemum crystallinum (common ice plant) is a halophyte species that has adapted to extreme conditions. In this study, we cloned a McHB7 transcription factor gene from the ice plant. The expression of McHB7 was significantly induced by 500 mM NaCl and it reached the peak under salt treatment for 7 days. The McHB7 protein was targeted to the nucleus. McHB7-overexpressing in ice plant leaves through Agrobacterium-mediated transformation led to 25 times more McHB7 transcripts than the non-transformed wild type (WT). After 500 mM NaCl treatment for 7 days, the activities of superoxide dismutase (SOD) and peroxidase (POD) and water content of the transgenic plants were higher than the WT, while malondialdehyde (MDA) was decreased in the transgenic plants. A total of 1082 and 1072 proteins were profiled by proteomics under control and salt treatment, respectively, with 22 and 11 proteins uniquely identified under control and salt stress, respectively. Among the 11 proteins, 7 were increased and 4 were decreased after salt treatment. Most of the proteins whose expression increased in the McHB7 overexpression (OE) ice plants under high salinity were involved in transport regulation, catalytic activities, biosynthesis of secondary metabolites, and response to stimulus. The results demonstrate that the McHB7 transcription factor plays a positive role in improving plant salt tolerance.

Overexpression of the V-ATPase c subunit gene from Antarctic notothenioid fishes enhances freezing tolerance in transgenic Arabidopsis plants

Theoretical and experimental studies have demonstrated that temperature is an important environmental factor that affects the regional distribution of plants. However, how to modify the distribution pattern of plants in different regions is a focus of current research. Obtain the information of cold tolerance genes from cold tolerance species, cloning genes with real cold tolerance effects is one of the most important ways to find the genes related to cold tolerance. In this study, we investigated whether transferring the VHA-c gene from Antarctic notothenioid fishes into Arabidopsis enhances freezing tolerance of Arabidopsis. The physiological response and molecular changes of VHA-c overexpressing pedigree and wildtype Arabidopsis were studied at -20 °C. The results showed that the malondialdehyde (MDA) and membrane leakage rates of WT plants were significantly higher than those of VHA-c8 and VHA-c11 plants, but the soluble sugar, soluble protein, proline and ATP contents of WT plants were significantly lower than those of VHA-c8 and VHA-c11 plants under -20 °C freezing treatment. The survival rate, VHA-c gene expression level and VHA-c protein contents of WT plants were significantly lower than those of VHA-c8 and VHA-c11 plants under -20 °C freezing treatment. Correlation analysis showed that ATP content was significantly negatively correlated with MDA and membrane leakage rate, and positively correlated with soluble sugar, soluble protein and proline content under -20 °C freezing treatment. These results demonstrated that overexpression of the VHA-c gene provided strong freezing tolerance to Arabidopsis by increasing the synthesis of ATP and improved the adaptability of plants in low temperature environment.

Genome-wide identification and characterization of WOX genes in Cucumis sativus

WUSCHEL-related homeobox (WOX) proteins are plant-specific transcription factors that are profoundly involved in regulation of plant development and stress responses. In this study, we totally identified 11 WOX transcription factor family members in cucumber (Cucumis sativus, CsWOX) genome and classified them into three clades with nine subclades based on phylogenetic analysis results. Alignment of amino acid sequences revealed that all WOX members in cucumber contained the typical homeodomain, which consists of 60-66 amino acids and is folded into a helix-turn-helix structure. Gene duplication event analysis indicated that CsWOX1a and CsWOX1b were a segment duplication pair, which might affect the number of WOX members in cucumber genome. The expression profiles of CsWOX genes in different tissues demonstrated that the members sorted into the ancient clade (CsWOX13a and CsWOX13b) were constitutively expressed at higher levels in comparison to the others. Cis-element analysis in promoter regions suggested that the expression of CsWOX genes was associated with phytohormone pathways and stress responses, which was further supported by RNA-seq data. Taken together, our results provide new insights into the evolution of cucumber WOX genes and improve our understanding about the biological functions of the CsWOX gene family.

