Stable transgene expression and random gene silencing in wheat

The vascular targeted citrus FLOWERING LOCUS T3 gene promotes non-inductive early flowering in transgenic Carrizo rootstocks and grafted juvenile scions

Shortening the juvenile stage in citrus and inducing early flowering has been the focus of several citrus genetic improvement programs. FLOWERING LOCUS T (FT) is a small phloem-translocated protein that regulates precocious flowering. In this study, two populations of transgenic Carrizo citrange rootstocks expressing either Citrus clementina FT1 or FT3 genes under the control of the Arabidopsis thaliana phloem specific SUCROSE SYNTHASE 2 (AtSUC2) promoter were developed. The transgenic plants were morphologically similar to the non-transgenic controls (non-transgenic Carrizo citrange), however, only AtSUC2-CcFT3 was capable of inducing precocious flowers. The transgenic lines produced flowers 16 months after transformation and flower buds appeared 30-40 days on juvenile immature scions grafted onto transgenic rootstock. Gene expression analysis revealed that the expression of SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and APETALA1 (AP1) were enhanced in the transgenics. Transcriptome profiling of a selected transgenic line showed the induction of genes in different groups including: genes from the flowering induction pathway, APETALA2/ETHYLENE RESPONSE FACTOR (AP2/ERF) family genes, and jasmonic acid (JA) pathway genes. Altogether, our results suggested that ectopic expression of CcFT3 in phloem tissues of Carrizo citrange triggered the expression of several genes to mediate early flowering.

Biolistic Transformation of Japonica Rice Varieties

Genetic improvement of rice is crucial to achieve global food security as rice is an important staple crop for more than half of the global population. One of the methodologies for genetic improvement is biolistic delivery of genetic components into plant cells. In this chapter, we describe steps involved in introducing plasmid DNA carrying gene of interest into rice mature embryos using Biolistic^® PDS-1000/He particle delivery system. We also provide information required for recovery of transformed plants and production of transgenic seed for next generation analysis. Using this protocol, typical 50-70 putative independent transgenic callus lines can be generated from 100 bombarded embryos. Transgenic rice plantlets can be produced within 2 months after the initiation of seed germination for transformation.

Nanobiolistics: An Emerging Genetic Transformation Approach

Biolistic delivery of biomolecular cargoes to plants with micron-scale projectiles is a well-established technique in plant biotechnology. However, the relatively large micron-scale biolistic projectiles can result in tissue damage, low regeneration efficiency, and create difficulties for the biolistic transformation of isomorphic small cells or subcellular target organelles (i.e., mitochondria and plastids). As an alternative to micron-sized carriers, nanomaterials provide a promising approach for biomolecule delivery to plants. While most studies exploring nanoscale biolistic carriers have been carried out in animal cells and tissues, which lack a cell wall, we can nonetheless extrapolate their utility for nanobiolistic delivery of biomolecules in plant targets. Specifically, nanobiolistics has shown promising results for use in animal systems, in which nanoscale projectiles yield lower levels of cell and tissue damage while maintaining similar transformation efficiencies as their micron-scale counterparts. In this chapter, we specifically discuss biolistic delivery of nanoparticles for plant genetic transformation purposes and identify the figures of merit requiring optimization for broad-scale implementation of nanobiolistics in plant genetic transformations.

Mutagenesis of Puccinia graminis f. sp. tritici and Selection of Gain-of-Virulence Mutants

Wheat stem rust caused by the fungus Puccinia graminis f. sp. tritici (Pgt), is regaining prominence due to the recent emergence of virulent isolates and epidemics in Africa, Europe and Central Asia. The development and deployment of wheat cultivars with multiple stem rust resistance (Sr) genes stacked together will provide durable resistance. However, certain disease resistance genes can suppress each other or fail in particular genetic backgrounds. Therefore, the function of each Sr gene must be confirmed after incorporation into an Sr-gene stack. This is difficult when using pathogen disease assays due to epistasis from recognition of multiple avirulence (Avr) effectors. Heterologous delivery of single Avr effectors can circumvent this limitation, but this strategy is currently limited by the paucity of cloned Pgt Avrs. To accelerate Avr gene cloning, we outline a procedure to develop a mutant population of Pgt spores and select for gain-of-virulence mutants. We used ethyl methanesulphonate (EMS) to mutagenize urediniospores and create a library of > 10,000 independent mutant isolates that were combined into 16 bulks of ~658 pustules each. We sequenced random mutants and determined the average mutation density to be 1 single nucleotide variant (SNV) per 258 kb. From this, we calculated that a minimum of three independently derived gain-of-virulence mutants is required to identify a given Avr gene. We inoculated the mutant library onto plants containing Sr43, Sr44, or Sr45 and obtained 9, 4, and 14 mutants with virulence toward Sr43, Sr44, or Sr45, respectively. However, only mutants identified on Sr43 and Sr45 maintained their virulence when reinolculated onto the lines from which they were identified. We further characterized 8 mutants with virulence toward Sr43. These also maintained their virulence profile on the stem rust international differential set containing 20 Sr genes, indicating that they were most likely not accidental contaminants. In conclusion, our method allows selecting for virulent mutants toward targeted resistance (R) genes. The development of a mutant library from as little as 320 mg spores creates a resource that enables screening against several R genes without the need for multiple rounds of spore multiplication and mutagenesis.

