Ectopic overexpression of SsCBF1, a CRT/DRE-binding factor from the nightshade plant Solanum lycopersicoides, confers freezing and salt tolerance in transgenic Arabidopsis

Wheat (Triticum aestivum. L) Plant U-box E3 ligases TaPUB2 and TaPUB3 enhance ABA response and salt stress resistance in Arabidopsis

Plant U-box E3 ligases (PUBs) are important regulators of responses to various abiotic stress conditions. In this study, we found that wheat (Triticum aestivum. L) PUBs TaPUB2 and TaPUB3 enhanced abscisic acid (ABA) responses and salt tolerance in Arabidopsis. We generated transgenic Arabidopsis lines overexpressing TaPUB2 and TaPUB3 and performed various plant physiological experiments. Overexpression of TaPUB2 and TaPUB3 increased tolerance to salinity stress in an ABA-dependent manner in transgenic plants, as evidenced by germination and survival rates, root length, stomatal aperture regulation, membrane peroxidation, photosynthetic activities, reactive oxygen species scavenging activities and expression of various ABA and salinity stress-related genes. These results demonstrate the functions of PUBs under ABA and salinity stress conditions and provide valuable information for the development of salinity stress-tolerant crop species.

Alien introgression and morpho-agronomic characterization of diploid progenies of Solanum lycopersicoides monosomic alien addition lines (MAALs) toward pre-breeding applications in tomato (S. lycopersicum)

KEY MESSAGE

Alien introgressions that were captured in the genome of diploid plants segregating from progenies of monosomic alien addition lines of S. lycopersicoides confer novel phenotypes with commercial and agronomic value in tomato breeding. Solanum lycopersicoides is a wild relative of tomato with a natural adaptation to a wide array of biotic and abiotic challenges. In this study, we identified and characterized diploid plants segregating from the progenies of monosomic alien addition lines (MAALs) of S. lycopersicoides to establish their potential as donors in breeding for target trait improvement in tomato. Molecular genotyping identified 28 of 38 MAAL progenies having the complete chromosome complement of the cultivated tomato parent and limited chromosome introgressions from the wild S. lycopersicoides parent. Analysis of SSR and indel marker profiles identified 34 unique alien introgressions in the 28 MAAL-derived introgression lines (MDILs) in the genetic background of tomato. Conserved patterns of alien introgressions were detected among sibs of MDILs 2, 3, 4 and 8. Across MDILs, a degree of preferential transmission of specific chromosome segments was also observed. Morphologically, the MDILs closely resembled the cultivated tomato more than S. lycopersicoides. The appearance of novel phenotypes in the MDILs that are lacking in the cultivated parent or the source MAALs indicates the capture of novel genetic variation by the diploid introgression lines that can add commercial and agronomic value to tomato. In particular, screening of representative MDILs for drought tolerance at the vegetative stage identified MDIL 2 and MDIL 11III as drought tolerant based on visual scoring. A regulated increase in stomatal conductance of MDIL 2 under drought stress indicates better water use efficiency that allowed it to survive for 7 days under 0% moisture level.

Intrinsic Disorder in Plant Transcription Factor Systems: Functional Implications

Eukaryotic cells are complex biological systems that depend on highly connected molecular interaction networks with intrinsically disordered proteins as essential components. Through specific examples, we relate the conformational ensemble nature of intrinsic disorder (ID) in transcription factors to functions in plants. Transcription factors contain large regulatory ID-regions with numerous orphan sequence motifs, representing potential important interaction sites. ID-regions may affect DNA-binding through electrostatic interactions or allosterically as for the bZIP transcription factors, in which the DNA-binding domains also populate ensembles of dynamic transient structures. The flexibility of ID is well-suited for interaction networks requiring efficient molecular adjustments. For example, Radical Induced Cell Death1 depends on ID in transcription factors for its numerous, structurally heterogeneous interactions, and the JAZ:MYC:MED15 regulatory unit depends on protein dynamics, including binding-associated unfolding, for regulation of jasmonate-signaling. Flexibility makes ID-regions excellent targets of posttranslational modifications. For example, the extent of phosphorylation of the NAC transcription factor SOG1 regulates target gene expression and the DNA-damage response, and phosphorylation of the AP2/ERF transcription factor DREB2A acts as a switch enabling heat-regulated degradation. ID-related phase separation is emerging as being important to transcriptional regulation with condensates functioning in storage and inactivation of transcription factors. The applicative potential of ID-regions is apparent, as removal of an ID-region of the AP2/ERF transcription factor WRI1 affects its stability and consequently oil biosynthesis. The highlighted examples show that ID plays essential functional roles in plant biology and has a promising potential in engineering.