Functional Validation of Glutamine synthetase and Glutamate synthase Genes in Durum Wheat near Isogenic Lines with QTL for High GPC

Durum wheat (Triticum turgidum L. ssp. durum) is a minor crop grown on about 17 million hectares of land worldwide. Several grain characteristics determine semolina's high end-use quality, such as grain protein content (GPC) which is directly related to the final products' nutritional and technological values. GPC improvement could be pursued by considering a candidate gene approach. The glutamine synthetase (GS)/glutamate synthase (GOGAT) cycle represents a bottleneck in the first step of nitrogen assimilation. QTL for GPC have been located on all chromosomes, and several major ones have been reported on 2A and 2B chromosomes, where GS2 and Fd-GOGAT genes have been mapped. A useful and efficient method to validate a putative QTL is the constitution of near-isogenic lines (NILs) by using the marker found to be associated to that QTL. Here, we present the development of two distinct sets of heterogeneous inbred family (HIF)- based NILs segregating for GS2 and Fd-GOGAT genes obtained from heterozygous lines at those loci, as well as their genotypic and phenotypic characterizations. The results allow the validation of the previously identified GPC QTL on 2A and 2B chromosomes, along with the role of these key genes in GPC control.

SlMYB102 expression enhances low-temperature stress resistance in tomato plants

Herein, we identified the tomato SlMYB102 gene as a MYB family transcription factor of the R2R3-MYB subfamily. We additionally determined that the SlMYB102 promoter region contains photoresponsive, abiotic stress-responsive, and hormone-responsive regulatory elements, and we detected higher SlMYB102 expression in the reproductive organs of tomato than that in vegetative organs, with the expression being highest in ripe fruits and in roots. SlMYB102 expression was also shown to be cold-inducible. The protein encoded by SlMYB102 localized to the nucleus wherein it was found to mediate the transcriptional activation of target genes through its C-terminal domain. Overexpression of SlMYB102 in tomato plants conferred enhanced tolerance to cold stress. Under such cold stress conditions, we found that proline levels in the leaves of SlMYB102 overexpressing transgenic plants were higher than those in WT plants. In addition, S1MYB102 overexpression was associated with the enhanced expression of cold response genes including SlCBF1, SlCBF3, SlDREB1, SlDEB2, and SlICE1. We also found that the overexpression of SlMYB102 further enhanced the cold-induced upregulation of SlP5CS and SlAPX2. Taken together, these results suggest that SlMYB102 may be involved in the C-repeat binding transcription factor (CBF) and proline synthesis pathways, thereby improving tomato plant cold resistance.

SlMYB102 expression enhances low-temperature stress resistance in tomato plants

Herein, we identified the tomato SlMYB102 gene as a MYB family transcription factor of the R2R3-MYB subfamily. We additionally determined that the SlMYB102 promoter region contains photoresponsive, abiotic stress-responsive, and hormone-responsive regulatory elements, and we detected higher SlMYB102 expression in the reproductive organs of tomato than that in vegetative organs, with the expression being highest in ripe fruits and in roots. SlMYB102 expression was also shown to be cold-inducible. The protein encoded by SlMYB102 localized to the nucleus wherein it was found to mediate the transcriptional activation of target genes through its C-terminal domain. Overexpression of SlMYB102 in tomato plants conferred enhanced tolerance to cold stress. Under such cold stress conditions, we found that proline levels in the leaves of SlMYB102 overexpressing transgenic plants were higher than those in WT plants. In addition, S1MYB102 overexpression was associated with the enhanced expression of cold response genes including SlCBF1, SlCBF3, SlDREB1, SlDEB2, and SlICE1. We also found that the overexpression of SlMYB102 further enhanced the cold-induced upregulation of SlP5CS and SlAPX2. Taken together, these results suggest that SlMYB102 may be involved in the C-repeat binding transcription factor (CBF) and proline synthesis pathways, thereby improving tomato plant cold resistance.

Understanding the early cold response mechanism in IR64 indica rice variety through comparative transcriptome analysis

Background

Cellular reprogramming in response to environmental stress involves alteration of gene expression, changes in the protein and metabolite profile for ensuring better stress management in plants. Similar to other plant species originating in tropical and sub-tropical areas, indica rice is highly sensitive to low temperature that adversely affects its growth and grain productivity. Substantial work has been done to understand cold induced changes in gene expression in rice plants. However, adequate information is not available for early gene expression, especially in indica variety. Therefore, a transcriptome profile was generated for cold shock treated seedlings of IR64 variety to identify early responsive genes.

Results

The functional annotation of early DEGs shows enrichment of genes involved in altered membrane rigidity and electrolytic leakage, the onset of calcium signaling, ROS generation and activation of stress responsive transcription factors in IR64. Gene regulatory network suggests that cold shock induced Ca2+ signaling activates DREB/CBF pathway and other groups of transcription factors such as MYB, NAC and ZFP; for activating various cold-responsive genes. The analysis also indicates that cold induced signaling proteins like RLKs, RLCKs, CDPKs and MAPKK and ROS signaling proteins. Further, several late-embryogenesis-abundant (LEA), dehydrins and low temperature-induced-genes were upregulated under early cold shock condition, indicating the onset of water-deficit conditions. Expression profiling in different high yielding cultivars shows high expression of cold-responsive genes in Heera and CB1 indica varieties. These varieties show low levels of cold induced ROS production, electrolytic leakage and high germination rate post-cold stress, compared to IR36 and IR64. Collectively, these results suggest that these varieties may have improved adaptability to cold stress.