A deletion mutation in TaHRC confers Fhb1 resistance to Fusarium head blight in wheat

Fusarium head blight (FHB), which is mainly caused by Fusarium graminearum, is a destructive wheat disease that threatens global wheat production. Fhb1, a quantitative trait locus discovered in Chinese germplasm, provides the most stable and the largest effect on FHB resistance in wheat. Here we show that TaHRC, a gene that encodes a putative histidine-rich calcium-binding protein, is the key determinant of Fhb1-mediated resistance to FHB. We demonstrate that TaHRC encodes a nuclear protein conferring FHB susceptibility and that a deletion spanning the start codon of this gene results in FHB resistance. Identical sequences of the TaHRC-R allele in diverse accessions indicate that Fhb1 had a single origin, and phylogenetic and haplotype analyses suggest that the TaHRC-R allele most likely originated from a line carrying the Dahongpao haplotype. This discovery opens a new avenue to improve FHB resistance in wheat, and possibly in other cereal crops, by manipulating TaHRC sequence through bioengineering approaches.

Chromosome Arm Locations of Barley Sucrose Transporter Gene in Transgenic Winter Wheat Lines

Three transgenic HOSUT lines of winter wheat, HOSUT12, HOSUT20, and HOSUT24, each harbor a single copy of the cDNA for the barley sucrose transporter gene HvSUT1 (SUT), which was fused to the barley endosperm-specific Hordein B1 promoter (HO; the HOSUT transgene). Previously, flow cytometry combined with PCR analysis demonstrated that the HOSUT transgene had been integrated into different wheat chromosomes: 7A, 5D, and 4A in HOSUT12, HOSUT20, and HOSUT24, respectively. In order to confirm the chromosomal location of the HOSUT transgene by a cytological approach using wheat aneuploid stocks, we crossed corresponding nullisomic-tetrasomic lines with the three HOSUT lines, namely nullisomic 7A-tetrasomic 7B with HOSUT12, nullisomic 5D-tetrasomic 5B with HOSUT20, and nullisomic 4A-tetrasomic 4B with HOSUT24. We examined the resulting chromosomal constitutions and the presence of the HOSUT transgene in the F₂ progeny by means of chromosome banding and PCR. The chromosome banding patterns of the critical chromosomes in the original HOSUT lines showed no difference from those of the corresponding wild type chromosomes. The presence or absence of the critical chromosomes completely corresponded to the presence or absence of the HOSUT transgene in the F₂ plants. Investigating telocentric chromosomes occurred in the F₂ progeny, which were derived from the respective critical HOSUT chromosomes, we found that the HOSUT transgene was individually integrated on the long arms of chromosomes 4A, 7A, and 5D in the three HOSUT lines. Thus, in this study we verified the chromosomal locations of the transgene, which had previously been determined by flow cytometry, and moreover revealed the chromosome-arm locations of the HOSUT transgene in the HOSUT lines.

Re-assessment of biolistic transient expression: An efficient and robust method for protein localization studies in seedling-lethal mutant and juvenile plants

Knowledge on the subcellular localization of target proteins in a plant mutant background is important for revealing the function of the genes investigated. However, in Arabidopsis and rice, mutant lethality is one major barrier to such studies. Here we describe an optimized bombardment-mediated transient expression approach for studying subcellular protein localization in Arabidopsis seedling of lethal mutants. The whole experiment comprises four stages: cultivation and preparation of plants, coating gold particles with plasmid DNA, delivery of DNA into plants via bombardment, plant incubation and gene expression analysis which include localization and dynamics, co-localization comparison with reporter proteins and functional analysis. The entire process takes about 3-10 days from plant cultivation to protein detection. It has a high efficiency and the results are reproducible. Additionally, this protocol is applicable for the transient expression of chimeric fluorescent fusion proteins in juvenile rice seedlings and leaf sheaths, saving time dramatically in comparison of generating transgenic rice plant.

Biolistic Transformation of Wheat

The wheat genome encodes some 100,000 genes. To understand how the expression of these genes is regulated it will be necessary to carry out many genetic transformation experiments. Robust protocols that allow scientists to transform a wide range of wheat genotypes are therefore required. In this chapter, we describe a protocol for biolistic transformation of wheat that uses immature embryos and small quantities of DNA cassettes. An original method for DNA cassette purification is also described. This protocol can be used to transform a wide range of wheat genotypes and other related species.

Developing transgenic wheat to encounter rusts and powdery mildew by overexpressing barley chi26 gene for fungal resistance

BACKGROUND

The main aim of this study was to improve fungal resistance in bread wheat via transgenesis. Transgenic wheat plants harboring barley chitinase (chi26) gene, driven by maize ubi promoter, were obtained using biolistic bombardment, whereas the herbicide resistance gene, bar, driven by the CaMV 35S promoter was used as a selectable marker.

RESULTS

Molecular analysis confirmed the integration, copy number, and the level of expression of the chi26 gene in four independent transgenic events. Chitinase enzyme activity was detected using a standard enzymatic assay. The expression levels of chi26 gene in the different transgenic lines, compared to their respective controls, were determined using qRT-PCR. The transgene was silenced in some transgenic families across generations. Gene silencing in the present study seemed to be random and irreversible. The homozygous transgenic plants of T4, T5, T6, T8, and T9 generations were tested in the field for five growing seasons to evaluate their resistance against rusts and powdery mildew. The results indicated high chitinase activity at T0 and high transgene expression levels in few transgenic families. This resulted in high resistance against wheat rusts and powdery mildew under field conditions. It was indicated by proximate and chemical analyses that one of the transgenic families and the non-transgenic line were substantially equivalent.

