wheat
not annotated - annotated - LINNAEUS only
20955813
Comparative sequence analysis of wheat and barley powdery mildew fungi reveals gene colinearity, dates divergence and indicates host-pathogen co-evolution.
The two fungal pathogens Blumeria graminis f. sp. triticiBlumeria graminis f. sp. tritici (B.g. tritici) and hordei (B.g. hordei) cause powdery mildew specifically in wheat or barley. They have the same life cycle, but their growth is restricted to the respective host. Here, we compared the sequences of two loci in both cereal mildews to determine their divergence time and their relationship with the evolution of their hosts. We sequenced a total of 273.3kb derived from B.g. tritici BAC sequences and compared them with the orthologous regions in the B.g. hordei genome. Protein-coding genes were colinear and well conserved. In contrast, the intergenic regions showed very low conservation mostly due to different integration patterns of transposable elements. To estimate the divergence time of B.g. tritici and B.g. hordei, we used conserved intergenic sequences including orthologous transposable elements. This revealed that B.g. tritici and B.g. hordei have diverged about 10 million years ago (MYA), two million years after wheat and barley (12 MYA). These data suggest that B.g. tritici and B.g. hordei have co-evolved with their hosts during most of their evolutionary history after host divergence, possibly after a short phase of host expansion when the same pathogen could still grow on the two diverged hosts.
20971913
Structural and functional analysis of the type III secretion system from Pseudomonas fluorescens Q8r1-96.
Pseudomonas fluorescens Q8r1-96 represents a group of rhizosphere strains responsible for the suppressiveness of agricultural soils to take-all disease of wheat. It produces the antibiotic 2,4-diacetylphloroglucinol and aggressively colonizes the roots of cereal crops. In this study, we analyzed the genome of Q8r1-96 and identified a type III protein secretion system (T3SS) gene cluster that has overall organization similar to that of the T3SS gene cluster of the plant pathogen Pseudomonas syringae. We also screened a collection of 30 closely related P. fluorescens strains and detected the T3SS genes in all but one of them. The Q8r1-96 genome contained ropAA and ropM type III effector genes, which are orthologs of the P. syringae effector genes hopAA1-1 and hopM1, as well as a novel type III effector gene designated ropB. These type III effector genes encoded proteins that were secreted in culture and injected into plant cells by both P. syringae and Q8r1-96 T3SSs. The Q8r1-96 T3SS was expressed in the rhizosphere, but mutants lacking a functional T3SS were not altered in their rhizosphere competence. The Q8r1-96 type III effectors RopAA, RopB, and RopM were capable of suppressing the hypersensitive response and production of reactive oxygen species, two plant immune responses.
21029104
Improved nitrogen nutrition enhances root uptake, root-to-shoot translocation and remobilization of zinc ((65) Zn) in wheat.
This study focussed on the effect of increasing nitrogen (N) supply on root uptake and root-to-shoot translocation of zinc (Zn) as well as retranslocation of foliar-applied Zn in durum wheat (Triticum durum). Nutrient solution experiments were conducted to examine the root uptake and root-to-shoot translocation of (65) Zn in seedlings precultured with different N supplies. In additional experiments, the effect of varied N nutrition on retranslocation of foliar-applied (65) Zn was tested at both the vegetative and generative stages. When N supply was increased, the (65) Zn uptake by roots was enhanced by up to threefold and the (65) Zn translocation from roots to shoots increased by up to eightfold, while plant growth was affected to a much smaller degree. Retranslocation of (65) Zn from old into young leaves and from flag leaves to grains also showed marked positive responses to increasing N supply. The results demonstrate that the N-nutritional status of wheat affects major steps in the route of Zn from the growth medium to the grain, including its uptake, xylem transport and remobilization via phloem. Thus, N is a critical player in the uptake and accumulation of Zn in plants, which deserves special attention in biofortification of food crops with Zn.