Conclusions

The results of this study provide insights about early responsive events in Oryza sativa l.ssp. indica cv IR64 in response to cold stress. Our data shows the onset of cold response is associated with upregulation of stress responsive TFs, hydrophilic proteins and signaling molecules, whereas, the genes coding for cellular biosynthetic enzymes, cell cycle control and growth-related TFs are downregulated. This study reports that the generation of ROS is integral to the early response to trigger the ROS mediated signaling events during later stages.

Genome-Wide Identification of the Physic Nut WUSCHEL-Related Homeobox Gene Family and Functional Analysis of the Abiotic Stress Responsive Gene JcWOX5

Plant-specific WOX transcription factors have important regulatory functions in plant development and response to abiotic stress. However, the identification and functional analysis of members of the WOX family have rarely been reported in the physic nut plant until now. Our research identified 12 WOX genes (JcWOXs) in physic nut, and these genes were divided into three groups corresponding to the ancient clade, WUS clade, and intermediate clade. Expression analysis based on RNA-seq and qRT-PCR showed that most of the JcWOX genes were expressed in at least one of the tissues tested, whereas five genes were identified as being highly responsive to drought and salt stresses. Subcellular localization analysis in Arabidopsis protoplast cells showed that JcWOX5 encoded a nuclear-localized protein. JcWOX5-overexpression plants increased sensitivity to drought stress, and transgenic plants suggested a lower proline content and CAT activity, higher relative electrolyte leakage, higher MDA content, and higher rate of water loss under drought conditions. Expression of some stress-related genes was obviously lower in the transformed rice lines as compared to their expression in wild-type rice lines under drought stress. Further data on JcWOX5-overexpressing plants reducing drought tolerance verified the potential role of JcWOX genes in responsive to abiotic stress. Collectively, the study provides a foundation for further functional analysis of JcWOX genes and the improvement of physic nut crops.

Molecular genetic analyses of abiotic stress responses during plant reproductive development

Plant responses to abiotic stresses during vegetative growth have been extensively studied for many years. Daily environmental fluctuations can have dramatic effects on plant vegetative growth at multiple levels, resulting in molecular, cellular, physiological, and morphological changes. Plants are even more sensitive to environmental changes during reproductive stages. However, much less is known about how plants respond to abiotic stresses during reproduction. Fortunately, recent advances in this field have begun to provide clues about these important processes, which promise further understanding and a potential contribution to maximize crop yield under adverse environments. Here we summarize information from several plants, focusing on the possible mechanisms that plants use to cope with different types of abiotic stresses during reproductive development, and present a tentative molecular portrait of plant acclimation during reproductive stages. Additionally, we discuss strategies that plants use to balance between survival and productivity, with some comparison among different plants that have adapted to distinct environments.

Salinity tolerance in barley during germination- homologs and potential genes

Salinity affects more than 6% of the world's total land area, causing massive losses in crop yield. Salinity inhibits plant growth and development through osmotic and ionic stresses; however, some plants exhibit adaptations through osmotic regulation, exclusion, and translocation of accumulated Na+ or Cl-. Currently, there are no practical, economically viable methods for managing salinity, so the best practice is to grow crops with improved tolerance. Germination is the stage in a plant's life cycle most adversely affected by salinity. Barley, the fourth most important cereal crop in the world, has outstanding salinity tolerance, relative to other cereal crops. Here, we review the genetics of salinity tolerance in barley during germination by summarizing reported quantitative trait loci (QTLs) and functional genes. The homologs of candidate genes for salinity tolerance in Arabidopsis, soybean, maize, wheat, and rice have been blasted and mapped on the barley reference genome. The genetic diversity of three reported functional gene families for salt tolerance during barley germination, namely dehydration-responsive element-binding (DREB) protein, somatic embryogenesis receptor-like kinase and aquaporin genes, is discussed. While all three gene families show great diversity in most plant species, the DREB gene family is more diverse in barley than in wheat and rice. Further to this review, a convenient method for screening for salinity tolerance at germination is needed, and the mechanisms of action of the genes involved in salt tolerance need to be identified, validated, and transferred to commercial cultivars for field production in saline soil.