Development of a PCR-based, genetic marker resource for the tomato-like nightshade relative, Solanum lycopersicoides using whole genome sequence analysis

Solanum lycopersicoides is a wild nightshade relative of tomato with known resistance to a wide range of pests and pathogens, as well as tolerance to cold, drought and salt stress. To effectively utilize S. lycopersicoides as a genetic resource in breeding for tomato improvement, the underlying basis of observable traits in the species needs to be understood. Molecular markers are important tools that can unlock the genetic underpinnings of phenotypic variation in wild crop relatives. Unfortunately, DNA markers that are specific to S. lycopersicoides are limited in number, distribution and polymorphism rate. In this study, we developed a suite of S. lycopersicoides-specific SSR and indel markers by sequencing, building and analyzing a draft assembly of the wild nightshade genome. Mapping of a total of 1.45 Gb of S. lycopersicoides contigs against the tomato reference genome assembled a moderate number of contiguous reads into longer scaffolds. Interrogation of the obtained draft yielded SSR information for more than 55,000 loci in S. lycopersicoides for which more than 35,000 primers pairs were designed. Additionally, indel markers were developed based on sequence alignments between S. lycopersicoides and tomato. Synthesis and experimental validation of 345 primer sets resulted in the amplification of single and multilocus targets in S. lycopersicoides and polymorphic loci between S. lycopersicoides and tomato. Cross-species amplification of the 345 markers in tomato, eggplant, silverleaf nightshade and pepper resulted in varying degrees of transferability that ranged from 55 to 83%. The markers reported in this study significantly expands the genetic marker resource for S. lycopersicoides, as well as for related Solanum spp. for applications in genetics and breeding studies.

Transgenic Breeding Approaches for Improving Abiotic Stress Tolerance: Recent Progress and Future Perspectives

The recent rapid climate changes and increasing global population have led to an increased incidence of abiotic stress and decreased crop productivity. Environmental stresses, such as temperature, drought, nutrient deficiency, salinity, and heavy metal stresses, are major challenges for agriculture, and they lead to a significant reduction in crop growth and productivity. Abiotic stress is a very complex phenomenon, involving a variety of physiological and biochemical changes in plant cells. Plants exposed to abiotic stress exhibit enhanced levels of ROS (reactive oxygen species), which are highly reactive and toxic and affect the biosynthesis of chlorophyll, photosynthetic capacity, and carbohydrate, protein, lipid, and antioxidant enzyme activities. Transgenic breeding offers a suitable alternative to conventional breeding to achieve plant genetic improvements. Over the last two decades, genetic engineering/transgenic breeding techniques demonstrated remarkable developments in manipulations of the genes for the induction of desired characteristics into transgenic plants. Transgenic approaches provide us with access to identify the candidate genes, miRNAs, and transcription factors (TFs) that are involved in specific plant processes, thus enabling an integrated knowledge of the molecular and physiological mechanisms influencing the plant tolerance and productivity. The accuracy and precision of this phenomenon assures great success in the future of plant improvements. Hence, transgenic breeding has proven to be a promising tool for abiotic stress improvement in crops. This review focuses on the potential and successful applications, recent progress, and future perspectives of transgenic breeding for improving abiotic stress tolerance and productivity in plants.

Computational Disorder Analysis in Ethylene Response Factors Uncovers Binding Motifs Critical to Their Diverse Functions

APETALA2/ETHYLENE RESPONSE FACTOR transcription factors (AP2/ERFs) play crucial roles in adaptation to stresses such as those caused by pathogens, wounding and cold. Although their name suggests a specific role in ethylene signalling, some ERF members also co-ordinate signals regulated by other key plant stress hormones such as jasmonate, abscisic acid and salicylate. We analysed a set of ERF proteins from three divergent plant species for intrinsically disorder regions containing conserved segments involved in protein–protein interaction known as Molecular Recognition Features (MoRFs). Then we correlated the MoRFs identified with a number of known functional features where these could be identified. Our analyses suggest that MoRFs, with plasticity in their disordered surroundings, are highly functional and may have been shuffled between related protein families driven by selection. A particularly important role may be played by the alpha helical component of the structured DNA binding domain to permit specificity. We also present examples of computationally identified MoRFs that have no known function and provide a valuable conceptual framework to link both disordered and ordered structural features within this family to diverse function.

