The endophytic fungi from wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

In order to study the species composition of endophytes from wheat healthy plants in Buenos Aires Province (Argentina) and to determine their infection frequencies from leaves, stems, glumes and grains, wheat plants were collected from five cultivars at five growth stages from crop emergence to harvest. A total of 1,750 plant segments (leaves, stems, glumes and grains) were processed from the five wheat cultivars at five growth stages, and 722 isolates of endophytic fungi recovered were identified as 30 fungal genera. Alternaria alternata, Cladosporium herbarum, Epicoccum nigrum, Cryptococcus sp., Rhodotorula rubra, Penicillium sp. and Fusarium graminearum were the fungi that showed the highest colonization frequency (CF%) in all the tissues and organs analysed. The number of taxa isolated was greater in the leaves than those in the other organs analysed.     

Genotypic variation in drought stress response and subsequent recovery of wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Three wheat (Triticum aestivum L.) genotypes, Sadovo, Katya and Prelom, with different tolerance to drought were comparatively evaluated in terms of leaf respiratory responses to progressing dehydration and consecutive rewatering. Under drought stress, the respiration of all varieties gradually decreased, as the drought-tolerant Katya showed the most pronounced decline at earlier stages of dehydration. When water stress intensified, this genotype gave relatively stable respiration rates compared with the drought-sensitive varieties. Additionally, dehydrated Katya leaves displayed lower stomatal conductance and higher photosynthesis values, which resulted in greater water use efficiency during the dehydration period. Combination of drought stress and short-term changes in leaf temperature also induced genotype-specific response that differed from the response to drought only. Over the whole temperature range, the leaves of Katya exposed to dehydration for 14 days, showed higher respiration rates compared to the drought-sensitive varieties. The sensitive varieties maintained higher respiration rates under control conditions and mild dehydration, and very low rates under severe drought. In Katya, respiration and photosynthesis were fully restored from the stress within the first day of rewatering. The drought-sensitive genotypes displayed a considerably slower recovering capacity. The results are discussed in terms of possible physiological mechanisms underlying plant tolerance to drought.     

The parameters of grain filling and yield components in common wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) and durum wheat (<Emphasis Type="Italic">Triticum turgidum</Emphasis> L. var. <Emphasis Type="Italic">durum</Emphasis>)

Final grain dry weight, a component of yield in wheat, is dependent on the duration and the rate of grain filling. The purpose of the study was to compare the grain filling patterns between common wheat, (Triticum aestivum L.), and durum wheat, (Triticum turgidum L. var. durum), and investigate relationships among grain filling parameters, yield components and the yield itself. The most important variables in differentiating among grain filling curves were final grain dry weight (W) for common wheat genotypes and grain filling rate (R) for durum wheat genotypes; however, in all cases the sets of variables important in differentiating among grain filling curves were extended to either two or all three parameters. Furthermore, in one out of three environmental conditions and for both groups of genotypes, the most important parameter in the set was grain filling duration (T). It indicates significant impact of environmental conditions on dry matter accumulation and the mutual effect of grain filling duration and its rate on the final grain dry weight. The medium early anthesis date could be associated with further grain weight and yield improvements in wheat. Grain filling of earlier genotypes occurs in more temperate environments, which provides enough time for gradual grain fill and avoids the extremes of temperature and the stress of dry conditions.     

Antioxidative protection and proteolytic activity in tolerant and sensitive wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) varieties subjected to long-term field drought

Field drought studies were performed in order to assess oxidative stress, proteolytic activity and yield loss under natural stress conditions. Flag leaves of two drought-tolerant (Yantar and Zlatitsa) and two drought-sensitive (Miziya and Dobrudjanka) winter wheat varieties were analyzed. Stress intensity was assessed by relative electrolyte leakage and proline accumulation. Senescence progression was followed by loss of chlorophyll and protein. Lipid peroxidation, H₂O₂ content, activities of superoxide dismutase (SOD), catalase (CAT), and non-specific peroxidase (GPX) isoforms, as well as proteolytic activities were analyzed from heading throughout grain filling. Weakening of membrane integrity and oxidative damage to lipids were more pronounced in the sensitive varieties under field drought. The activities of Fe- and Cu/Zn SOD isoforms decreased in the controls, but remained high in drought-treated plants. The activities of MnSOD isoforms and CAT were enhanced towards grain filling, especially in the sensitive varieties under drought. GPX activities were rised under drought but progressively diminished. Accelerated senescence under field drought was linked to higher proteolytic activity with variety specific differences in the protease response, but without a clear correlation to drought resistance or sensitivity. Field drought led to higher oxidative stress more pronounced for drought sensitive varieties, especially during the grain filling period.     

