Growth and Solute Composition in Two Wheat Species Experiencing Combined Influence of Stress Conditions1

The effects of environmental stress combinations on the soluble metabolites were investigated in several cultivars of Triticum aestivum and T. durum. The seedlings grown at optimum (24/16°C), low (5/–5°C) (LT), and high (40/30°C) (HT) day/night temperature conditions were exposed to waterlogging, drought, and salinity (0.7% NaCl, w/w) stresses for six days. Root and shoot fresh weight significantly decreased under waterlogging, drought and salt stresses. Fresh weight was most reduced at severe drought + HT combinations. The lowest relative water content was found under drought stress + HT combination. Soluble carbohydrate (SC) contents increased under LT conditions, but decreased under HT conditions. Under HT + salt combinations, T. aestivum genotypes showed higher SC content thanT. durum genotypes. Proline content significantly increased in the case of water deficit and salt stress. Under drought and salt stresses, T. aestivum genotypes had lower proline contents than T. durum genotypes. These results indicate that biochemical responses to drought, waterlogging, and salt stresses were significantly changed in wheat seedlings under LT and HT conditions.     

Overexpression of the maize Teosinte Branched1 gene in wheat suppresses tiller development

The number of viable shoots influences the overall architecture and productivity of wheat (Triticum aestivum L.). The development of lateral branches, or tillers, largely determines the resultant canopy. Tillers develop from the outgrowth of axillary buds, which form in leaf axils at the crown of the plant. Tiller number can be reduced if axillary buds are not formed or if the outgrowth of these buds is restricted. The teosinte branched1 (tb1) gene in maize, and homologs in rice and Arabidopsis, genetically regulate vegetative branching. In maize, increased expression of the tb1 gene restricts the outgrowth of axillary buds into lateral branches. In this study, the maize tb1 gene was introduced through transformation into the wheat cultivar "Bobwhite" to determine the effect of tb1 overexpression on wheat shoot architecture. Examination of multiple generations of plants reveals that tb1 overexpression in wheat results in reduced tiller and spike number. In addition, the number of spikelets on the spike and leaf number were significantly greater in tb1-expressing plants, and the height of these plants was also reduced. These data reveal that the function of the tb1 gene and genetic regulation of lateral branching via the tb1 mode of action is conserved between wheat, rice, maize and Arabidopsis. Thus, the tb1 gene can be used to alter plant architecture in agriculturally important crops like wheat.     

Comparison of effects of salt and alkali stresses on the growth and photosynthesis of wheat

The seedlings of wheat were treated by salt-stress (SS, molar ratio of NaCl: Na₂SO₄ = 1: 1) and alkali-stress (AS, molar ratio of NaHCO₃: Na₂CO₃ = 1: 1). Relative growth rate (RGR), leaf area, and water content decreased with increasing salinity, and the extents of the reduction under AS were greater than those under SS. The contents of photosynthetic pigments did not decrease under SS, but increased at low salinity. On the contrary, the contents of photosynthetic pigments decreased sharply under AS with increasing salinity. Under SS, the changes of net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were similar and all varied in a single-peak curve with increasing salinity, and they were lower than those of control only at salinity over 150 mM. Under AS, P _N, g _s, and E decreased sharply with rising salinity. The decrease of g _s might cause the obvious decreases of E and intercellular CO₂ concentration, and the increase of water use efficiency under both stresses. The Na⁺ content and Na⁺/K⁺ ratio in shoot increased and the K⁺ content in shoot decreased under both stresses, and the changing extents under AS were greater than those under SS. Thus SS and AS are two distinctive stresses with different characters; the destructive effects of AS on the growth and photosynthesis of wheat are more severe than those under SS. High pH is the key feature of the AS that is different from SS. The buffer capacity is essentially the measure of high pH action on plant. The deposition of mineral elements and the intracellular unbalance of Na⁺ and K⁺ caused by the high pH at AS might be the reason of the decrease of P _N and g _s and of the destruction of photosynthetic pigments.     

Genome organisation and retrotransposon driven molecular evolution of the endosperm Hardness (Ha) locus in Triticum aestivum cv Glenlea

Wheat endosperm texture is controlled primarily by a locus (Ha), which comprises Gsp-1, Pina and Pinb genes encoding the so-called grain softness protein, puroindoline-a and puroindoline-b, respectively. Pina and Pinb were detected only on the D-genome of hexaploid wheat and its diploid progenitors while Gsp-1 was on all three homoeologous loci. Hexaploid cultivar Glenlea has a hard phenotype due to a null Pina genotype (D-genome) but the sequence organization is not reported. This study aimed at understanding the evolution of homoeologous Ha loci. Sequencing of three BAC clones from cv Glenlea was performed and sequence analyses delimited the Ha loci which spanned 3,925, 5,330 and 31,607 bp in the A-, B- and D-genomes, respectively. A solo LTR of Angela retroelement, downstream to Gsp-A1 and a fragment of Sabrina retroelement, downstream of Gsp-B1, were discovered. We propose that the insertion of these elements into the intergenic regions have driven the deletions of genomic segments harbouring Pina and Pinb genes in the A- and B-genomes of hexaploid wheat. Similarly, fragments of Romani and Vagabond retroelements were identified between truncated Pina and Pinb genes, indicating their role in the deletion of Pina in Glenlea, leading to its hard texture. Structural differences of the Ha locus region of the A-genome between two hexaploid wheat varieties namely Glenlea and Renan (CR626929), suggested the presence of more than one tetraploid ancestor in the origin of hexaploid wheat.     

