Potato plants ectopically expressing Arabidopsis thaliana CBF3 exhibit enhanced tolerance to high-temperature stress

Genetic Basis of Potato Tuber Defects and Identification of Heat-Tolerant Clones

Heat stress during the potato growing season reduces tuber marketable yield and quality. Tuber quality deterioration includes external (heat sprouts, chained tubers, knobs) and internal (vascular discoloration, hollow heart, internal heat necrosis) tuber defects, as well as a reduction in their specific gravity and increases in reducing sugars that result in suboptimal (darker) processed products (french fries and chips). Successfully cultivating potatoes under heat-stress conditions requires planting heat-tolerant varieties that can produce high yields of marketable tubers, few external and internal tuber defects, high specific gravity, and low reducing sugars (in the case of processing potatoes). Heat tolerance is a complex trait, and understanding its genetic basis will aid in developing heat-tolerant potato varieties. A panel of 217 diverse potato clones was evaluated for yield and quality attributes in Dalhart (2019 and 2020) and Springlake (2020 and 2021), Texas, and genotyped with the Infinium 22 K V3 Potato Array. A genome-wide association study was performed to identify genomic regions associated with heat-tolerance traits using the GWASpoly package. Quantitative trait loci were identified on chromosomes 1, 3, 4, 6, 8, and 11 for external defects and on chromosomes 1, 2, 3, 10, and 11 for internal defects. Yield-related quantitative trait loci were detected on chromosomes 1, 6, and 10 pertaining to the average tuber weight and tuber number per plant. Genomic-estimated breeding values were calculated using the StageWise package. Clones with low genomic-estimated breeding values for tuber defects were identified as donors of good traits to improve heat tolerance. The identified genomic regions associated with heat-tolerance attributes and the genomic-estimated breeding values will be helpful to develop new potato cultivars with enhanced heat tolerance in potatoes.

Transcriptome Analysis Reveals Key Genes Involved in the Response of Pyrus betuleafolia to Drought and High-Temperature Stress

Drought and high-temperature stress are the main abiotic stresses that alone or simultaneously affect the yield and quality of pears worldwide. However, studies on the mechanisms of drought or high-temperature resistance in pears remain elusive. Therefore, the molecular responses of Pyrus betuleafolia, the widely used rootstock in pear production, to drought and high temperatures require further study. Here, drought- or high-temperature-resistant seedlings were selected from many Pyrus betuleafolia seedlings. The leaf samples collected before and after drought or high-temperature treatment were used to perform RNA sequencing analysis. For drought treatment, a total of 11,731 differentially expressed genes (DEGs) were identified, including 4444 drought-induced genes and 7287 drought-inhibited genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that these DEGs were more significantly enriched in plant hormone signal transduction, flavonoid biosynthesis, and glutathione metabolism. For high-temperature treatment, 9639 DEGs were identified, including 5493 significantly upregulated genes and 4146 significantly downregulated genes due to high-temperature stress. KEGG analysis showed that brassinosteroid biosynthesis, arginine metabolism, and proline metabolism were the most enriched pathways for high-temperature response. Meanwhile, the common genes that respond to both drought and high-temperature stress were subsequently identified, with a focus on responsive transcription factors, such as MYB, HSF, bZIP, and WRKY. These results reveal potential genes that function in drought or high-temperature resistance. This study provides a theoretical basis and gene resources for the genetic improvement and molecular breeding of pears.

Genome-wide identification and expression analysis of the CBF transcription factor family in Lolium perenne under abiotic stress

C-repeat binding factor (CBF) subfamily genes encoding transcriptional activators are members of the AP2/ERF superfamily. CBFs play important roles in plant tolerance to abiotic stress. In this study, we identified and analyzed the structure, phylogeny, conserved motifs, and expression profiles of 12 CBFs of the grass species Lolium perenne cultured under abiotic stress. The identified LpCBFs were grouped into three phylogenetic clades according to their protein structures and motif organizations. LpCBF expression was differentially induced by cold, heat, water deficit, salinity, and abscisic acid, among which cold treatment induced LpCBF gene expression significantly. Furthermore, association network analysis indicated that different proteins, including certain stress-related proteins, potentially interact with LpCBFs. Altogether, these findings will enhance our understanding of LpCBFs protein structure and function in the regulation of L. perenne stress responses. Our results will provide valuable information for further functional research of LpCBF proteins in L. perenne stress resistance.

Heterologous Expression of OtsB Increases Tuber Yield and Phenotypic Stability in Potato under Both Abiotic and Biotic Stresses

Climate-smart and sustainable crops are needed for the future. Engineering crops for tolerance of both abiotic and biotic stress is one approach. The accumulation of trehalose, controlled through trehalose-6-phosphate synthase (TPS) or OtsA and trehalose-6-phosphate phosphatase (TPP) or OtsB genes in microbes, is known to provide protection for many microbial and fungal species against abiotic stress. The effect of trehalose accumulation in plant species is less understood. Here, we studied the heterologous expression of Escherichia coli OtsB in potato (Solanum tuberosum var. 'Desiree') with regards to stress tolerance. The performance of transgenic lines was assessed in both growth chambers and greenhouse mesocosms. Overexpressing potato OtsB lines significantly increased resilience to heat, photoperiod, herbivory, and competition when compared with wildtype plants. Most strikingly, when subjected to high temperatures, transgenic lines exhibited a significantly lower reduction in tuber yield ranging from 40% to 77%, while wildtype plants experienced a 95% decrease in tuber yield. When exposed to competitors in a selected StSP3D::OtsB line, tuber yield was 1.6 times higher than wildtype. Furthermore, transgenic lines performed significantly better under low-nutrient regimes: under competition, yield increased by 1.5-fold. Together, these results demonstrate that increased trehalose has the potential to create more resistant and stable crop plants.