CONCLUSION

Transgenic wheat with barley chi26 was found to be resistant even after five generations under artificial fungal infection conditions. One transgenic line was proved to be substantially equivalent as compared to the non-transgenic control.

A super twin T-DNA vector that allows independent gene expression during Agrobacterium-mediated transformation

In this study, we designed and constructed a super twin T-DNA vector (pTRIDT313-g) containing two independent T-DNA cassettes-one for the selection gene Hyg and the other for the target gene Gus-to produce marker-free transgenic lines. The resulting vector was transformed into tobacco, and polymerase chain reaction (PCR) analysis showed four types of gene combinations in the T1 and T2 generations: Gus only, Hyg only, Gus+Hyg, and untransformed lines. The intermediate region from the T-DNA of the right border of Hyg to the left border of Gus in the Hyg and Gus lines was not amplified. Genome walking confirmed that the Hyg and Gus T-DNA cassettes were independently inserted in different regions of the tobacco genome. Thus, the two T-DNA cassettes were integrated randomly as independent loci into the tobacco genome. The results of reverse transcription-PCR indicated that Hyg could normally be expressed in the roots, stems, and leaves of transgenic lines, and the resistance test showed that all Hyg transgenic lines could grow in the presence of 50mg/L hygromycin. All Gus transgenic lines showed obvious blue coloration in enzyme activity tests, indicating that the Gus gene could be normally expressed in all the lines. Therefore, the super twin T-DNA vector (pTRIDT313-g) exhibits independent integration, heredity, and normal gene function from two T-DNA cassettes. This vector could be a useful and valuable tool in the production of marker-free transgenic lines.

Physiological and comparative proteomic analysis reveals different drought responses in roots and leaves of drought-tolerant wild wheat (Triticum boeoticum)

To determine the proteomic-level responses of drought tolerant wild wheat (Triticum boeoticum), physiological and comparative proteomic analyses were conducted using the roots and the leaves of control and short term drought-stressed plants. Drought stress was imposed by transferring hydroponically grown seedlings at the 3-leaf stage into 1/2 Hoagland solution containing 20% PEG-6000 for 48 h. Root and leaf samples were separately collected at 0 (control), 24, and 48 h of drought treatment for analysis. Physiological analysis indicated that abscisic acid (ABA) level was greatly increased in the drought-treated plants, but the increase was greater and more rapid in the leaves than in the roots. The net photosynthetic rate of the wild wheat leaves was significantly decreased under short-term drought stress. The deleterious effects of drought on the studied traits mainly targeted photosynthesis. Comparative proteomic analysis identified 98 and 85 differently changed protein spots (DEPs) (corresponding to 87 and 80 unique proteins, respectively) in the leaves and the roots, respectively, with only 6 mutual unique proteins in the both organs. An impressive 86% of the DEPs were implicated in detoxification and defense, carbon metabolism, amino acid and nitrogen metabolism, proteins metabolism, chaperones, transcription and translation, photosynthesis, nucleotide metabolism, and signal transduction. Further analysis revealed some mutual and tissue-specific responses to short-term drought in the leaves and the roots. The differences of drought-response between the roots and the leaves mainly included that signal sensing and transduction-associated proteins were greatly up-regulated in the roots. Photosynthesis and carbon fixation ability were decreased in the leaves. Glycolysis was down-regulated but PPP pathway enhanced in the roots, resulting in occurrence of complex changes in energy metabolism and establishment of a new homeostasis. Protein metabolism was down-regulated in the roots, but enhanced in the leaves. These results will contribute to the existing knowledge on the complexity of root and leaf protein changes that occur in response to drought, and also provide a framework for further functional studies on the identified proteins.

Analysis of the APX, PGD1 and R1G1B constitutive gene promoters in various organs over three homozygous generations of transgenic rice plants

We have previously characterized the constitutively active promoters of the APX, PGD1 and R1G1B genes in rice (Park et al. 2010 in J Exp Bot 61:2459-2467). To have potential crop biotechnology applications, gene promoters must be stably active over many generations. In our current study, we report our further detailed analysis of the APX, PGD1 and R1G1B gene promoters in various organs and tissues of transgenic rice plants for three (T₃₋₅) homozygous generations. The copy numbers in 37 transgenic lines that harbor promoter:gfp constructs were determined and promoter activities were measured by real-time qPCR. Analysis of the 37 lines revealed that 15 contained a single copy of one of the three promoter:gfp chimeric constructs. The promoter activity levels were generally higher in multi-copy lines, whereas variations in these levels over the T₃₋₅ generations studied were observed to be smaller in single-copy than in multi-copy lines. The three promoters were further found to be highly active in the whole plant body at both the vegetative and reproductive stages of plant growth, with the exception of the APX in the ovary and R1G1B in the pistil and filaments where zero or very low levels of activity were detected. Of note, the spatial activities of the PGD1 promoter were found to be strikingly similar to those of the ZmUbi1, a widely used constitutive promoter. Our comparison of promoter activities between T₃, T₄ and T₅ plants revealed that the APX, PGD1 and R1G1B promoters maintained their activities at comparable levels in leaves and roots over three homozygous generations and are therefore potentially viable alternative promoters for crop biotechnology applications.