Hessian fly resistance genes <Emphasis Type="Italic">H16</Emphasis> and <Emphasis Type="Italic">H17</Emphasis> are mapped to a resistance gene cluster in the distal region of chromosome 1AS in wheat

Hessian fly [Mayetiola destructor (Say)] is one of the major insect pests of wheat (Triticum aestivum L.) worldwide. Hessian fly (Hf)-resistance genes H16 and H17 were reported to condition resistance to Hf biotype L that is prevalent in many wheat-growing areas of eastern USA, and both of them were previously assigned to wheat chromosome 5A by their linkage to H9. The objectives in this study were to (1) map H16 and H17 independent of their linkage with H9 and (2) identify DNA markers that co-segregate with H16 or H17, and that are useful for selection of these genes in segregating populations and to combine these genes with other Hf-resistance genes in wheat cultivars. Contrary to previously reported locations, H16 and H17 did not show linkage with the molecular markers on chromosome 5A. Instead, both of them are linked with the molecular markers on the short arm of chromosome 1A (1AS). The simple sequence repeat (SSR) marker Xpsp2999 and EST-derived SSR (eSSR) marker Xwem6b are two flanking markers that are linked to H16 at genetic distances of 3.7 and 5.5 cM, respectively. Similarly, H17 is located between markers Xpsp2999 and Xwem6b at genetic distances of 6.2 and 5.1 cM, respectively. Five other SSR and eSSR markers including Xcfa2153, Xbarc263, Xwem3a, Xwmc329, and Xwmc24 were also linked to H16 and H17 at close genetic distances. These closely linked molecular markers should be useful for pyramiding H16 and H17 with other Hessian fly resistance genes in a single wheat genotype. In addition, using Chinese Spring deletion line bin mapping we positioned all of the linked markers and the Hf-resistance genes (H16 and H17) to the distal 14% of chromosome 1AS, where Hf-resistance genes H9, H10, and H11 are located. Our results together with previous studies suggest that Hf-resistance genes H9, H10, H11, H16, and H17 along with the pathogen resistance genes Pm3 and Lr10 appear to occupy a resistance gene cluster in the distal region of chromosome 1AS in wheat. Contribution from Purdue Univ. Agric. Res. Programs Journal Article No. 2007-18105.     

Genomic targeting and mapping of tiller inhibition gene (<Emphasis Type="Italic">tin3</Emphasis>) of wheat using ESTs and synteny with rice

Changes in plant architecture have been central to the domestication of wild species. Tillering or the degree of branching determines shoot architecture and is a key component of grain yield and/or biomass. Previously, a tiller inhibition mutant with monoculm phenotype was isolated and the mutant gene (tin3) was mapped in the distal region of chromosome arm 3A^mL of Triticum monococcum. As a first step towards isolating a candidate gene for tin3, the gene was mapped in relation to physically mapped expressed sequence tags (ESTs) and sequence tag site (STS) markers developed based on synteny with rice. In addition, we investigated the relationship of the wheat region containing tin3 with the corresponding region in rice by comparative genomic analysis. Wheat ESTs that had been previously mapped to deletion bins provided a useful framework to identify closely related rice sequences and to establish the most likely syntenous region in rice for the wheat tin3 region. The tin3 gene was mapped to a 324-kb region spanned by two overlapping bacterial artificial chromosomes (BACs) of rice chromosome arm 1L. Wheat–rice synteny was exceptionally high at the tin3 region despite being located in the high-recombination, gene-rich region of wheat. Identification of tightly linked flanking EST and STS markers to the tin3 gene and its localization to highly syntenic rice BACs will assist in the future development of a high-resolution map and map-based cloning of the tin3 gene. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Wheat stem sawfly‐infested plants benefit from parasitism of the herbivorous larvae