21039562
Haplotype analysis of the genes encoding glutamine synthetase plastic isoforms and their association with nitrogen-use- and yield-related traits in bread wheat.
Glutamine synthetase (GS) plays a key role in the growth, nitrogen (N) use and yield potential of cereal crops. Investigating the haplotype variation of GS genes and its association with agronomic traits may provide useful information for improving wheat N-use efficiency and yield. We isolated the promoter and coding region sequences of the plastic glutamine synthetase isoform (GS2) genes located on chromosomes 2A, 2B and 2D in bread wheat. By analyzing nucleotide sequence variations of the coding region, two, six and two haplotypes were distinguished for TaGS2-A1 (a and b), TaGS2-B1 (a-f) and TaGS2-D1 (a and b), respectively. By analyzing the frequency data of different haplotypes and their association with N use and agronomic traits, four major and favorable TaGS2 haplotypes (A1b, B1a, B1b, D1a) were revealed. These favorable haplotypes may confer better seedling growth, better agronomic performance, and improved N uptake during vegetative growth or grain N concentration. Our data suggest that certain TaGS2 haplotypes may be valuable in breeding wheat varieties with improved agronomic performance and N-use efficiency.
21216300
The genetic basis for 3-ADON and 15-ADON trichothecene chemotypes in Fusarium.
Certain Fusarium species cause head blight of wheat and other small grains worldwide and produce trichothecene mycotoxins. These mycotoxins can induce toxicoses in animals and humans and can contribute to the ability of some fusaria to cause plant disease. Production of the trichothecene 3-acetyldeoxynivalenol (3-ADON) versus 15-acetyldeoxynivalenol (15-ADON) is an important phenotypic difference within and among some Fusarium species. However, until now, the genetic basis for this difference in chemotype has not been identified. Here, we identified consistent DNA sequence differences in the coding region of the trichothecene biosynthetic gene TRI8 in 3-ADON and 15-ADON strains. Functional analyses of the TRI8 enzyme (Tri8) in F. graminearum, the predominant cause of wheat head blight in North America and Europe, revealed that Tri8 from 3-ADON strains catalyzes deacetylation of the trichothecene biosynthetic intermediate 3,15-diacetyldeoxynivalenol at carbon 15 to yield 3-ADON, whereas Tri8 from 15-ADON strains catalyzes deacetylation of 3,15-diacetyldeoxynivalenol at carbon 3 to yield 15-ADON. Fusarium strains that produce the trichothecene nivalenol have a Tri8 that functions like that in 15-ADON strains. TRI3, which encodes a trichothecene carbon 15 acetyltransferase, was found to be functional in all three chemotypes. Together, our data indicate that differential activity of Tri8 determines the 3-ADON and 15-ADON chemotypes in Fusarium.
21062315
Cold stress contributes to aberrant cytokinesis during male meiosis I in a wheat thermosensitive genic male sterile line.
The male sterility of a wheat thermosensitive genic male sterile (TGMS) line is strictly controlled by temperature. When the TGMS line BS366 was exposed to 10 ^0C from the pollen mother cell stage to the meiosis stage, a few pollen grains were formed and devoid of starch. We report here a large-scale transcriptomic study using the Affymetrix wheat GeneChip to follow gene expression in BS366 line anthers in response to cold stress. Notably, many cytoskeletal signaling components were gradually induced in response to cold stress in BS366 line anthers. However, the cytoskeleton-associated genes that play key roles in the dynamic organization of the cytoskeleton were dramatically repressed. Histological studies revealed that the separation of dyads occurred abnormally during male meiosis I, indicating defective male meiotic cytokinesis. Fluorescence labelling and subcellular histological observations revealed that the phragmoplast was defectively formed and the cell plate was abnormally assembled during meiosis I under cold stress. Based on the transcriptomic analysis and observations of characterized histological changes, our results suggest that cold stress repressed transcription of cytoskeleton dynamic factors and subsequently caused the defective cytokinesis during meiosis I. The results may explain the male sterility caused by low temperature in wheat TGMS lines.