Genome-wide analysis of the AP2/ERF gene family in Tritipyrum and the response of TtERF_B2-50 in salt-tolerance

The AP2/ERF transcription factor is widely distributed across the plant kingdom and plays a crucial role in various abiotic stress responses in plants. Tritipyrum, an octoploid resulting from an intergeneric cross between Triticum aestivum (AABBDD) and Thinopyrum elongatum (EE), is a valuable source of germplasm for incorporating superior traits of Th. elongatum into T. aestivum. With the recent availability of whole -genome sequences for T. aestivum and Th. elongatum, we explored the organization and expression profiling of Tritipyrum AP2/ERF genes across the entire genome. Our investigation identified 543 Tritipyrum AP2/ERF genes, which evolutionary analysis categorized into four major groups (AP2, DREB, ERF, and RAV), whose members share a conserved motif composition. These 543 TtAP2/ERF genes were distributed throughout 28 chromosomes, with 132 duplications. Synteny analysis suggests that the AP2/ERF gene family may have a common ancestor. Transcriptome data and Real-Time PCR expression profiles revealed 43 TtAP2/ERF genes with high expression levels in response to various salt stressors and recovery regimens. Tel2E01T236300 (TtERF_B2-50) was particularly salt stress-sensitive and evolutionarily related to the salt-tolerant gene AtERF7 in A. thaliana. Pearson correlation analysis identified 689 genes positively correlated (R > 0.9) with TtERF_B2-50 expression, enriched in metabolic activities, cellular processes, stimulus response, and biological regulation. Real-time PCR showed that TtERF_B2-50 was highly expressed in roots, stems, and leaves under salt stress. These findings suggest that TtERF_B2-50 may be associated with salt stress tolerance and may serve as a valuable foreign gene for enhancing salt tolerance in wheat.

Dunaliella Ds-26-16 acts as a global regulator to enhance salt tolerance by coordinating multiple responses in Arabidopsis seedlings

MAIN CONCLUSION

Based on phenotypic, physiological and proteomic analysis, the possible mechanism by which Ds-26-16 regulates salt tolerance in Arabidopsis seedlings was revealed. Functional and mechanistic characterization of salt tolerance genes isolated from natural resources is crucial for their application. In this study, we report the possible mechanism by which Ds-26-16, a gene from Dunaliella, and its point mutation gene EP-5, enhance salt tolerance in Arabidopsis seedlings. Both Ds-26-16 and EP-5 transgenic lines displayed higher seed germination rates, cotyledon-greening rates, soluble sugar contents, decreased relative conductivity and ROS accumulation when germinating under 150 mM NaCl conditions. Comparative proteomic analysis revealed that there were 470 or 391 differentially expressed proteins (DEPs) in Ds-26-16 or EP-5, respectively, compared with the control (3301) under salt stress. The GO and KEGG enrichment analyses showed the DEPs in Ds-26-16 vs. 3301 and EP-5 vs. 3301 were similar and mainly enriched in photosynthesis, regulation of gene expression, carbohydrate metabolism, redox homeostasis, hormonal signal and defense, and regulation of seed germination. Thirty-seven proteins were found to be stably expressed under salt stress due to the expression of Ds-26-16, and eleven of them contain the CCACGT motif which could be bound by the transcription factor in ABA signaling to repress gene transcription. Taken together, we propose that Ds-26-16, as a global regulator, improves salt-tolerance by coordinating stress-induced signal transduction and modulating multiple responses in Arabidopsis seedlings. These results provide valuable information for utilizing natural resources in crop improvement for breeding salt-tolerant crops.

Knocking Out the Transcription Factor OsNAC092 Promoted Rice Drought Tolerance

Environmental drought stress threatens rice production. Previous studies have reported that related NAC (NAM, ATAF1/2, and CUC) transcription factors play an important role in drought stress. Herein, we identified and characterized OsNAC092, encoding an NAC transcription factor that is highly expressed and induced during drought tolerance. OsNAC092 knockout lines created using the clustered regularly interspaced palindromic repeats (CRISPR)-associated protein 9 (Cas9) system exhibited increased drought resistance in rice. RNA sequencing showed that the knockout of OsNAC092 caused a global expression change, and differential gene expression is chiefly associated with "response to light stimulus," "MAPK signaling pathway," "plant hormone signal transduction," "response to oxidative stress," "photosynthesis," and "water deprivation." In addition, the antioxidants and enzyme activities of the redox response were significantly increased. OsNAC092 mutant rice exhibited a higher ability to scavenge more ROS and maintained a high GSH/GSSG ratio and redox level under drought stress, which could protect cells from oxidant stress, revealing the importance of OsNAC092 in the rice's response to abiotic stress. Functional analysis of OsNAC092 will be useful to explore many rice resistance genes in molecular breeding to aid in the development of modern agriculture.