An apple MYB transcription factor regulates cold tolerance and anthocyanin accumulation and undergoes MIEL1-mediated degradation

MYB transcription factors (TFs) have been demonstrated to play diverse roles in plant growth and development through interaction with basic helix-loop-helix (bHLH) TFs. MdbHLH33, an apple bHLH TF, has been identified as a positive regulator in cold tolerance and anthocyanin accumulation by activating the expressions of MdCBF2 and MdDFR. In the present study, a MYB TF MdMYB308L was found to also positively regulate cold tolerance and anthocyanin accumulation in apple. We found that MdMYB308L interacted with MdbHLH33 and enhanced its binding to the promoters of MdCBF2 and MdDFR. In addition, an apple RING E3 ubiquitin ligase MYB30-INTERACTING E3 LIGASE 1 (MdMIEL1) was identified to be an MdMYB308L-interacting protein and promoted the ubiquitination degradation of MdMYB308L, thus negatively regulated cold tolerance and anthocyanin accumulation in apple. These results suggest that MdMYB308L acts as a positive regulator in cold tolerance and anthocyanin accumulation in apple by interacting with MdbHLH33 and undergoes MdMIEL1-mediated protein degradation. The dynamic change in MYB-bHLH protein complex seems to play a key role in the regulation of plant growth and development.

Large-scale phylogenomic analysis suggests three ancient superclades of the WUSCHEL-RELATED HOMEOBOX transcription factor family in plants

The adaptation of plants to land required multiple morphological innovations. Among these include a variety of lateral organs that are initiated from apical meristems, in which the mantainance of undifferentiated stem cells is regulated by the homeodomain WUSCHEL-RELATED (WOX) transcription factors. Expansion of the WOX gene family has been associated with whole genome duplication (WGD) events and postulated to have been pivotal to the evolution of morphological complexity in land plants. Previous studies have classified the WOX gene family into three superclades (e.g., the ancient clade, the intermediate clade, and the modern clade). In order to improve our understanding of the evolution of the WOX gene family, we surveyed the WOX gene sequences from 38 genomes and 440 transcriptomes spanning the Viridiplantae and Rhodophyta. The WOX phylogeny inferred from 1039 WOX proteins drawn from 267 species with improved support along the backbone of the phylogeny suggests that the plant-specific WOX family contains three ancient superclades, which we term Type 1 (T1WOX, the WOX10/13/14 clade), Type 2 (T2WOX, the WOX8/9 and WOX11/12 clades), and Type 3 (T3WOX, the WUS, WOX1/6, WOX2, WOX3, WOX4 and WOX5/7 clades). Divergence of the T1WOX and T2WOX superclades may predate the diversification of vascular plants. Synteny analysis suggests contribution of WGD to expansion of the WOX family. Promoter analysis finds that the capacity of the WOX genes to be regulated by the auxin and cytokinin signaling pathways may be deeply conserved in the Viridiplantae. This study improves our phylogenetic context for elucidating functional evolution of the WOX gene family, which has likely contributed to the morphological complexity of land plants.

Analysis of differential gene expression in cold-tolerant vs. cold-sensitive varieties of snap bean (Phaseolus vulgaris L.) in response to low temperature stress

BACKGROUND

Snap bean, Phaseolus vulgaris L., as a warm-season vegetable, low temperature stress seriously affect the yield and quality. At present, little is known about the genes and molecular regulation mechanism in cold response in snap bean exposed to low temperature.

OBJECTIVES

Our objectives were to identify the low temperature response genes in snap bean and to examine differences in the gene response between cold-tolerant and cold-sensitive genotypes.

METHODS

We used two highly inbred snap bean lines in this study, the cold-tolerant line '120', and the cold-sensitive line '093'. The plants were grown to the three leaf and one heart stage and exposed to 4 °C low temperature. We used RNA sequencing (RNA-seq) to analyze the differences of gene expression.

RESULTS

988 and 874 cold-responsive genes were identified in 'T120 vs CK120' and 'T093 vs CK093' ('T' stands for low temperature treatment, and 'CK' stands for control at room temperature), respectively. Of these, 555 and 442 genes were unique to cold-stressed lines '120' and '093', respectively compared to the control. Our analysis of these differentially expressed genes indicates that Ca²⁺, ROS, and hormones act as signaling molecules that play important roles in low temperature response in P. vulgaris. Altering the expression of genes in these signaling pathways activates expression of downstream response genes which can interact with other signaling regulatory networks. This may maintained the balance of ROS and hormones, making line '120' more cold-tolerant than line '093'.

CONCLUSION

Our results provide a preliminarily understanding of the molecular basis of low temperature response in snap bean, and also establish a foundation for the future genetic improvement of cold sensitivity in snap bean by incorporating genes for cold tolerance.