Expression of rice thaumatin-like protein gene in transgenic banana plants enhances resistance to fusarium wilt

The possibility of controlling Fusarium wilt--caused by Fusarium oxysporum sp. cubensec (race 4)--was investigated by genetic engineering of banana plants for constitutive expression of rice thaumatin-like protein (tlp) gene. Transgene was introduced to cauliflower-like bodies' cluster, induced from meristemic parts of male inflorescences, using particle bombardment with plasmid carrying a rice tlp gene driving by the CaMV 35S promoter. Hygromycin B was used as the selection reagent. The presence and integration of rice tlp gene in genomic DNA confirmed by PCR and Southern blot analyses. RT-PCR revealed the expression of transgene in leaf and root tissues in transformants. Bioassay of transgenic banana plants challenged with Fusarium wilt pathogen showed that expression of TLP enhanced resistance to F. oxysporum sp. cubensec (race 4) compared to control plants.

Transgenic Pm3b wheat lines show resistance to powdery mildew in the field

Plant resistance (R) genes are highly effective in protecting plants against diseases, but pathogens can overcome such genes relatively easily by adaptation. Consequently, in many cases R genes do not confer durable resistance in agricultural environments. One possible strategy to make the use of R genes more sustainable depends on the modification of R genes followed by transformation. To test a possible transgenic use of R genes, we overexpressed in wheat the Pm3b resistance gene against powdery mildew under control of the maize ubiquitin promoter. Four independent transgenic lines were tested in the greenhouse and the field during 3 years. The four lines showed a five- to 600-fold transgene overexpression compared with the expression of the endogenous Pm3b gene in the landrace 'Chul'. Powdery mildew resistance was significantly improved in all lines in the greenhouse and the field, both with naturally occurring infection or after artificial inoculation. Under controlled environmental conditions, the line with the strongest overexpression of the Pm3b gene showed a dramatic increase in resistance to powdery mildew isolates that are virulent on the endogenous Pm3b. Under a variety of field conditions, but never in the greenhouse, three of the four transgenic lines showed pleiotropic effects on spike and leaf morphology. The highest overexpressing line had the strongest side effects, suggesting a correlation between expression level and phenotypic changes. These results demonstrate that the successful transgenic use of R genes critically depends on achieving an optimal level of their expression, possibly in a tissue-specific way.

Stability and inheritance of endosperm-specific expression of two transgenes in progeny from crossing independently transformed barley plants

To study stability and inheritance of two different transgenes in barley, we crossed a homozygous T(8) plant, having uidA (or gus) driven by the barley endosperm-specific B(1)-hordein promoter (localized in the near centromeric region of chromosome 7H) with a second homozygous T(4) plant, having sgfp(S65T) driven by the barley endosperm-specific D-hordein promoter (localized on the subtelomeric region of chromosome 2H). Both lines stably expressed the two transgenes in the generations prior to the cross. Three independently crossed F(1) progeny were analyzed by PCR for both uidA and sgfp(S65T) in each plant and functional expression of GUS and GFP in F(2) seeds followed a 3:1 Mendelian segregation ratio and transgenes were localized by FISH to the same location as in the parental plants. FISH was used to screen F(2) plants for homozygosity of both transgenes; four homozygous plants were identified from the two crossed lines tested. FISH results showing presence of transgenes were consistent with segregation ratios of expression of both transgenes, indicating that the two transgenes were expressed without transgene silencing in homozygous progeny advanced to the F(3) and F(4) generations. Thus, even after crossing independently transformed, homozygous parental plants containing a single, stably expressed transgene, progeny were obtained that continued to express multiple transgenes through generation advance. Such stability of transgenes, following outcrossing, is an important attribute for trait modification and for gene flow studies.

Molecular genetic improvement of cereals: transgenic wheat (Triticum aestivum L.)

Only modest progress has been made in the molecular genetic improvement of wheat following the production of the first transgenic plants in 1992, made possible by the development of efficient, long-term regenerable embryogenic cultures derived from immature embryos and use of the biolistics method for the direct delivery of DNA into regenerable cells. Transgenic lines expressing genes that confer resistance to environmentally friendly non-selective herbicides, and pests and pathogens have been produced, in addition to lines with improved bread-making and nutritional qualities; some of these are ready for commercial production. Reduction of losses caused by weeds, pests and pathogens in such plants not only indirectly increases available arable land and fresh water supplies, but also conserves energy and natural resources. Nevertheless, the work carried out thus far can be considered only the beginning, as many difficult tasks lie ahead and much remains to be done. The challenge now is to produce higher-yielding varieties that are more nutritious, and are resistant or tolerant to a wide variety of biotic as well as abiotic stresses (especially drought, salinity, heavy metal toxicity) that currently cause substantial losses in productivity. How well we will meet this challenge for wheat, and indeed for other cereal and non-cereal crops, will depend largely on establishing collaborative partnerships between breeders, molecular biologists, biotechnologists and industry, and on how effectively they make use of the knowledge and insights gained from basic studies in plant biology and genetics, the sequencing of plant/cereal genomes, the discovery of synteny in cereals, and the availability of DNA-based markers and increasingly detailed chromosomal maps.

Co-bombardment, integration and expression of rice chitinase and thaumatin-like protein genes in barley (Hordeum vulgare cv. Conlon)

Pathogenesis-related (PR) proteins associated with degradation of structural components of pathogenic filamentous fungi were overexpressed in the two-rowed malting barley (Hordeum vulgare L.) cultivar Conlon. Transgenes were introduced by co-bombardment with two plasmids, one carrying a rice (Oryza sativa L.) chitinase gene (chi11) and another carrying a rice thaumatin-like protein gene (tlp). Each gene was under the control of the maize ubiquitin (Ubi1) promoter. Fifty-eight primary transformants from three independent transformation events were regenerated. T(1) plants with high rice chi11 and tlp protein expression levels were advanced to identify T(2) homozygotes by herbicide spray and subjected to further molecular analyses. T(3) progeny from one event (E2) had stable integration and expression of the rice chi11 and tlp while those from the other events (E1 and E3) showed stable integration only of tlp. The successful production of these lines overexpressing the antifungal chi and tlp proteins provides materials to test the effects of these genes on a variety of fungal diseases that attack barley and to serve as potential additional sources of disease resistance.