Phylogenomic analysis of cytochrome P450 multigene family and their differential expression analysis in Solanum lycopersicum L. suggested tissue specific promoters

Background

Cytochrome P450 (P450) is a functionally diverse and multifamily class of enzymes which catalyses vast variety of biochemical reactions. P450 genes play regulatory role in growth, development and secondary metabolite biosynthesis. Solanum lycopersicum L. (Tomato) is an economically important crop plant and model system for various studies with massive genomic data. The comprehensive identification and characterization of P450 genes was lacking. Probing tomato genome for P450 identification would provide valuable information about the functions and evolution of the P450 gene family.

Results

In the present study, we have identified 233 P450 genes from tomato genome along with conserved motifs. Through the phylogenetic analysis of Solanum lycopersicum P450 (SlP450) protein sequences, they were classified into two major clades and nine clans further divided into 42 families. RT-qPCR analysis of selected six candidate genes were corroborated with digital expression profile. Out of 233 SlP450 genes, 73 showed expression evidence in 19 tissues of tomato. Out of 22 intron gain/loss positions, two positions were conserved in tomato P450 genes supporting intron late theory of intron evolution in SlP450 families. The comparison between tomato and other related plant P450s families showed that CYP728, CYP733, CYP80, CYP92, CYP736 and CYP749 families have been evolved in tomato and few higher plants whereas lost from Arabidopsis. The global promoter analysis of SlP450 against all the protein coding genes, coupled with expression data, revealed statistical overrepresentation of few promoter motifs in SlP450 genes which were highly expressed in specific tissue of tomato. Hence, these identified promoter motifs can be pursued further as tissue specific promoter that are driving expression of respective SlP450.

Conclusions

The phylogenetic analysis and expression profiles of tomato P450 gene family offers essential genomic resource for their functional characterization. This study allows comparison of SlP450 gene family with other Solanaceae members which are also economically important and attempt to classify functionally important SlP450 genes into groups and families. This report would enable researchers working on Tomato P450 to select appropriate candidate genes from huge repertoire of P450 genes depending on their phylogenetic class, tissue specific expression and promoter prevalence.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5483-x) contains supplementary material, which is available to authorized users.

No Time to Waste: Transcriptome Study Reveals that Drought Tolerance in Barley May Be Attributed to Stressed-Like Expression Patterns that Exist before the Occurrence of Stress

Plant survival in adverse environmental conditions requires a substantial change in the metabolism, which is reflected by the extensive transcriptome rebuilding upon the occurrence of the stress. Therefore, transcriptomic studies offer an insight into the mechanisms of plant stress responses. Here, we present the results of global gene expression profiling of roots and leaves of two barley genotypes with contrasting ability to cope with drought stress. Our analysis suggests that drought tolerance results from a certain level of transcription of stress-influenced genes that is present even before the onset of drought. Genes that predispose the plant to better drought survival play a role in the regulatory network of gene expression, including several transcription factors, translation regulators and structural components of ribosomes. An important group of genes is involved in signaling mechanisms, with significant contribution of hormone signaling pathways and an interplay between ABA, auxin, ethylene and brassinosteroid homeostasis. Signal transduction in a drought tolerant genotype may be more efficient through the expression of genes required for environmental sensing that are active already during normal water availability and are related to actin filaments and LIM domain proteins, which may function as osmotic biosensors. Better survival of drought may also be attributed to more effective processes of energy generation and more efficient chloroplasts biogenesis. Interestingly, our data suggest that several genes involved in a photosynthesis process are required for the establishment of effective drought response not only in leaves, but also in roots of barley. Thus, we propose a hypothesis that root plastids may turn into the anti-oxidative centers protecting root macromolecules from oxidative damage during drought stress. Specific genes and their potential role in building up a drought-tolerant barley phenotype is extensively discussed with special emphasis on processes that take place in barley roots. When possible, the interconnections between particular factors are emphasized to draw a broader picture of the molecular mechanisms of drought tolerance in barley.