Genome-Wide Analysis of the WOX Gene Family and Function Exploration of GmWOX18 in Soybean

WUSCHEL-related homeobox (WOX) is a family of transcription factors that are unique to plants and is characterized by the presence of a homeodomain. The WOX transcription factor plays an important role in regulating plant growth and development and the response to abiotic stress. Soybean is one of the most important oil crops worldwide. In this study, based on the available genome data of soybean, the WOX gene family was identified by bioinformatics analysis. The chromosome distribution, gene and protein structures, phylogenetic relationship and gene expression patterns of this family were comprehensively compared. The results showed that a total of 33 putative WOX genes in the soybean genome were found and then designated as GmWOX1- GmWOX33, which were distributed across 19 chromosomes except chromosome 16. Multiple sequence analysis of the GmWOX gene family revealed a highly conserved homeodomain. Phylogenetic tree analysis showed that 33 WOX genes could be divided into three major clades (modern/WUS, intermediate and ancient) in soybean. Of these 33 WOX genes, some showed differential expression patterns in the tested tissues (leaves, pods, unopen and open flowers, nodules, seed, roots, root hairs, stems, shoot apical meristems and shoot tips). In addition, the expression profile and qRT-PCR analysis showed that most of the GmWOX genes responded to different abiotic stress treatments (cold and drought). According to the expression pattern of GmWOX genes in the high regeneration capacity soybean material P3, overexpression of GmWOX18 was selected for function analysis. The overexpression of GmWOX18 increased the regeneration ability of clustered buds. The results will provide valuable information for further studies on the roles of WOX genes in regulating soybean growth, development and responses to abiotic stress, as well as a basis for the functional identification and analysis of WOX genes in soybean.

ERF109 of trifoliate orange (Poncirus trifoliata (L.) Raf.) contributes to cold tolerance by directly regulating expression of Prx1 involved in antioxidative process

Ethylene-responsive factors (ERFs) have been revealed to play essential roles in a variety of physiological and biological processes in higher plants. However, functions and regulatory pathways of most ERFs in cold stress remain largely unclear. Here, we identified PtrERF109 of trifoliate orange (Poncirus trifoliata (L.) Raf.) and deciphered its role in cold tolerance. PtrERF109 was drastically up-regulated by cold, ethylene and dehydration, but repressed by salt. PtrERF109 was localized in the nucleus and displayed transcriptional activity, and the C terminus is required for the activation. Overexpression of PtrERF109 conferred enhanced cold tolerance in transgenic tobacco and lemon plants, whereas VIGS (virus-induced gene silencing)-mediated suppression of PtrERF109 in trifoliate orange led to increased cold susceptibility. PtrERF109 overexpression caused extensive transcriptional reprogramming of several suites of stress-responsive genes. Prx1 encoding class III peroxidase (POD) was one of the antioxidant genes exhibiting the greatest induction. PtrERF109 was shown to directly bind to the promoter of PtrPrx1 (trifoliate orange Prx1 homologue) and positively activated its expression. In addition, the PtrERF109-overexpressing plants exhibited significantly higher POD activity and accumulated dramatically less H₂ O₂ and were more tolerant to oxidative stress, whereas the VIGS plants exhibited opposite trends, in comparison with wild type. Taken together, these results indicate that PtrERF109 as a positive regulator contributes to imparting cold tolerance by, at least partly, directly regulating the POD-encoding gene to maintain a robust antioxidant capacity for effectively scavenging the reactive oxygen species. Our findings gain insight into better understanding of transcriptional regulation of antioxidant genes in response to cold stress.

Genes associated with chloroplasts and hormone-signaling, and transcription factors other than CBFs are associated with differential survival after low temperature treatments of Camelina sativa biotypes

Winter annual biotypes of Camelina sativa regularly survive after winter conditions experienced in northern regions of the U.S., whereas summer annual biotypes do not. To determine potential molecular mechanisms associated with these biotype differences in survival after low temperature treatments, we examined genetic and transcript variations in both a winter- (Joelle) and a summer- (CO46) biotype. It was determined that as few as one or two dominant genes may control differential survival after low temperature treatments. Of the 1797 genes that were differentially expressed in response to cold in both the winter and summer biotypes many COR genes were identified, indicating that the CBF regulon is functional in both. However, only 153 and 76 genes from Joelle and CO46, respectively, were either differentially expressed or not expressed at all in one biotype versus the other following cold acclimation. We hypothesize that these 229 genes play a significant role in, or are primarily responsive to, differences in survival after freezing between these two biotypes. Promoter analysis provided few clues as to the regulation or these genes; however, genes that were down-regulated specifically in the winter biotype Joelle were enriched with the sequence TGGCCCTCGCTCAC, which is over-represented among genes associated with chloroplasts in Arabidopsis. Additionally, several genes involved in auxin signaling were down-regulated specifically in Joelle. A transcription factor with strong similarity to MYB47, known to be up-regulated by salt, drought, and jasmonic acid, but not cold in Arabidopsis, was essentially off in the freezing sensitive biotype CO46, but was cold-induced in the winter biotype Joelle. Several other transcription factors genes including three with similarity to WRKY70, that may be involved in SA/JA-dependent responses, a HOMEOBOX 6 gene involved in ABA signaling, and two others (NUCLEAR FACTOR Y and CONSTANS-like 2) known to be implicated in photoperiodic flowering were also differentially expressed between the two biotypes.