ScCBF1 plays a stronger role in cold, salt and drought tolerance than StCBF1 in potato (Solanum tuberosum)

Solanum tuberosum (St) and Solanum commersonii (Sc) are two potato varieties with different freezing tolerance. Among them, St is a freezing-sensitive variety and. Sc is a cold-resistant wild potato. CBF/DREB family members mainly function in response to freezing stress. In order to explore the different roles of St C-Repeat Binding Factor1 (StCBF1) and Sc C-Repeat Binding Factor1 (ScCBF1) in potato plants (Solanum tuberosum) under stress conditions, two kinds of potato lines were obtained with ScCBF1 and StCBF1 overexpressing respectively. Phenotypes analysis showed that both overexpressing ScCBF1 and StCBF1 caused smaller leaves, and reduced tuber yield. While the limited phenotypes of StCBF1 lines were more severe than that of ScCBF lines. After freezing treatment, StCBF1 over expression plants grown better than WT plants and worse than ScCBF1 over expression plants. Specifically, compared with wild-type lines, overexpressing ScCBF1 could up-regulate fatty acid desaturase genes, key enzyme of Calvin cycle genes, and antioxidant enzyme genes. Both ScCBF1 and StCBF1 lines showed higher PSII activity, thus maintaining a higher photosynthetic rate under cold stress. In addition, we also found that overexpression ScCBF1 and StCBF1 could also enhance the drought and salt tolerance in potato. In summary, ScCBF1 plays a stronger role in cold, salt, and drought tolerance than StCBF1 in potato (Solanum tuberosum).

Colorado potato beetle exploits frass-associated bacteria to suppress defense responses in potato plants

BACKGROUND

Colorado potato beetle (CPB; Leptinotarsa decemlineata) is a destructive quarantine pest that develops broad physiological adaptations to potato plants. During feeding, CPB deposits a copious amount of wet frass onto the surface of leaves and stems that remains in place for long periods. Insect behaviors such as feeding, crawling and oviposition are able to mediate plant defenses. However, the specific role of CPB defecation-associated cues in manipulating plant defenses remains unclear.

RESULTS

CPB larval frass significantly suppressed potato polyphenol oxidase activity and enhanced larval growth on treated potato plants. The incorporation of antibiotics into larval frass triggered higher jasmonic acid (JA)-regulated defense responses in potato plants compared with antibiotic-free frass. Four bacterial symbionts belonging to the genera Acinetobacter, Citrobacter, Enterobacter and Pantoea were isolated from larval frass and suppressed plant defenses. After reinoculation of these bacteria into axenic larvae, Acinetobacter and Citrobacter were found to be highly abundant in the frass, whereas Enterobacter and Pantoea were less abundant probably due to the negative effect of potato steroidal glycoalkaloids (SGA) such as α-solanine. Furthermore, direct application of Acinetobacter and Citrobacter to wounded potato plants significantly inhibited the expression of genes associated with the JA-mediated defense signaling pathway and SGA biosynthesis.

CONCLUSION

Our findings demonstrate that CPB exploits frass-associated bacteria as a deceptive strategy of plant defense suppression, adding an interesting dimension to our understanding of how CPB successfully specializes on potato plants. © 2022 Society of Chemical Industry.

Crosstalk between Ca2+ and Other Regulators Assists Plants in Responding to Abiotic Stress

Plants have evolved many strategies for adaptation to extreme environments. Ca²⁺, acting as an important secondary messenger in plant cells, is a signaling molecule involved in plants' response and adaptation to external stress. In plant cells, almost all kinds of abiotic stresses are able to raise cytosolic Ca²⁺ levels, and the spatiotemporal distribution of this molecule in distant cells suggests that Ca²⁺ may be a universal signal regulating different kinds of abiotic stress. Ca²⁺ is used to sense and transduce various stress signals through its downstream calcium-binding proteins, thereby inducing a series of biochemical reactions to adapt to or resist various stresses. This review summarizes the roles and molecular mechanisms of cytosolic Ca²⁺ in response to abiotic stresses such as drought, high salinity, ultraviolet light, heavy metals, waterlogging, extreme temperature and wounding. Furthermore, we focused on the crosstalk between Ca²⁺ and other signaling molecules in plants suffering from extreme environmental stress.

Overexpression of ZmDHN11 could enhance transgenic yeast and tobacco tolerance to osmotic stress

KEY MESSAGE

Maize group II LEA protein ZmDHN11 could protect protein activity and confer resistance to osmotic stress on transgenic yeast and tobacco. Late embryogenesis abundant (LEA) proteins are widely assumed to play crucial roles in environmental stress tolerance, but their function has remained obscure. Dehydrins are group II LEA proteins, which are highly hydrophilic plant stress proteins. In the present study, a novel group II LEA protein, ZmDHN11, was cloned and identified from maize. The expression of ZmDHN11 was induced by high osmotic stress, low temperature, salinity, and ABA (abscisic acid). The ZmDHN11 protein specifically accumulated in the nuclei and cytosol. Further study indicated that ZmDHN11 is phosphorylated by the casein kinase CKII. ZmDHN11 protected the activity of LDH under water-deficit stress. The overexpression of ZmDHN11 endows transgenic yeast and tobacco with tolerance to osmotic stress.