Oil palm EgCBF3 conferred stress tolerance in transgenic tomato plants through modulation of the ethylene signaling pathway

CBF/DREB1 is a group of transcription factors that are mainly involved in abiotic stress tolerance in plants. They belong to the AP2/ERF superfamily of plant-specific transcription factors. A gene encoding a new member of this group was isolated from ripening oil palm fruit and designated as EgCBF3. The oil palm fruit demonstrates the characteristics of a climacteric fruit like tomato, in which ethylene has a major impact on the ripening process. A transgenic approach was used for functional characterization of the EgCBF3, using tomato as the model plant. The effects of ectopic expression of EgCBF3 were analyzed based on expression profiling of the ethylene biosynthesis-related genes, anti-freeze proteins (AFPs), abiotic stress tolerance and plant growth and development. The EgCBF3 tomatoes demonstrated altered phenotypes compared to the wild type tomatoes. Delayed leaf senescence and flowering, increased chlorophyll content and abnormal flowering were the consequences of overexpression of EgCBF3 in the transgenic tomatoes. The EgCBF3 tomatoes demonstrated enhanced abiotic stress tolerance under in vitro conditions. Further, transcript levels of ethylene biosynthesis-related genes, including three SlACSs and two SlACOs, were altered in the transgenic plants' leaves and roots compared to that in the wild type tomato plant. Among the eight AFPs studied in the wounded leaves of the EgCBF3 tomato plants, transcript levels of SlOSM-L, SlNP24, SlPR5L and SlTSRF1 decreased, while expression of the other four, SlCHI3, SlPR1, SlPR-P2 and SlLAP2, were up-regulated. These findings indicate the possible functions of EgCBF3 in plant growth and development as a regulator of ethylene biosynthesis-related and AFP genes, and as a stimulator of abiotic stress tolerance.

WITHDRAWN: Physiological and biochemical characterization of tomato transgenic lines overexpressing Arabidopsis thaliana cold responsive-element binding factor 3 (AtCBF3) gene under chilling stress

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Molecular Evidence for Functional Divergence and Decay of a Transcription Factor Derived from Whole-Genome Duplication in Arabidopsis thaliana

Functional divergence between duplicate transcription factors (TFs) has been linked to critical events in the evolution of land plants and can result from changes in patterns of expression, binding site divergence, and/or interactions with other proteins. Although plant TFs tend to be retained post polyploidization, many are lost within tens to hundreds of million years. Thus, it can be hypothesized that some TFs in plant genomes are in the process of becoming pseudogenes. Here, we use a pair of salt tolerance-conferring transcription factors, DWARF AND DELAYED FLOWERING1 (DDF1) and DDF2, that duplicated through paleopolyploidy 50 to 65 million years ago, as examples to illustrate potential mechanisms leading to duplicate retention and loss. We found that the expression patterns of Arabidopsis thaliana (At)DDF1 and AtDDF2 have diverged in a highly asymmetric manner, and AtDDF2 has lost most inferred ancestral stress responses. Consistent with promoter disablement, the AtDDF2 promoter has fewer predicted cis-elements and a methylated repetitive element. Through comparisons of AtDDF1, AtDDF2, and their Arabidopsis lyrata orthologs, we identified significant differences in binding affinities and binding site preference. In particular, an AtDDF2-specific substitution within the DNA-binding domain significantly reduces binding affinity. Cross-species analyses indicate that both AtDDF1 and AtDDF2 are under selective constraint, but among A. thaliana accessions, AtDDF2 has a higher level of nonsynonymous nucleotide diversity compared with AtDDF1. This may be the result of selection in different environments or may point toward the possibility of ongoing functional decay despite retention for millions of years after gene duplication.

Increased drought tolerance through the suppression of ESKMO1 gene and overexpression of CBF-related genes in Arabidopsis

Improved drought tolerance is always a highly desired trait for agricultural plants. Significantly increased drought tolerance in Arabidopsis thaliana (Columbia-0) has been achieved in our work through the suppression of ESKMO1 (ESK1) gene expression with small-interfering RNA (siRNA) and overexpression of CBF genes with constitutive gene expression. ESK1 has been identified as a gene linked to normal development of the plant vascular system, which is assumed directly related to plant drought response. By using siRNA that specifically targets ESK1, the gene expression has been reduced and drought tolerance of the plant has been enhanced dramatically in the work. However, the plant response to external abscisic acid application has not been changed. ICE1, CBF1, and CBF3 are genes involved in a well-characterized plant stress response pathway, overexpression of them in the plant has demonstrated capable to increase drought tolerance. By overexpression of these genes combining together with suppression of ESK1 gene, the significant increase of plant drought tolerance has been achieved in comparison to single gene manipulation, although the effect is not in an additive way. Accompanying the increase of drought tolerance via suppression of ESK1 gene expression, the negative effect has been observed in seeds yield of transgenic plants in normal watering conditions comparing with wide type plant.