Crop Improvement Through Temperature Resilience

Abnormal environmental temperature affects plant growth and threatens crop production. Understanding temperature signal sensing and the balance between defense and development in plants lays the foundation for improvement of temperature resilience. Here, we summarize the current understanding of cold signal perception/transduction as well as heat stress response. Dissection of plant responses to different levels of cold stresses (chilling and freezing) illustrates their common and distinct signaling pathways. Axillary bud differentiation in response to chilling is presented as an example of the trade-off between defense and development. Vernalization is a cold-dependent development adjustment mediated by O-GlcNAcylation and phosphorylation to sense long-term cold. Recent progress on major quantitative trait loci genes for heat tolerance has been summarized. Molecular mechanisms in utilizing temperature-sensitive sterility in super hybrid breeding in China are revealed. The way to improve crop temperature resilience using integrative knowledge of omics as well as systemic and synthetic biology, especially the molecular module program, is summarized.

BYPASS1-LIKE, A DUF793 Family Protein, Participates in Freezing Tolerance via the CBF Pathway in Arabidopsis

The C-REPEAT BINDING FACTOR signaling pathway is strictly modulated by numerous factors and is essential in the cold response of plants. Here, we show that the DUF793 family gene BYPASS1-LIKE modulates freezing tolerance through the CBFs in Arabidopsis. The expression of B1L was rapidly induced under cold treatment. Comparing to wild type, B1L knockout mutants were more sensitive to freezing treatment, whereas B1L-overexpressing lines were more tolerant. The expression of CBFs and CBF target genes was significantly decreased in b1l mutant. Using yeast two-hybrid screening system, 14-3-3λ was identified as one of proteins interacting with B1L. The interaction was confirmed with bimolecular fluorescence complementation assay and co-immunoprecipitation assay. Biochemical assays revealed that b1l mutation promoted the degradation of CBF3 compared to wild type, whereas 14-3-3κλ mutant and b1l 14-3-3κλ mutant suppressed the degradation of CBF3. Consistently, 14-3-3κλ and b1l 14-3-3κλ mutants showed enhanced freezing tolerance compared to wild type. These results indicate that B1L enhances the freezing tolerance of plants, at least partly through stabilizing CBF. Our findings improve our understanding of the regulation of CBF in response to cold stress.

R2R3-MYB transcription factor MdMYB23 is involved in the cold tolerance and proanthocyanidin accumulation in apple

Cold stress severely affects plant growth and yield. C-repeat binding factors (CBFs) play important roles in the response to cold stress. In the present study, we identified an R2R3-MYB transcription factor (TF) MdMYB23 from apple (Malus × domestic) using transcriptome analyses, which was notably induced in response to cold stress. Transgenic apple calli and Arabidopsis with overexpression of MdMYB23 exhibited increased cold tolerance. Electrophoretic mobility shift assay (EMSA) and transient expression assays indicated that MdMYB23 directly bound to the promoters of MdCBF1 and MdCBF2 and activated their expression. MdMYB23 interacted with the promoter of MdANR, a key modulator of proanthocyanidin biosynthesis, and activated its expression to promote proanthocyanidin accumulation and reactive oxygen species (ROS) scavenging. MdBT2 was identified as an MdMYB23-interacting protein using yeast two-hybrid (Y2H), pull-down, and bimolecular fluorescence complementation (BiFC) assays. MdBT2 repressed cold tolerance and proanthocyanidin accumulation by promoting the degradation of MdMYB23 protein. Our findings shed light on the functions of MYB TFs and underlying mechanism in the modulation of plant cold tolerance.