1 Parasitoids Bracon cephi (Gahan) and Bracon lissogaster Muesebeck and their herbivorous host the wheat stem sawfly Cephus cinctus Norton, a pest of wheat Triticum aestivum, were investigated for yield in T. aestivum grown in the field. 2 Wheat stem sawfly‐infested stems had a higher yield potential than uninfested stems. However, final reproductive output was not significantly different between ears on infested stems that supported complete larval development compared with ears on uninfested stems. 3 Stems containing parasitized larvae and stems containing larvae that died before completing their development had a higher mean number of seeds and seed weight, when accounting for number of fertile spikelets of each ear, than either infested with live larvae and uninfested stems. 4 The results obtained suggest that larval feeding prevented infested stems from attaining their yield potential, and that the negative impact of the pest on wheat yield was reduced when late instar sawfly larvae were parasitized. Even though some feeding occurs before parasitism, this early damage has a comparatively low impact on yield. 5 This is the first study to show a yield benefit and enhanced plant fitness due to the wheat stem sawfly parasitoids B. cephi and B. lissogaster. This results from the maintenance of increased seed number and seed weight in the higher yielding stems that are preferentially infested by this pest.     

Identification of new T1BL.1RS translocation lines derived from wheat (Triticum aestivum L. cultivar “Xiaoyan No. 6”) and rye hybridization

Two new T1BL.1RS translocation lines, 48112 and 89121, derived from cross between common wheat (Triticum aestivum L.) cultivar “Xiaoyan No. 6” and rye (Secale cereale L.) cultivar “German White”, were developed and identified by using of molecular markers and cytogenetical methods, GISH and FISH. PCR results of primers NOR-R1 specific for rye and Glu-B3 for 1BS detected the presence of 1RS chromatin and absence of 1BS, and primer for gene 1Bx14 in 1BL indicated the existence of chromosome arm 1BL in the two lines. GISH and FISH methods confirmed the replacement of chromosome arm 1BS with 1RS. Further stripe rust resistant test and quality analysis demonstrated that the new 1BL.1RS translocation lines were higher resistant to mixed races of P. striiformis Westend and observed considerable better quality than other popularized T1BL.1RS cultivars in China. The two lines have been used in wheat breeding for high-yield potential and rust resistance.     

Fusarium graminearum gene deletion mutants map1 and tri5 reveal similarities and differences in the pathogenicity requirements to cause disease on Arabidopsis and wheat floral tissue

The Ascomycete pathogen Fusarium graminearum can infect all cereal species and lower grain yield, quality and safety. The fungus can also cause disease on Arabidopsis thaliana. In this study, the disease-causing ability of two F. graminearum mutants was analysed to further explore the parallels between the wheat (Triticum aestivum) and Arabidopsis floral pathosystems. Wild-type F. graminearum (strain PH-1) and two isogenic transformants lacking either the mitogen-activated protein kinase MAP1 gene or the trichodiene synthase TRI5 gene were individually spray- or point-inoculated onto Arabidopsis and wheat floral tissue. Disease development was quantitatively assessed both macroscopically and microscopically and deoxynivalenol (DON) mycotoxin concentrations determined by enzyme-linked immunosorbent assay (ELISA). Wild-type strain inoculations caused high levels of disease in both plant species and significant DON production. The map1 mutant caused minimal disease and DON accumulation in both hosts. The tri5 mutant, which is unable to produce DON, exhibited reduced pathogenicity on wheat ears, causing only discrete eye-shaped lesions on spikelets which failed to infect the rachis. By contrast, the tri5 mutant retained full pathogenicity on Arabidopsis floral tissue. This study reveals that DON mycotoxin production is not required for F. graminearum to colonize Arabidopsis floral tissue.     

Mapping QTLs with epistatic effects and QTL×environment interactions for plant height using a doubled haploid population in cultivated wheat

Quantitative trait loci (QTLs) for plant height in wheat (Triticum aestivum L.) were studied using a set of 168 doubled haploid (DH) lines, which were derived from the cross Huapei 3/Yumai 57. A genetic linkage map was constructed using 283 SSR and 22 EST-SSR markers. The DH population and the parents were evaluated for wheat plant height in 2005 and 2006 in Tai’an and 2006 in Suzhou. QTL analyses were performed using the software of QTLNetwork version 2.0 based on the mixed linear model. Four additive QTLs and five pairs of epistatic effects were detected, which were distributed on chromosomes 3A, 4B, 4D, 5A, 6A, 7B, and 7D. Among them, three additive QTLs and three pairs of epistatic QTLs showed QTL×environment interactions (QEs). Two major QTLs, Qph4B and Qph4D, which accounted for 14.51% and 20.22% of the phenotypic variation, were located similar to the reported locations of the dwarfing genes Rht1 and Rht2, respectively. The Qph3A-2 with additive effect was not reported in previous linkage mapping studies. The total QTL effects detected for the plant height explained 85.04% of the phenotypic variation, with additive effects 46.07%, epistatic effects 19.89%, and QEs 19.09%. The results showed that both additive effects and epistatic effects were important genetic bases of wheat plant height, which were subjected to environmental modifications, and caused dramatic changes in phenotypic effects. The information obtained in this study will be useful for manipulating the QTLs for wheat plant height by molecular marker-assisted selection (MAS).