NAC Transcription Factor PwNAC11 Activates ERD1 by Interaction with ABF3 and DREB2A to Enhance Drought Tolerance in Transgenic Arabidopsis

NAC (NAM, ATAF1/2, and CUC2) transcription factors are ubiquitously distributed in eukaryotes and play significant roles in stress response. However, the functional verifications of NACs in Picea (P.) wilsonii remain largely uncharacterized. Here, we identified the NAC transcription factor PwNAC11 as a mediator of drought stress, which was significantly upregulated in P. wilsonii under drought and abscisic acid (ABA) treatments. Yeast two-hybrid assays showed that both the full length and C-terminal of PwNAC11 had transcriptional activation activity and PwNAC11 protein cannot form a homodimer by itself. Subcellular observation demonstrated that PwNAC11 protein was located in nucleus. The overexpression of PwNAC11 in Arabidopsis obviously improved the tolerance to drought stress but delayed flowering time under nonstress conditions. The steady-state level of antioxidant enzymes' activities and light energy conversion efficiency were significantly increased in PwNAC11 transgenic lines under dehydration compared to wild plants. PwNAC11 transgenic lines showed hypersensitivity to ABA and PwNAC11 activated the expression of the downstream gene ERD1 by binding to ABA-responsive elements (ABREs) instead of drought-responsive elements (DREs). Genetic evidence demonstrated that PwNAC11 physically interacted with an ABA-induced protein-ABRE Binding Factor3 (ABF3)-and promoted the activation of ERD1 promoter, which implied an ABA-dependent signaling cascade controlled by PwNAC11. In addition, qRT-PCR and yeast assays showed that an ABA-independent gene-DREB2A-was also probably involved in PwNAC11-mediated drought stress response. Taken together, our results provide the evidence that PwNAC11 plays a dominant role in plants positively responding to early drought stress and ABF3 and DREB2A synergistically regulate the expression of ERD1.

Glycinebetaine mitigated the photoinhibition of photosystem II at high temperature in transgenic tomato plants

Photosystem II (PSII), especially the D1 protein, is highly sensitive to the detrimental impact of heat stress. Photoinhibition always occurs when the rate of photodamage exceeds the rate of D1 protein repair. Here, genetically engineered codA-tomato with the capability to accumulate glycinebetaine (GB) was established. After photoinhibition treatment at high temperature, the transgenic lines displayed more thermotolerance to heat-induced photoinhibition than the control line. GB maintained high expression of LeFtsHs and LeDegs and degraded the damaged D1 protein in time. Meanwhile, the increased transcription of synthesis-related genes accelerated the de novo synthesis of D1 protein. Low ROS accumulation reduced the inhibition of D1 protein translation in the transgenic plants, thereby reducing protein damage. The increased D1 protein content and decreased phosphorylated D1 protein (pD1) in the transgenic plants compared with control plants imply that GB may minimize photodamage and maximize D1 protein stability. As D1 protein exhibits a high turnover, PSII maybe repaired rapidly and efficiently in transgenic plants under photoinhibition treatment at high temperature, with the resultant mitigation of photoinhibition of PSII.

Evolutionary history of the C-repeat binding factor/dehydration-responsive element-binding 1 (CBF/DREB1) protein family in 43 plant species and characterization of CBF/DREB1 proteins in Solanum tuberosum

Background

Plants are easily affected by temperature variations, and high temperature (heat stress) and low temperature (cold stress) will lead to poor plant development and reduce crop yields. Therefore, it is very important to identify resistance genes for improving the ability of plants to resist heat stress or cold stress by using modern biotechnology. Members of the C-repeat binding factor/Dehydration responsive element-binding 1 (CBF/DREB1) protein family are related to the stress resistance of many plant species. These proteins affect the growth and development of plants and play vital roles during environmental stress (cold, heat, drought, salt, etc.). In this study, we identified CBF/DREB1 genes from 43 plant species (including algae, moss, ferns, gymnosperms, angiosperms) by using bioinformatic methods to clarify the characteristics of the CBF/DREB1 protein family members and their functions in potato under heat and cold stresses.

Results

In this study, we identified 292 CBF/DREB1 proteins from 43 plant species. However, no CBF/DREB1 protein was found in algae, moss, ferns, or gymnosperms; members of this protein family exist only in angiosperms. Phylogenetic analysis of all the CBF/DREB1 proteins revealed five independent groups. Among them, the genes of group I do not exist in eudicots and are found only in monocots, indicating that these genes have a special effect on monocots. The analysis of motifs, gene duplication events, and the expression data from the PGSC website revealed the gene structures, evolutionary relationships, and expression patterns of the CBF/DREB1 proteins. In addition, analysis of the transcript levels of the 8 CBF/DREB1 genes in potato (Solanum tuberosum) under low-temperature and high-temperature stresses showed that these genes were related to temperature stresses. In particular, the expression levels of StCBF3 and StCBF4 in the leaves, stems, and roots significantly increased under high-temperature conditions, which suggested that StCBF3 and StCBF4 may be closely related to heat tolerance in potato.

Conclusion

Overall, members of the CBF/DREB1 protein family exist only in angiosperms and plays an important role in the growth and development of plants. In addition, the CBF/DREB1 protein family is related to the heat and cold resistance of potato. Our research revealed the evolution of the CBF/DREB1 family, and is useful for studying the precise functions of the CBF/DREB1 proteins when the plants are developing and are under temperature stress.