Insights into the regulation of C-repeat binding factors in plant cold signaling

Cold temperatures, a major abiotic stress, threaten the growth and development of plants, worldwide. To cope with this adverse environmental cue, plants from temperate climates have evolved an array of sophisticated mechanisms to acclimate to cold periods, increasing their ability to tolerate freezing stress. Over the last decade, significant progress has been made in determining the molecular mechanisms underpinning cold acclimation, including following the identification of several pivotal components, including candidates for cold sensors, protein kinases, and transcription factors. With these developments, we have a better understanding of the CBF-dependent cold-signaling pathway. In this review, we summarize recent progress made in elucidating the cold-signaling pathways, especially the C-repeat binding factor-dependent pathway, and describe the regulatory function of the crucial components of plant cold signaling. We also discuss the unsolved questions that should be the focus of future work.

Enhancing freezing tolerance of Brassica napus L. by overexpression of a stearoyl-acyl carrier protein desaturase gene (SAD) from Sapium sebiferum (L.) Roxb

Sapium sebiferum (L.) Roxb. is an important woody oil tree and traditional herbal medicine in China. Stearoyl-acyl carrier protein desaturase (SAD) is a dehydrogenase enzyme that plays a key role in the transformation of saturated fatty acids into unsaturated fatty acids in oil; these fatty acids greatly influence the freezing tolerance of plants. However, it remains unclear whether freezing tolerance can be regulated by the expression level of SsSAD in S. sebiferum L. Our research indicated that SsSAD expression in S. sebiferum L. increased under freezing stress. To further confirm this result, we constructed a pEGAD-SsSAD vector and transformed it into B. napus L. W10 by Agrobacterium tumefaciens-mediated transformation. Transgenic plants that overexpressed the SsSAD gene exhibited significantly higher linoleic (18:2) and linolenic acid (18:3) content and advanced freezing tolerance. These results suggest that SsSAD overexpression in B. napus L. can increase the content of polyunsaturated fatty acids (PUFAs) such as linoleic (18:2) and linolenic acid (18:3), which are likely pivotal in improving freezing tolerance in B. napus L. plants. Thus, SsSAD overexpression could be useful in the production of freeze-tolerant varieties of B. napus L.

An atypical R2R3 MYB transcription factor increases cold hardiness by CBF-dependent and CBF-independent pathways in apple

Apple (Malus × domestica) trees are vulnerable to freezing temperatures. However, there has been only limited success in developing cold-hardy cultivars. This lack of progress is due at least partly to lack of understanding of the molecular mechanisms of freezing tolerance in apple. In this study, we evaluated the potential roles for two R2R3 MYB transcription factors (TFs), MYB88 and the paralogous FLP (MYB124), in cold stress in apple and Arabidopsis. We found that MYB88 and MYB124 positively regulate freezing tolerance and cold-responsive gene expression in both apple and Arabidopsis. Chromatin-Immunoprecipitation-qPCR and electrophoretic mobility shift assays showed that MdMYB88/MdMYB124 act as direct regulators of the COLD SHOCK DOMAIN PROTEIN 3 (MdCSP3) and CIRCADIAN CLOCK ASSOCIATED 1 (MdCCA1) genes. Dual luciferase reporter assay indicated that MdCCA1 but not MdCSP3 activated the expression of MdCBF3 under cold stress. Moreover, MdMYB88 and MdMYB124 promoted anthocyanin accumulation and H₂ O₂ detoxification in response to cold. Taken together, our results suggest that MdMYB88 and MdMYB124 positively regulate cold hardiness and cold-responsive gene expression under cold stress by C-REPEAT BINDING FACTOR (CBF)-dependent and CBF-independent pathways.

The GARP/MYB-related grape transcription factor AQUILO improves cold tolerance and promotes the accumulation of raffinose family oligosaccharides

Grapevine (Vitis vinifera L.) is a widely cultivated fruit crop whose growth and productivity are greatly affected by low temperatures. On the other hand, wild Vitis species represent valuable genetic resources of natural stress tolerance. We have isolated and characterized a MYB-like gene encoding a putative GARP-type transcription factor from Amur grape (V. amurensis) designated as VaAQUILO. AQUILO (AQ) is induced by cold in both V. amurensis and V. vinifera, and its overexpression results in significantly improved tolerance to cold both in transgenic Arabidopsis and in Amur grape calli. In Arabidopsis, the ectopic expression of VaAQ increased antioxidant enzyme activities and up-regulated reactive oxygen species- (ROS) scavenging-related genes. Comparative mRNA sequencing profiling of 35S:VaAQ Arabidopsis plants suggests that this transcription factor is related to phosphate homeostasis like their Arabidopsis closest homologues: AtHRS1 and AtHHO2. However, when a cold stress is imposed, AQ is tightly associated with the cold-responsive pathway and with the raffinose family oligosaccharides (RFOs), as observed by the up-regulation of galactinol synthase (GoLS) and raffinose synthase genes. Gene co-expression network (GCN) and cis-regulatory element (CRE) analyses in grapevine indicated AQ as potentially regulating VvGoLS genes. Increased RFO content was confirmed in both transgenic Arabidopsis and Amur grape calli overexpressing VaAQ. Taken together, our results imply that AQ improves cold tolerance through promoting the accumulation of osmoprotectants.