Arabidopsis VIRE2 INTERACTING PROTEIN2 is required for Agrobacterium T-DNA integration in plants

Agrobacterium tumefaciens-mediated genetic transformation is an efficient tool for genetic engineering of plants. VirE2 is a single-stranded DNA binding Agrobacterium protein that is transported into the plant cell and presumably protects the T-DNA from degradation. Using a yeast two-hybrid system, we identified Arabidopsis thaliana VIRE2-INTERACTING PROTEIN2 (VIP2) with a NOT domain that is conserved in both plants and animals. Furthermore, we provide evidence supporting VIP2 interaction with VIP1, a basic domain/leucine zipper motif-containing protein required for nuclear import and integration of T-DNA. Virus-induced gene silencing of VIP2 in Nicotiana benthamiana and characterization of the Arabidopsis vip2 mutant (At vip2) demonstrate that VIP2 is required for Agrobacterium-mediated stable transformation but not for transient transformation. Assays based upon a promoter-trap vector and quantification of T-DNA integration further confirmed VIP2 involvement in T-DNA integration. Interestingly, VIP2 transcripts were induced to a greater extent over prolonged periods after infection with a T-DNA transfer-competent Agrobacterium strain compared with the transfer-deficient Agrobacterium strain. Transcriptome analyses of At vip2 suggest that VIP2 is likely a transcriptional regulator, and the recalcitrancy to transformation in At vip2 is probably due to the combination of muted gene expression response upon Agrobacterium infection and repression of histone genes resulting in decreased T-DNA integration events.

Changes of some anti-oxidative physiological indices under soil water deficits among 10 wheat (Triticum aestivum L.) genotypes at tillering stage

Drought is one of the major ecological factors limiting crop production and food quality globally, especially in the arid and semi-arid areas of the world. Wheat is the staple food for more than 35% of world population and wheat cultivation is mainly restricted to such zones with scarcity of water, so wheat anti-drought physiology study is of importance to wheat production, food safety and quality and biotechnological breeding for the sake of coping with abiotic and biotic conditions. The current study is to investigate changes of anti-oxidative physiological indices of 10 wheat genotypes at tillering stage. The main results and conclusion of tillering stage in terms of activities of POD, SOD, CAT and MDA content as followed: (1) 10 wheat genotypes can be generally grouped into three kinds (A-C, respectively) according to their changing trend of the measured indices; (2) A group performed better drought resistance under the condition of treatment level 1 (appropriate level), whose activities of anti-oxidative enzymes (POD, SOD, CAT) were higher and MDA lower; (3) B group exhibited stronger anti-drought under treatment level 2 (light-stress level), whose activities of anti-oxidative enzymes were higher and MDA lower; (4) C group expressed anti-drought to some extent under treatment level 3 (serious-stress), whose activities of anti-oxidative enzymes were stronger, MDA lower; (5) these results demonstrated that different wheat genotypes have different physiological mechanisms to adapt themselves to changing drought stress, whose molecular basis is discrete gene expression profiling (transcriptom). The study in this respect is the key to wheat anti-drought and biological-saving water in worldwide arid and semi-arid areas; (6) POD, SOD, and CAT activities and MDA content of different wheat genotypes had quite different changing trend at different stages and under different soil water stress conditions, which was linked with their origin of cultivation and individual soil water threshold, which will provide better reference to selecting proper plant species for eco-environmental construction and crops for sustainable agriculture in arid and semi-arid areas.

Relationship between water use efficiency (WUE) and production of different wheat genotypes at soil water deficit

Through 2-year field experiments, 7 wheat genotypes were better in their field yield. These 7 wheat genotypes and other 3 wheat species, which are being popularized on a large scale in different locations of China, were selected as experimental materials for the sake of measuring their difference in WUE and production and comparing their relationship at soil water deficits, future more, providing better drought resistance lines and theoretical guide for wheat production and practices and exploring anti-drought physiological mechanisms of different wheat genotypes. Under the condition of 3 soil-water-stress treatments (75% field capacity (FC), 55% FC, 45% FC, named level 1, level 2 and level 3, respectively), pot experiments for them were conducted and the related data were collected from their life circle. The main results were as followed: (1) according to the selected soil stress levels, water use efficiency (WUE) of 10 different wheat genotypes was divided into two groups (A and B); group A included genotypes 2, 3, 4, 5, 6, 7, 8, whose WUE decreased basically from level 1 to level 3 and reached individual peak of WUE at level 1; Group 2 included genotypes 1, 9, 10, whose WUE reached their individual peak at level 2; (2) based on total water consumption through all life circle, genotypes 1, 4, 8, 9 had lower water consumption (TWC) at level 1, genotypes 2, 3, 5, 6, 7 lower TWC at level 2, genotype 10 lower TWC at level 3; (3) at level 1, genotypes 2, 3, 4, 5, 6, 7, 8 had higher grain weight of single spike (GWSS), genotypes 1, 9, 10 better GWSS at level 2, which was in good line with individual WUE of different wheat genotypes; (4) by analyzing the indexes related to examining cultivars, it was found that genotypes 1, 2, 3, 4, 5, 6, 9, 10 had longer plant length (PL), spike length (SL), bigger grain number (GN) except genotypes 7 and 8 at level 1, RL was in better line with genotypes 1, 2, 3, 8, 9, 10, but not in the other genotypes at level 1.