Chloroplastic Os3BGlu6 contributes significantly to cellular ABA pools and impacts drought tolerance and photosynthesis in rice

Cellular abscisic acid (ABA) concentration is determined by both de novo biosynthesis and recycling via β-glucosidase(s). However, which rice β-glucosidase(s) are involved in this process remains unknown. Here, we report on a chloroplastic β-glucosidase isoenzyme, Os3BGlu6, that functions in ABA recycling in rice. Disruption of Os3BGlu6 in rice resulted in dwarfism, lower ABA content in leaves, drought-sensitivity, lower photosynthesis rate and higher intercellular CO₂ concentration. Os3BGlu6 could hydrolyze ABA-GE to ABA in vitro. The reversion and overexpression rice lines restored or increased the drought tolerance as shown by the higher β-glucosidase activity, ABA concentrations and expressions of ABA- and drought-responsive genes. Drought induced Os3BGlu6 to form dimers, and the degree of polymerization correlated well with the increase in cellular ABA concentrations and drought tolerance in rice. Os3BGlu6 was responsive to drought and ABA treatments, and the protein was localized to the chloroplast. Disruption of Os3BGlu6 resulted in the increased stomatal density and impaired stomatal movement. Transcriptomics revealed that disruption of Os3BGlu6 resulted in chloroplastic oxidative stress and lowered Rubisco activity even under normal conditions. Taken together, these results suggest that chloroplastically localized Os3BGlu6 significantly affects cellular ABA pools, thereby affecting drought tolerance and photosynthesis in rice.

Assessment of Local and Systemic Changes in Plant Gene Expression and Aphid Responses during Potato Interactions with Arbuscular Mycorrhizal Fungi and Potato Aphids

This research examined aphid and plant responses to distinct levels (none, low, and high) of arbuscular mycorrhizal (AM) fungal root colonization by studying the association between potato aphids (Macrosiphum euphorbiae), potatoes (Solanum tuberosum), and AM fungi (Rhizophagus intraradices). It extends knowledge on gene expression changes, assessed by RT-qPCR, of ten defense-related genes at two time-points post-herbivory (24 h and 10 days), focusing on aphid-infested local leaves, non-infested systemic leaves, and roots. The results showed that aphid fitness was not altered by AM symbiosis. At 24 h, ETHYLENE RECEPTOR 1 gene expression was repressed in roots of aphid-infested non-mycorrhizal plants and aphid-infested plants with a high level of AM fungal root colonization, but not on aphid-infested plants with a low level of AM fungal root colonization. At 10 days, ALLENE OXIDE CYCLASE and POTATO TYPE I PROTEASE INHIBITOR were upregulated exclusively in local leaves of aphid-infested plants with a low level of AM fungal root colonization. In addition, local and systemic changes in plant gene expression appeared to be regulated exclusively by AM status and aphid herbivory. In summary, the gene expression data provide insights on mycorrhizal potato responses to aphid herbivory and serve as a starting point for future studies using this system.

Climatic changes and potatoes: How can we cope with the abiotic stresses?

Climate change triggers increases in temperature, drought, and/or salinity that threaten potato production, because they necessitate specific amounts and quality of water, meanwhile lower temperatures generally support stable crop yields. Various cultivation techniques have been developed to reduce the negative effects of drought, heat and/or salinity stresses on potato. Developing innovative varieties with relevant tolerance to abiotic stress is absolutely necessary to guarantee competitive production under sub-optimal environments. Commercial varieties are sensitive to abiotic stresses, and substantial changes to their higher tolerance levels are not easily achieved because their genetic base is narrow. Nonetheless, there are several other possibilities for genetic enhancement using landraces and wild relatives. The complexity of polysomic genetics and heterozygosity in potato hamper the phenotype evaluation over abiotic stresses and consequent conventional introgression of tolerance traits, which are more challenging than previous successes shown over diseases and insects resistances. Today, potatoes face more challenges with severe abiotic stresses. Potato wild relatives can be explored further using innovative genomic, transcriptomic, proteomic, and metabolomic approaches. At the field level, appropriate cultivation techniques must be applied along with precision farming technology and tolerant varieties developed from various breeding techniques, in order to realize high yield under multiple stresses.

Characterization and expression profiling of the ICE-CBF-COR genes in wheat

Cold stress is one of the major abiotic stresses that limit crop production. The ICE-CBF-COR pathway is associated with cold stress response in a wide variety of crop species. However, the ICE-CBF-COR genes has not been well characterized in wheat (Triticum aestivum). This study identified, characterized and examined the expression profiles of the ICE, CBF and COR genes for cold defense in wheat. Five ICE (inducer of CBF expression) genes, 37 CBF (C-repeat binding factor) genes and 11 COR (cold-responsive or cold-regulated) genes were discovered in the wheat genome database. Phylogenetic trees based on all 53 genes revealed that CBF genes were more diverse than ICE and COR genes. Twenty-two of the 53 genes appeared to include 11 duplicated pairs. Twenty rice (Oryza sativa) genes and 21 sorghum (Sorghum bicolor) and maize (Zea mays) genes showed collinearity with the wheat ICE, CBF and COR genes. Transcriptome data and qRT-PCR analyses revealed tissue-specific expression patterns of the ICE, CBF and COR genes, and identified similarities in the expression pattern of genes from the same family when subjected to drought, heat, drought plus heat, and cold stress. These results provide information for better understanding the biological roles of ICE, CBF, COR genes in wheat.