21397712
Npc1 is involved in sterol trafficking in the filamentous fungus Fusarium graminearum.
The ortholog of the human gene NPC1 was identified in the plant pathogenic, filamentous fungus Fusarium graminearum by shared amino acid sequence, protein domain structure and cellular localization of the mature fungal protein. The FusariumNpc1 gene shares 34% amino acid sequence identity and 51% similarity to the human gene, has similar domain structure and is constitutively expressed, although up-regulated in ungerminated macroconidia and ascospores. GFP-tagged Npc1p localizes to the fungal vacuolar membrane. Cultures derived from a Deltanpc1 mutant strain contain significantly more ergosterol than cultures of the wildtype. Staining with the fluorescent, sterol binding dye filipin, shows that ergosterol accumulates in vacuoles of the Deltanpc1 mutant but not the wildtype strain. The Deltanpc1 mutant has a temperature dependent reduction in growth and greater sensitivity to the ergosterol synthesis inhibiting fungicide tebuconazole compared with the wildtype strain or the mutant complemented with wildtype Npc1. The mutant also is significantly reduced in pathogenicity to wheat. Our results are consistent with the interpretation that Npc1p is important for normal transport of ergosterol from the vacuole and is essential for proper membrane function under particular environmental conditions.
21601644
Analysis of the Fusarium graminearum species complex from wheat, barley and maize in South Africa provides evidence of species-specific differences in host preference.
Species identity and trichothecene toxin potential of 560 members of the Fusarium graminearum species complex (FGSC) collected from diseased wheat, barley and maize in South Africa was determined using a microsphere-based multilocus genotyping assay. Although three trichothecene types (3-ADON, 15-ADON and NIV) were represented among these isolates, strains with the 15-ADON type predominated on all three hosts. A significant difference, however, was identified in the composition of FGSC pathogens associated with Gibberella ear rot (GER) of maize as compared to Fusarium head blight (FHB) of wheat or barley (P<0.001). F. graminearum accounted for more than 85% of the FGSC isolates associated with FHB of wheat and barley (N=425), and was also the dominant species among isolates from maize roots (N=35). However, with the exception of a single isolate identified as an interspecific hybrid between Fusariumboothii and F. graminearum, GER of maize (N=100) was exclusively associated with F. boothii. The predominance of F. graminearum among FHB isolates, and the near exclusivity of F. boothii among GER isolates, was observed across all cultivars, collection dates, and provinces sampled. Because these results suggest a difference in host preference among species of the FGSC, we hypothesize that F. graminearum may be less well adapted to infect maize ears than other members of the FGSC.
20946419
Stable isotope labelling and zinc distribution in grains studied by laser ablation ICP-MS in an ear culture system reveals zinc transport barriers during grain filling in wheat.
Zinc (Zn) deficiency has been recognized as a potential risk for human health in many developing regions where staple food with low micronutrient density represents a major proportion of the diet. The success of strategies to increase Zn content in the edible part of crops requires better understanding of Zn transport to, and distribution within, the grains. The transfer of Zn from the growth medium to wheat (Triticum aestivum) grains in an ear culture system was investigated by using the stable Zn isotope (70) Zn, and the spatial distribution of Zn within the grains was studied by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Zinc was readily transported in the stem up to the rachis. More Zn accumulated in the stem when higher amounts of Zn were supplied to the medium. Once Zn was transported into the grain, Zn accumulated particularly in the crease vascular tissue. The gradient of (70) Zn concentration between crease vascular tissue, aleurone layer and endosperm demonstrates that Zn is distributed within grain through the crease phloem. These results suggest that two barriers of Zn transport into wheat grains may exist: between the stem tissue rachis and the grain, and the maternal and filial tissues in the grain.
21062317
Dual Delta^1^3C/delta^1^8O response to water and nitrogen availability and its relationship with yield in field-grown durum wheat.