Investigation on the relationship of proline with wheat anti-drought under soil water deficits

Proline (content) is closely with plant anti-drought, especially under soil water deficits. Many reports from crops and other plants have proved this. Wheat is the second important crop on the globe, whose research in this aspect of importance for food quality, safety, and yield in field. The related difference in physiological indicators and proline content for different soil water treatments among wheat with different genotypes is not clear, which has limited deep study of wheat anti-drought molecular biology and related anti-drought biotechnological breeding. Our current study was focused on the physiological relationship of proline and different genotype wheat anti-drought under soil water deficits. Main results showed that different wheat genotype had different soil water stress threshold. Pro content had closed relationship with soil water stress threshold and wheat anti-drought. Developmental course also impacted Pro content for different wheat genotypes.

Expression of the lipid transfer protein Ace-AMP1 in transgenic wheat enhances antifungal activity and defense responses

To enhance fungal disease resistance, wheat plants (cv. Bobwhite) were engineered to constitutively express the potent antimicrobial protein Ace-AMP1 from Allium cepa, driven by a maize ubiquitin promoter along with its first intron. The bar gene was used for selection of putative transformants on medium containing phosphinothricin (PPT). Transgene inheritance, integration and stability of expression were confirmed over two generations by PCR, Southern, northern and western blot analyses, respectively. The levels of Ace-AMP1 in different transgenic lines correlated with the transcript levels of the transgene. Up to 50% increase in resistance to Blumeria graminis f. sp. tritici was detected in detached leaf assays. In ears of transgenic wheat inoculated with Neovossia indica, Ace-AMP1 intensified expression of defense-related genes. Elevated levels of salicylic acid and of transcripts of phenylalanine ammonia lyase (PAL), glucanase (PR2) and chitinase (PR3) in the transgenic plants indicated manifestation of systemic acquired resistance (SAR).

Understanding molecular mechanism of higher plant plasticity under abiotic stress

Higher plants play the most important role in keeping a stable environment on the earth, which regulate global circumstances in many ways in terms of different levels (molecular, individual, community, and so on), but the nature of the mechanism is gene expression and control temporally and spatially at the molecular level. In persistently changing environment, there are many adverse stress conditions such as cold, drought, salinity and UV-B (280-320 mm), which influence plant growth and crop production greatly. Plants differ from animals in many aspects, but the important may be that plants are more easily influenced by environment than animals. Plants have a series of fine mechanisms for responding to environmental changes, which has been established during their long-period evolution and artificial domestication. These mechanisms are involved in many aspects of anatomy, physiology, biochemistry, genetics, development, evolution and molecular biology, in which the adaptive machinery related to molecular biology is the most important. The elucidation of it will extremely and purposefully promote the sustainable utilization of plant resources and make the best use of its current potential under different scales. This molecular mechanism at least include environmental signal recognition (input), signal transduction (many cascade biochemical reactions are involved in this process), signal output, signal responses and phenotype realization, which is a multi-dimensional network system and contain many levels of gene expression and regulation. We will focus on the molecular adaptive machinery of higher plant plasticity under abiotic stresses.

Comparative field performance over 3 years and two sites of transgenic wheat lines expressing HMW subunit transgenes

A series of transgenic wheat lines expressing additional high molecular weight (HMW) subunit genes and the corresponding control lines were grown in replicate field trials at two UK sites (Rothamsted Research, approximately 50 km north of London and Long Ashton, near Bristol) over 3 years (1998, 1999, 2000), with successive generations of the transgenic lines (T3, T4, T5) being planted. Four plots from each site were used to determine grain dry weight, grain nitrogen, dough strength (measured as peak resistance by Mixograph analysis) and the expression levels of the endogenous and "added" subunits. Detailed statistical analyses showed that the transgenic and non-transgenic lines did not differ in terms of stability of HMW subunit gene expression or in stability of grain nitrogen, dry weight or dough strength, either between the 3 years or between sites and plots. These results indicate that the transgenic and control lines can be regarded as substantially equivalent in terms of stability of gene expression between generations and environments.

Osmotic regulation of 10 wheat (Triticum aestivum L.) genotypes at soil water deficits

Drought is a worldwide problem, seriously influencing plant (crop) productivity. Wheat is a stable food for 35% of the world population, moreover about 60% of land area on the globe belongs to arid and semi-arid zone. Wheat drought resistance is a multi-gene-controlling quantitative character and wheat final production in field is realized mainly by physiological regulation under the condition of multi-environmental factor interaction. Exploring drought resistance physiological mechanisms for different wheat genotypes is of importance to finding new drought resistance gene resources and conventional breeding and the basis for wheat drought resistance biotechnological breeding and platform. Osmotic adjustment regulation is the main component for physiological machinery of wheat drought resistance. By pot-cultivating experiments, investigation of osmotic adjustment comparison for 10 wheat genotypes at soil water deficits (75% FC, 55% FC, 45% FC, respectively), was conducted. The main results were as followed: (1) K(+) content in 10 wheat genotypes at three levels of soil water stress and at the same soil water deficit was very different. Five of these 10 wheat genotypes had higher K K(+) content under the condition of 75% FC. (2) Five of these 10 wheat genotypes possessed greater soluble sugar content at 55% FC soil water level. (3) Proline (Pro) content in five wheat genotypes was higher at 75% FC. (4) Five of these 10 wheat genotypes had lower malondialdehyde (MDA) content at 45% FC at seedling stage. Osmotic adjustment of wheat different genotypes was discussed in terms of different content of osmotic solutes.