The expanding roles of APETALA2/Ethylene Responsive Factors and their potential applications in crop improvement

Understanding the molecular basis of the gene-regulatory networks underlying agronomic traits or plant responses to abiotic/biotic stresses is very important for crop improvement. In this context, transcription factors, which either singularly or in conjugation directly control the expression of many target genes, are suitable candidates for improving agronomic traits via genetic engineering. In this regard, members of one of the largest class of plant-specific APETALA2/Ethylene Response Factor (AP2/ERF) superfamily, which is implicated in various aspects of development and plant stress adaptation responses, are considered high-value targets for crop improvement. Besides their long-known regulatory roles in mediating plant responses to abiotic stresses such as drought and submergence, the novel roles of AP2/ERFs during fruit ripening or secondary metabolites production have also recently emerged. The astounding functional plasticity of AP2/ERF members is considered to be achieved by their interplay with other regulatory networks and signalling pathways. In this review, we have integrated the recently accumulated evidence from functional genomics studies and described their newly emerged functions in plants. The key structural features of AP2/ERF proteins and the modes of their action are briefly summarized. The importance of AP2/ERFs in plant development and stress responses and a summary of the event of their successful applications in crop improvement programs are also provided. Altogether, we envisage that the synthesized information presented in this review will be useful to design effective strategies for improving agronomic traits in crop plants.

Mycorrhiza-Induced Resistance in Potato Involves Priming of Defense Responses Against Cabbage Looper (Noctuidae: Lepidoptera)

Most plants form mutualistic associations with arbuscular mycorrhizal (AM) fungi that are ubiquitous in soils. Through this symbiosis, plants can withstand abiotic and biotic stresses. The underlying molecular mechanisms involved in mediating mycorrhiza-induced resistance against insects needs further research, and this is particularly true for potato (Solanum tuberosum L. (Solanales: Solanaceae)), which is the fourth most important crop worldwide. In this study, the tripartite interaction between potato, the AM fungus Rhizophagus irregularis (Glomerales: Glomeraceae), and cabbage looper (Trichoplusia ni Hübner) (Lepidoptera: Noctuidae) was examined to determine whether potato exhibits mycorrhiza-induced resistance against this insect. Plant growth, insect fitness, AM fungal colonization of roots, and transcript levels of defense-related genes were measured in shoots and roots after 5 and 8 d of herbivory on mycorrhizal and nonmycorrhizal plants. AM fungal colonization of roots did not have an effect on potato growth, but root colonization levels increased by herbivory. Larval weight gain was reduced after 8 d of feeding on mycorrhizal plants compared with nonmycorrhizal plants. Systemic upregulation of Allene Oxide Synthase 1 (AOS1), 12-Oxo-Phytodienoate Reductase 3 (OPR3) (jasmonic acid pathway), Protease Inhibitor Type I (PI-I) (anti-herbivore defense), and Phenylalanine Ammonia Lyase (PAL) transcripts (phenylpropanoid pathway) was found during the tripartite interaction. Together, these findings suggest that potato may exhibit mycorrhiza-induced resistance to cabbage looper by priming anti-herbivore defenses aboveground. This study illustrates how mycorrhizal potato responds to herbivory by a generalist-chewing insect and serves as the basis for future studies involving tripartite interactions with other pests.

Ectopic expression of StCBF1and ScCBF1 have different functions in response to freezing and drought stresses in Arabidopsis

Solanum tuberosum potato species constitute the bulk of economically and agronomically important potato production. However, S. tuberosum is a drought- and frost-sensitive species that is incapable of acclimating to the cold. Solanum commersonii is a tuber-bearing wild potato species that exhibits greater frost and drought resistance than S. tuberosum. CBF/DREB (C-REPET BINDING FACTOR/DROUGHT RESPONSE ELEMENT BINGING FACTOR) transcription factors play important roles in response to a variety of abiotic stresses, such as cold, drought and salt stresses. To explore different functions between S. tuberosum CBF1 (StCBF1) and S. commersonii CBF1 (ScCBF1), Arabidopsis was transformed with the ScCBF1 and StCBF1 genes driven by a constitutive CaMV35S promoter. Our results reveal that the ScCBF1 transgenic lines are much more tolerant to freezing and drought than the StCBF1 transgenic lines. The development of transgenic plants was altered, resulting in dwarf phenotype with delayed flowering and thicker and additional rosette leaves. The expression levels of several COR (COLD-RESPONSIVE) genes and development-related genes, including genes that inhibited plant growth (GA2ox7, RGL3) and delayed flowering (FLC) were higher in transgenic plants. These results suggest that these two potato CBF1 play important roles in the plant response to abiotic stress and can influence plant growth and development, and ScCBF1 plays a more pronounced function than StCBF1.