Transcriptomic Insights into Phenological Development and Cold Tolerance of Wheat Grown in the Field

Cold acclimation and winter survival in cereal species is determined by complicated environmentally regulated gene expression. However, studies investigating these complex cold responses are mostly conducted in controlled environments that only consider the responses to single environmental variables. In this study, we have comprehensively profiled global transcriptional responses in crowns of field-grown spring and winter wheat (Triticum aestivum) genotypes and their near-isogenic lines with the VRN-A1 alleles swapped. This in-depth analysis revealed multiple signaling, interactive pathways that influence cold tolerance and phenological development to optimize plant growth and development in preparation for a wide range of over-winter stresses. Investigation of genetic differences at the VRN-A1 locus revealed that a vernalization requirement maintained a higher level of cold response pathways while VRN-A1 genetically promoted floral development. Our results also demonstrated the influence of genetic background on the expression of cold and flowering pathways. The link between delayed shoot apex development and the induction of cold tolerance was reflected by the gradual up-regulation of abscisic acid-dependent and C-REPEAT-BINDING FACTOR pathways. This was accompanied by the down-regulation of key genes involved in meristem development as the autumn progressed. The chromosome location of differentially expressed genes between the winter and spring wheat genetic backgrounds showed a striking pattern of biased gene expression on chromosomes 6A and 6D, indicating a transcriptional regulation at the genome level. This finding adds to the complexity of the genetic cascades and gene interactions that determine the evolutionary patterns of both phenological development and cold tolerance traits in wheat.

MdHY5 positively regulates cold tolerance via CBF-dependent and CBF-independent pathways in apple

Cold stress is a major external stimulator that affects crop quality and productivity. The CBF cold regulatory pathway has been regarded as a master regulator in the response to cold stress. In this study, we found that the apple bZIP transcription factor, MdHY5, was responsive to cold treatment both at the transcriptional and at the post-translational levels. Moreover, overexpression of MdHY5 enhanced cold tolerance in apple calli and Arabidopsis. Subsequently, EMSA assay and transient expression assay demonstrated that MdHY5 positively regulated the transcript of MdCBF1 by binding to G-Box motif of its promoter. Furthermore, MdHY5 also regulated the expression of CBF-independent cold-regulated genes. Taken together, our data suggest that MdHY5 positively modulates plant cold tolerance through CBF-dependent and CBF-independent pathways, providing a deeper understanding of MdHY5-regulated cold tolerance in apple.

ABA Is Involved in Regulation of Cold Stress Response in Bermudagrass

As a representative warm-season grass, Bermudagrass [Cynodon dactylon (L). Pers.] is widely used in turf systems. However, low temperature remarkably limits its growth and distribution. ABA is a crucial phytohormone that has been reported to regulate much important physiological and biochemical processes in plants under abiotic stress. Therefore, the objective of this study was to figure out the effects of ABA on the cold-sensitive (S) and cold-resistant (R) Bermudagrass genotypes response to cold stress. In this study, the plants were treated with 100 μM ABA solution and exposed to 4°C temperature. After 7 days of cold treatment, the electrolyte leakage (EL), malonaldehyde (MDA) and H2O2 content were significantly increased in both genotypes compared with control condition, and these values were higher in R genotype than those of S genotype, respectively. By contrast, exogenous ABA application decreased the electrolyte leakage (EL), MDA and H2O2 content in both genotypes compared with those plants without ABA treatment under cold treatment condition. In addition, exogenous ABA application increased the levels of chlorophyll a fluorescence transient curve for both genotypes, and it was higher in R genotype than that of S genotype. Analysis of photosynthetic fluorescence parameters revealed that ABA treatment improved the performance of photosystem II under cold condition, particularly for the R genotype. Moreover, cold stress significantly increased δ13C values for both genotypes, while it was alleviated by exogenous ABA. Additionally, exogenous ABA application altered the expression of ABA- or cold related genes, including ABF1, CBF1, and LEA. In summary, exogenous ABA application enhanced cold resistance of both genotypes by maintaining cell membrane stability, improving the process of photosystem II, increasing carbon isotopic fractionation under cold stress, and more prominently in R genotype compared with S genotype.