Changes of anti-oxidative enzymes and MDA content under soil water deficits among 10 wheat (Triticum aestivum L.) genotypes at maturation stage

Drought is a world-spread problem seriously influencing grain production and quality, the loss of which is the total for other natural disasters, with increasing global climate change making the situation more serious. Wheat is the staple food for more than 35% of world population, so wheat anti-drought physiology study is of importance to wheat production and biological breeding for the sake of coping with abiotic and biotic conditions. Much research is involved in this hot topic, but the pace of progress is not so large because of drought resistance being a multiple-gene-control quantitative character and wheat genome being larger (16,000Mb). On the other hand, stress adaptive mechanisms are quite different, with stress degree, time course, materials, soil quality status and experimental plots, thus increasing the complexity of the issue in question. Additionally, a little study is related to the whole life circle of wheat, which cannot provide a comprehensive understanding of its anti-drought machinery. We selected 10 kinds of wheat genotypes as materials, which have potential to be applied in practice, and measured change of relative physiological indices through wheat whole growing-developmental circle (i.e. seedling, tillering and maturing). Here, we reported the anti-oxidative results of maturation stage (the results of seedling and tillering stage have been published) in terms of activities of POD, SOD, CAT and MDA content as follows: (1) 10 wheat genotypes can be grouped into three kinds (A-C, respectively) according to their changing trend of the measured indices; (2) A group performed better resistance drought under the condition of treatment level 1 (appropriate level), whose activities of anti-oxidative enzymes (POD, SOD, CAT) were higher and MDA lower; (3) B group exhibited stronger anti-drought under treatment level 2 (light-stress level), whose activities of anti-oxidative enzymes were higher and MDA lower; (4) C group expressed anti-drought to some extent under treatment level 3 (serious-stress level), whose activities of anti-oxidative enzymes were stronger, MDA lower; (5) these results demonstrated that different wheat genotypes have different physiological mechanisms to adapt themselves to changing drought stress, whose molecular basis is discrete gene expression profiling (transcriptom); (6) our results also showed that the concept and method accepted and adopted by most researchers [T.C. Hsiao, Plant response to water stress, Ann. Rev. Plant Physiol. 24 (1973) 519-570], that 75% FC is a proper supply for higher plants, was doubted, because this level could not reflect the true suitable level of different wheat genotypes. The study in this respect is the key to wheat anti-drought and biological-saving water agriculture; (7) our research can provide insights into physiological mechanisms of crop anti-drought and direct practical materials for wheat anti-drought breeding; (8) the physiological study of wheat is more urgent up-to-date and molecular aspects are needed, but cannot substitute this important part. The combination of both is an important strategy and a key and (9) POD, SOD and CAT activities and MDA content of different wheat genotypes had quite different changing trend at different stages and under different soil water stress conditions, which was linked with their origin of cultivation and individual soil water threshold.

Investigation on dynamic changes of photosynthetic characteristics of 10 wheat (Triticum aestivum L.) genotypes during two vegetative-growth stages at water deficits

Drought is a worldwide problem, seriously influencing plant (crop) productivity. Wheat is a stable food for 35% of the world population, and moreover, about 60% of land area on the globe belongs to arid and semiarid zone. Wheat drought resistance is a multi-gene controlling quantitative character and wheat final production in field is realized mainly by physiological regulation under the condition of multi-environmental factor interaction. Exploring drought resistance physiological mechanisms for different wheat genotypes is of importance to finding new drought resistance gene resources and conventional breeding, and the basis for wheat drought resistance biotechnological breeding and platform. Photosynthesis is the main component for physiological machinery of wheat assimilates conversion and wheat production. Investigation on photosynthetic characteristics of different wheat genotypes at soil water deficits also has other implications for refine physiological regulation of photosynthesis in fields and field management of crops in arid and semiarid areas. By pot-cultivating experiments, investigation of photosynthesis for 10 wheat genotypes at seedling stage and tillering stage at soil water deficits (75%FC, 55%FC and 45%FC, respectively) was conducted. The main results were as followed: developmental stages influenced wheat photosynthesis greatly and tillering stage played more roles; there were significant difference in the main photosynthetic parameters, photosynthesis rate (Photo), stomatal conductance (Cond) and transpiration rate (Tr), among 10 wheat genotypes; general photosynthesis and drought resistance in different wheat genotypes was related much to their domesticated origin soil water environment and selected generations and there was a photosynthetic threshold effect in terms of different wheat genotypes at soil water deficits.

Changes of anti-oxidative enzymes and membrane peroxidation for soil water deficits among 10 wheat genotypes at seedling stage