Chilling acclimation provides immunity to stress by altering regulatory networks and inducing genes with protective functions in cassava

BACKGROUND

Stress acclimation is an effective mechanism that plants acquired for adaption to dynamic environment. Even though generally considered to be sensitive to low temperature, Cassava, a major tropical crop, can be tolerant to much lower temperature after chilling acclimation. Improvement to chilling resistance could be beneficial to breeding. However, the underlying mechanism and the effects of chilling acclimation on chilling tolerance remain largely unexplored.

RESULTS

In order to understand the mechanism of chilling acclimation, we profiled and analyzed the transcriptome and microRNAome of Cassava, using high-throughput deep sequencing, across the normal condition, a moderate chilling stress (14°C), a harsh stress (4°C) after chilling acclimation (14°C), and a chilling shock from 24°C to 4°C. The results revealed that moderate stress and chilling shock triggered comparable degrees of transcriptional perturbation, and more importantly, about two thirds of differentially expressed genes reversed their expression from up-regulation to down-regulation or vice versa in response to hash stress after experiencing moderate stress. In addition, microRNAs played important roles in the process of this massive genetic circuitry rewiring. Furthermore, function analysis revealed that chilling acclimation helped the plant develop immunity to further harsh stress by exclusively inducing genes with function for nutrient reservation therefore providing protection, whereas chilling shock induced genes with function for viral reproduction therefore causing damage.

CONCLUSIONS

Our study revealed, for the first time, the molecular basis of chilling acclimation, and showed potential regulation role of microRNA in chilling response and acclimation in Euphorbia.

Genome-wide analysis of AP2/ERF family genes from Lotus corniculatus shows LcERF054 enhances salt tolerance

Lotus corniculatus is used in agriculture as a main forage plant. Members of the Apetala2/ethylene response factor (AP2/ERF) family play important roles in regulating gene expression in response to many forms of stress, including drought and salt. Here, starting from database of the L. corniculatus var. japonicus genome, we identified 127 AP2/ERF genes by insilico cloning method. The phylogeny, gene structures, and putative conserved motifs in L. corniculatus var. japonicus ERF proteins were analyzed. Based on the number of AP2/ERF domains and the function of the genes, 127 AP2/ERF genes from L. corniculatus var. japonicus were classified into five subfamilies named the AP2, dehydration-responsive element binding factor (DREB), ERF, RAV, and a soloist. Outside the AP2/ERF domain, many L. corniculatus var. japonicus-specific conserved motifs were detected. Expression profile analysis of AP2/ERF genes by quantitative real-time PCR revealed that 19 LcERF genes, including LcERF054 (KJ004728), were significantly induced by salt stress. The results showed that the LcERF054 gene encodes a nuclear transcription activator. Overexpression of LcERF054 in Arabidopsis enhanced the tolerances to salt stress, showed higher germination ratio of seeds, and had elevated levels of relative moisture contents, soluble sugars, proline, and lower levels of malondialdehyde under stress conditions compared to wild-type plants. The expression of hyperosmotic salinity response genes COR15A, LEA4-5, P5CS1, and RD29A was found to be elevated in the LcERF054-overexpressing Arabidopsis plants compared to wild type. These results revealed that the LcERF genes play important roles in L. corniculatus cv Leo under salt stress and that LcERFs are attractive engineering targets in applied efforts to improve abiotic stress tolerances in L. corniculatus cv Leo or other crops.

Isolation and functional characterization of the ShCBF1 gene encoding a CRT/DRE-binding factor from the wild tomato species Solanum habrochaites

Plant growth and productivity are greatly affected by low ambient temperature. Complex cascades of gene expression in cold stress response are regulated by transcription factors. In this study, a cDNA clone, named ShCBF1, was isolated from Solanum habrochaites seedlings (a wild relative of cultivated tomato). It was classified as one of CBF family members based on multiple sequence alignment. The expression analysis confirmed that ShCBF1 was induced by low temperature, high salinity and drought stress. Experiments of subcellular localization in tobacco leaf cells indicated that it was localized in nucleus. Transient expression assay using onion epidermal cells revealed that the ShCBF1 protein could function similarly to AtCBF1 in activating the expression of reporter genes with a CRT/DRE element in their promoter. Moreover, ectopic overexpression of ShCBF1 in Arabidopsis enhanced freezing and high salinity tolerance of transgenic plants by improving the expression levels of some stress-responsive marker genes. Taken together, our results suggest that ShCBF1 behaves as a typical plant CBF transcription factor and might be involved in plant response to various environmental stresses.