Comparative Transcriptome Analyses Reveal Potential Mechanisms of Enhanced Drought Tolerance in Transgenic Salvia Miltiorrhiza Plants Expressing AtDREB1A from Arabidopsis

In our previous study, drought-resistant transgenic plants of Salvia miltiorrhiza were produced via overexpression of the transcription factor AtDREB1A. To unravel the molecular mechanisms underpinning elevated drought tolerance in transgenic plants, in the present study we compared the global transcriptional profiles of wild-type (WT) and AtDREB1A-expressing transgenic plants using RNA-sequencing (RNA-seq). Using cluster analysis, we identified 3904 differentially expressed genes (DEGs). Compared with WT plants, 423 unigenes were up-regulated in pRD29A::AtDREB1A-31 before drought treatment, while 936 were down-regulated and 1580 and 1313 unigenes were up- and down-regulated after six days of drought. COG analysis revealed that the 'signal transduction mechanisms' category was highly enriched among these DEGs both before and after drought stress. Based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation, DEGs associated with "ribosome", "plant hormone signal transduction", photosynthesis", "plant-pathogen interaction", "glycolysis/gluconeogenesis" and "carbon fixation" are hypothesized to perform major functions in drought resistance in AtDREB1A-expressing transgenic plants. Furthermore, the number of DEGs associated with different transcription factors increased significantly after drought stress, especially the AP2/ERF, bZIP and MYB protein families. Taken together, this study substantially expands the transcriptomic information for S. miltiorrhiza and provides valuable clues for elucidating the mechanism of AtDREB1A-mediated drought tolerance in transgenic plants.

Overexpressing IbCBF3 increases low temperature and drought stress tolerance in transgenic sweetpotato

Dehydration-responsive element-binding/C-repeat-binding factor (DREB/CBF) proteins regulate the transcription of genes involved in cold acclimation in several species. However, little is known about the physiological functions of CBF proteins in the low temperature-sensitive crop sweetpotato. We previously reported that the DREB1/CBF-like sweetpotato gene SwDREB1/IbCBF3 is involved in responses to diverse abiotic stresses. In this study, we confirmed that IbCBF3 is localized to the nucleus and binds to the C-repeat/dehydration-responsive elements (CRT/DRE) in the promoters of cold-regulated (COR) genes. We generated transgenic sweetpotato plants overexpressing IbCBF3 under the control of the CaMV 35S promoter (referred to as SC plants) and evaluated their responses to various abiotic stresses. IbCBF3 expression was dramatically induced by cold and drought but much less strongly induced by high salinity and ABA. We further characterized two SC lines (SC3 and SC6) with high levels of IbCBF3 transcript. The SC plants displayed enhanced tolerance to cold, drought, and oxidative stress on the whole-plant level. Under cold stress treatment (4 °C for 48 h), severe wilting and chilling injury were observed in the leaves of wild-type (WT) plants, whereas SC plants were not affected by cold stress. In addition, the COR genes were significantly upregulated in SC plants compared with the WT. The SC plants also showed significantly higher tolerance to drought stress than the WT, which was associated with higher photosynthesis efficiency and lower hydrogen peroxide levels. These results indicate that IbCBF3 is a functional transcription factor involved in the responses to various abiotic stresses in sweetpotato.

Modulating AtDREB1C Expression Improves Drought Tolerance in Salvia miltiorrhiza

Dehydration responsive element binding proteins are transcription factors of the plant-specific AP2 family, many of which contribute to abiotic stress responses in several plant species. We investigated the possibility of increasing drought tolerance in the traditional Chinese medicinal herb, Salvia miltiorrhiza, through modulating the transcriptional regulation of AtDREB1C in transgenic plants under the control of a constitutive (35S) or drought-inducible (RD29A) promoter. AtDREB1C transgenic S. miltiorrhiza plants showed increased survival under severe drought conditions compared to the non-transgenic wild-type (WT) control. However, transgenic plants with constitutive overexpression of AtDREB1C showed considerable dwarfing relative to WT. Physiological tests suggested that the higher chlorophyll content, photosynthetic capacity, and superoxide dismutase, peroxidase, and catalase activity in the transgenic plants enhanced plant drought stress resistance compared to WT. Transcriptome analysis of S. miltiorrhiza following drought stress identified a number of differentially expressed genes (DEGs) between the AtDREB1C transgenic lines and WT. These DEGs are involved in photosynthesis, plant hormone signal transduction, phenylpropanoid biosynthesis, ribosome, starch and sucrose metabolism, and other metabolic pathways. The modified pathways involved in plant hormone signaling are thought to be one of the main causes of the increased drought tolerance of AtDREB1C transgenic S. miltiorrhiza plants.

Reverse Genetics and High Throughput Sequencing Methodologies for Plant Functional Genomics

In the post-genomic era, increasingly sophisticated genetic tools are being developed with the long-term goal of understanding how the coordinated activity of genes gives rise to a complex organism. With the advent of the next generation sequencing associated with effective computational approaches, wide variety of plant species have been fully sequenced giving a wealth of data sequence information on structure and organization of plant genomes. Since thousands of gene sequences are already known, recently developed functional genomics approaches provide powerful tools to analyze plant gene functions through various gene manipulation technologies. Integration of different omics platforms along with gene annotation and computational analysis may elucidate a complete view in a system biology level. Extensive investigations on reverse genetics methodologies were deployed for assigning biological function to a specific gene or gene product. We provide here an updated overview of these high throughout strategies highlighting recent advances in the knowledge of functional genomics in plants.