Drought is one of the major factors limiting crop production globally, with increasing global climate change making the situation more serious. Wheat is the staple food for more than 35% of world population, so wheat anti-drought physiology study is of importance to wheat production and biological breeding for the sake of coping with abiotic and biotic conditions. Much research is involved in this hot topic, but the pace of progress is not so large because of drought resistance being a multiple-gene-control quantitative character and wheat genome being larger (16,000 Mb). On the other hand, stress adaptive mechanisms are quite different, with stress degree, time course, materials, and experimental plots, thus increasing the complexity of the issue in question. Additionally, a little study is related to the whole life circle of wheat, which cannot provide a comprehensive understanding of its anti-drought machinery. We selected 10 kinds of wheat genotypes as materials, which have potential to be applied in practice, and measured relative change of anti-oxidative enzymes and membrane peroxidation through wheat whole growth-developmental circle (i.e. seedling, tillering and maturing). Here, we firstly reported the results of seedling stage as follows: (1) 10 wheat genotypes can be grouped into three kinds (A-C, respectively) according to their changing trend of the measured indices; (2) A performed better resistance drought under the condition of treatment level 1 (appropriate level), whose activities of anti-oxidative enzymes (POD, SOD, CAT) were higher and MDA lower and chlorophyll a+b higher; (3) B exhibited stronger anti-drought under treatment level 2 (light stress level), whose activities of anti-oxidative enzymes were higher, MDA lower and chlorophyll higher; (4) C expressed anti-drought to some extent under treatment level 3 (serious stress), whose activities of anti-oxidative enzymes were stronger, MDA lower and chlorophyll higher; (5) these results demonstrated that different wheat genotypes have different physiological mechanisms to adapt themselves to changing drought stress, whose molecular basis is discrete gene expression profiling (transcriptom); (6) our results also showed that the concept accepted by most researchers, 70-75% QF is a proper supply for plants, was doubted, because this level could not reflect the true suitable level of wheat. The study in this respect is the key to wheat anti-drought and biological saving-water; (7) our research can provide insights into physiological mechanisms of crop anti-drought and direct practical materials for wheat anti-drought breeding.

Dynamic changes of anti-oxidative enzymes of 10 wheat genotypes at soil water deficits

Drought is a world-spread problem seriously influencing crop production and quality, the loss of which is the total for other natural disasters, with increasing global climate change making the situation more serious. Wheat is the staple food for more than 35% of world population, so wheat anti-drought physiology study is of importance to wheat production and biological breeding for the sake of coping with abiotic and biotic conditions. Much research is involved in this hot topic, but the pace of progress is not so large because of drought resistance being a multiple-gene-control quantitative character and wheat genome being larger (16,000 Mb). On the other hand, stress adaptive mechanisms are quite different, with stress degree, different growth and developmental stages, time course, materials and experimental plots, thus increasing the complexity of the issue in question. Additionally, a little study is related to the whole life circle of wheat, which cannot provide a comprehensive understanding of its anti-drought machinery. We selected 10 kinds of wheat genotypes as materials, which have potential to be applied in practice, and measured change of relative physiological indices through wheat whole growing developmental circle (i.e. seedling, tillage and maturing). Here, we reported the dynamic anti-oxidative results of whole stage (i.e. seedling, tillage and maturing) in terms of activities of POD, SOD, CAT of 10 wheat genotypes as follows: (1) 10 wheat genotypes can be grouped into three kinds (A, B and C, respectively) according to their changing trend of the measured indices; (2) A group performed better resistance drought under the condition of treatment level 1, whose activities of anti-oxidative enzymes (POD, SOD, CAT) were higher; (3) B group exhibited stronger anti-drought under treatment level 2, whose activities of anti-oxidative enzymes were higher; (4) C group expressed anti-drought to some extent under treatment level 3, whose activities of anti-oxidative enzymes were stronger, MDA lower; (5) these results demonstrated that different wheat genotypes have different physiological mechanisms to adapt themselves to changing drought stress, whose molecular basis is discrete gene expression profiling (transcriptom); (6) our results also showed that the concept and method accepted and adopted by most researchers--that 75% FC is a proper supply for higher plants--was doubted because this level could not reflect the true suitable level of different wheat genotypes; (7) our research can provide insights into physiological mechanisms of crop anti-drought and direct practical materials for wheat anti-drought breeding; (8) POD, SOD and CAT activities of different wheat genotypes had quite different changing trend at different stages and under different soil water stress conditions, which was linked with their origin of cultivation and individual soil water stress threshold; (9) our primary results also firstly displayed that the changing trend for wheat adapting to environmental stress during life circle was an S-shaped curve, which is, by chance, consistent with Plant Growth Grand Periodicity Curve.

Development of a lesion-mimic phenotype in a transgenic wheat line overexpressing genes for pathogenesis-related (PR) proteins is dependent on salicylic acid concentration

In the course of coexpressing genes for pathogenesis-related (PR) proteins for a class IV chitinase and an acidic glucanase in transgenic wheat plants, we regenerated a wheat line that developed necrotic lesions containing dead cells in the T2 and subsequent generations. Lesion spots were detected at the booting stage (5- to 6-week-old plants) in lines homozygous for the transgene loci. In contrast, lesions were not observed in hemizygous transgenic lines or lines silenced for transgene expression, indicating a requirement for high levels of transgene expression for the development of the lesioned phenotype. Lesion development was associated with the accumulation of host-encoded PR proteins, e.g., chitinases, beta-1,3-glucanases, thaumatin-like protein, and production of reactive oxygen intermediates. F1 progeny of a cross between the lesion-plus transgenic line and wild-type nontransgenic plants produced progeny with a normal phenotype, while the F2 progenies segregated for the lesion phenotype. Salicylic acid (SA) levels in plants with the lesion-plus phenotype were found to be several times higher than controls and nearly double the levels in hemizygous transgenic plants that lack lesions. SA application activated lesion development in excised leaf pieces of these hemizygous transgenic plants. Similar activation of lesion development in control plants occurred only when high concentrations of SA were applied for prolonged periods. Transcripts for phenylalanine-ammonia lyase, which provides precursors of SA, were elevated in homozygous transgenic plants. Our data suggest that transgene-induced lesion-mimic phenotype correlates with enhanced SA biosynthesis.