The combined use of stable carbon and oxygen isotopes in plant matter is a tool of growing interest in cereal crop management and breeding, owing to its relevance for assessing the photosynthetic and transpirative performance under different growing conditions including water and N regimes. However, this method has not been applied to wheat grown under real field conditions. Here, plant growth, grain yield (GY) and the associated agronomic components, carbon isotope discrimination (Delta^1^3C) plus oxygen isotope composition (delta^1^8O) as well as leaf and canopy gas exchange were measured in field-grown wheat subjected to different water and N availabilities. Water limitation was the main factor affecting yield, leaf and canopy gas exchange and Delta^1^3C and delta^1^8O, whereas N had a smaller effect on such traits. The combination of Delta^1^3C and delta^1^8O gave a clear advantage compared with gas exchange measurements, as it provides information on the instantaneous and the long-term plant photosynthetic and transpirative performance and are less labour intensive than gas exchange measurements. In addition, the combination of plant Delta^1^3C and delta^1^8O predicted differences in GY and related agronomical parameters, providing agronomists and breeders with integrative traits for selecting crop management practices and/or genotypes with better performance under water-limiting and N-limiting conditions.
21251018
Using tunable diode laser spectroscopy to measure carbon isotope discrimination and mesophyll conductance to CO2 diffusion dynamically at different CO2 concentrations.
In C3 leaves, the mesophyll conductance to CO2 diffusion, g(m) , determines the drawdown in CO2 concentration from intercellular airspace to the chloroplast stroma. Both g(m) and stomatal conductance limit photosynthetic rate and vary in response to the environment. We investigated the response of g(m) to changes in CO2 in two Arabidopsis genotypes (including a mutant with open stomata, ost1), tobacco and wheat. We combined measurements of gas exchange with carbon isotope discrimination using tunable diode laser absorption spectroscopy with a CO2 calibration system specially designed for a range of CO2 and O2 concentrations. CO2 was initially increased from 200 to 1000 ppm and then decreased stepwise to 200 ppm and increased stepwise back to 1000 ppm, or the sequence was reversed. In 2% O2 a step increase from 200 to 1000 ppm significantly decreased g(m) by 26-40% in all three species, whereas following a step decrease from 1000 to 200 ppm, the 26-38% increase in g(m) was not statistically significant. The response of g(m) to CO2 was less in 21% O2. Comparing wild type against the ost1 revealed that mesophyll and stomatal conductance varied independently in response to CO2. We discuss the effects of isotope fractionation factors on estimating g(m) .
22004876
Novel Fusarium head blight pathogens from Nepal and Louisiana revealed by multilocus genealogical concordance.
This study was conducted to assess evolutionary relationships, species diversity and trichothecene toxin potential of five Fusarium graminearum complex (FGSC) isolates identified as genetically novel during prior Fusarium head blight (FHB) surveys in Nepal and Louisiana. Results of a multilocus genotyping (MLGT) assay for B-trichothecene species determination indicated these isolates might represent novel species within the FGSC. GCPSR-based phylogenetic analyses of a 12-gene dataset, comprising portions of seven loci totaling 13.1kb of aligned DNA sequence data, provided strong support for the genealogical exclusivity of the Nepalese and Louisianan isolates. Accordingly, both species are formally recognized herein as novel FGSC species. Fusarium nepalense was resolved as the sister lineage of Fusarium ussurianum+Fusarium asiaticum within an Asian subclade of the FGSC. Fusarium louisianense was strongly supported as a reciprocally monophyletic sister of Fusarium gerlachii+F. graminearum, suggesting that this subclade might be endemic to North America. Multilocus Bayesian species tree analyses augment these results and provide evidence for a distinct lineage within F. graminearum predominately from the Gulf Coast of Louisiana. As predicted by the MLGT assay, mycotoxin analyses demonstrated that F. nepalense and F. louisianense could produce 15ADON and nivalenol, respectively, in planta. In addition, both species were only able to induce mild FHB symptoms on wheat in pathogenicity experiments.