Genome-wide analysis of the Hsp70 family genes in pepper (Capsicum annuum L.) and functional identification of CaHsp70-2 involvement in heat stress

Hsp70s function as molecular chaperones and are encoded by a multi-gene family whose members play a crucial role in plant response to stress conditions, and in plant growth and development. Pepper (Capsicum annuum L.) is an important vegetable crop whose genome has been sequenced. Nonetheless, no overall analysis of the Hsp70 gene family is reported in this crop plant to date. To assess the functionality of Capsicum annuum Hsp70 (CaHsp70) genes, pepper genome database was analyzed in this research. A total of 21 CaHsp70 genes were identified and their characteristics were also described. The promoter and transcript expression analysis revealed that CaHsp70s were involved in pepper growth and development, and heat stress response. Ectopic expression of a cytosolic gene, CaHsp70-2, regulated expression of stress-related genes and conferred increased thermotolerance in transgenic Arabidopsis. Taken together, our results provide the basis for further studied to dissect CaHsp70s' function in response to heat stress as well as other environmental stresses.

Ectopic Expression of DREB Transcription Factor, AtDREB1A, Confers Tolerance to Drought in Transgenic Salvia miltiorrhiza

Drought decreases crop productivity more than any other type of environmental stress. Transcription factors (TFs) play crucial roles in regulating plant abiotic stress responses. The Arabidopsis thaliana gene DREB1A/CBF3, encoding a stress-inducible TF, was introduced into Salvia miltiorrhiza Ectopic expression of AtDREB1A resulted in increased drought tolerance, and transgenic lines had higher relative water content and Chl content, and exhibited an increased photosynthetic rate when subjected to drought stress. AtDREB1A transgenic plants generally displayed lower malondialdehyde (MDA), but higher superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities under drought stress. In particular, plants with ectopic AtDREB1A expression under the control of the stress-induced RD29A promoter exhibited more tolerance to drought compared with p35S::AtDREB1A transgenic plants, without growth inhibition or phenotypic aberrations. Differential gene expression profiling of wild-type and pRD29A::AtDREB1A transgenic plants following drought stress revealed that the expression levels of various genes associated with the stress response, photosynthesis, signaling, carbohydrate metabolism and protein protection were substantially higher in transgenic plants. In addition, the amount of salvianolic acids and tanshinones was significantly elevated in AtDREB1A transgenic S. miltiorrhiza roots, and most of the genes in the related biosynthetic pathways were up-regulated. Together, these results demonstrated that inducing the expression of a TF can effectively regulate multiple genes in the stress response pathways and significantly improve the resistance of plants to abiotic stresses. Our results also suggest that genetic manipulation of a TF can improve production of valuable secondary metabolites by regulating genes in associated pathways.

Arabidopsis DREB1B in transgenic Salvia miltiorrhiza increased tolerance to drought stress without stunting growth

Multiple stress response genes are controlled by transcription factors in a coordinated manner; therefore, these factors can be used for molecular plant breeding. CBF1/DREB1B, a known stress-inducible gene, was isolated from Arabidopsis thaliana and introduced into Salvia miltiorrhiza under the control of the CaMV35S or RD29A promoter. Under drought stress, relative water content, chlorophyll content, and the net photosynthetic rate were observed to be higher in the transgenic lines than in the wild type (WT). Moreover, O2(-) and H2O2 accumulation was observed to be lower in the transgenic lines. Additional analyses revealed that the AtDREB1B transgenic plants generally displayed lesser malondialdehyde (MDA) but higher superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities than the WT under drought stress. Quantitative real-time polymerase chain reaction of a subset of genes involved in photosynthesis, stress response, carbohydrate metabolism, and cell protection further verified that AtDREB1B could enhance tolerance to drought by activating different downstream DREB/CBF genes in the transgenic plants. Furthermore, no growth inhibition was detected in transgenic S. miltiorrhiza plants that expressed AtDREB1B driven by either the constitutive CaMV35S promoter or the stress-inducible RD29A promoter. Together, these results suggest that AtDREB1B is a good candidate gene for increasing drought tolerance in transgenic S. miltiorrhiza.

Salvaging effect of triacontanol on plant growth, thermotolerance, macro-nutrient content, amino acid concentration and modulation of defense hormonal levels under heat stress

In this study, it was hypothesized that application of triacontanol, a ubiquitous saturated primary alcohol, at different times-before (TBHS), mid (TMHS), and after (TAHS) heat stress-will extend heat stress (HS) protection in mungbean. The effect of triacontanol on the levels of defense hormones abscisic acid (ABA) and jasmonic acid (JA) was investigated along with the plant growth promotion, nutrient and amino acid content with and without heat stress. Heat stress caused a prominent reduction in plant growth attributes, nutrient and amino acid content, which were attributed to the decreased level of ABA and JA. However, application of triacontanol, particularly in the TBHS and TMHS treatments, reversed the deleterious effects of HS by showing increased ABA and JA levels that favored the significant increase in plant growth attributes, enhanced nutrient content, and high amount of amino acid. TAHS, a short-term application of triacontanol, also significantly increased ABA and JA levels and thus revealed important information of its association with hormonal modulation. The growth-promoting effect of triacontanol was also confirmed under normal growth conditions. To the best of our knowledge, this study is the first to demonstrate the beneficial effects of triacontanol, with or without heat stress, on mungbean and its interaction with or regulation of the levels of defense hormones.