Overexpression of <Emphasis Type="Italic">AtHDG11</Emphasis> enhanced drought tolerance in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Drought is one of the major abiotic stresses restricting the yield of wheat (Triticum aestivum L.). Breeding wheat varieties with drought tolerance is an effective and durable way to fight against drought. Here we reported introduction of AtHDG11 into wheat via Agrobacterium-mediated transformation and analyzed the morphological and physiological characteristics of T2 generation transgenic lines under drought stress. With drought treatment for 30 days, transgenic plants showed significantly improved drought tolerance. Compared with controls, the transgenic lines displayed lower stomatal density, lower water loss rate, more proline accumulation and increased activities of catalase and superoxide dismutase. Without irrigation after booting stage, the photosynthetic parameters, such as net photosynthesis rate, water use efficiency and efficiency of excitation energy, were increased in transgenic lines, while transpiration rate was decreased. Moreover, the kernel yield of transgenic lines was also improved under drought condition. Taken together, our data demonstrate that AtHDG11 has great potential in genetic improvement of drought tolerance of wheat.     

Drought-induced changes in photosynthetic membranes of two wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) cultivars

Two wheat (Triticum aestivum L.) cultivars contrasting in architectonics and differing in drought resistance, Azamatli-95 (short stature, vertically oriented small leaves, drought-tolerant) and Giymatli-2/17 (short stature, broad and drooping leaves, drought-sensitive), were studied. It was found that the content of CP I (115 kDa) and 63-kDa apoprotein P700 and also LHC II polypeptides increases slightly in the drought-resistant cv. Azamatli-95 under extreme water supply limitation, while their content decreases in drought-sensitive cv. Giymatli-2/17. The intensity of synthesis of α- and β-subunits of CF₁ (55 and 53.5 kDa) and 33–30.5 kDa proteins also decreases in the sensitive genotype. The intensity of short wavelength peaks at 687 and 695 nm sharply increases in the fluorescence spectra (77K) of chloroplasts from Giymatli-2/17 under water deficiency, and there is a stimulation of the ratio of fluorescence band intensity F687/F740. After exposure to drought, cv. Giymatli-2/17 shows a larger reduction in the actual PS II photochemical efficiency of chloroplasts than cv. Azamatli-95. Published in Russian in Biokhimiya, 2009, Vol. 74, No. 8, pp. 1109–1116.     

Gene expression changes in response to drought stress in <Emphasis Type="Italic">Citrullus colocynthis</Emphasis>

Citrullus colocynthis (L.) Schrad, closely related to watermelon, is a member of the Cucurbitaceae family. This plant is a drought-tolerant species with a deep root system, widely distributed in the Sahara-Arabian deserts in Africa and the Mediterranean region. cDNA amplified fragment length polymorphism (cDNA-AFLP) was used to study differential gene expression in roots of seedlings in response to a 20% polyethylene glycol-(PEG8000) induced drought stress treatment. Eighteen genes which show similarity to known function genes were confirmed by quantitative relative (RQ) real-time RT-PCR to be differentially regulated. These genes are involved in various abiotic and biotic stress and developmental responses. Dynamic changes with tissue-specific pattern were detected between 0 and 48 h of PEG treatment. In general, the highest induction levels in roots occurred earlier than in shoots, because the highest expression was detected in roots following 4 and 12 h, in shoots following 12 and 48 h of drought. These drought-responsive genes were also affected by the plant hormones abscisic acid (ABA), salicylic acid (SA), or jasmonic acid (JA), indicating an extensive cross-talk between drought and plant hormones. Collectively, these results will be useful to explore the functions of these multiple signal-inducible genes for unveiling the relationship and crosstalk between different signaling pathways.     

<Emphasis Type="Italic">In silico</Emphasis> physical mapping software for the <Emphasis Type="Italic">Triticum aestivum</Emphasis> genome

The large size of the Triticum aestivum genome makes it unlikely that a complete genome sequence for wheat will be available in the near future. Exploiting the conserved genome organization between wheat and rice and existing genomic resources, we have constructed in silico physical mapping software for wheat, assigning a gross physical location(s) into chromosome bins to 22,626 representative wheat gene sequences. To validate the predictions from the software we compared the predicted locations of ten ESTs to their positions experimentally determined by SNP marker analysis. Six of the sequences were correctly positioned on the map including four that demonstrated a high level of colinearity with their orthologous rice genomic region. This tool will facilitate the development of molecular markers for regions of interest and the creation of map-based cloning strategies in areas demonstrating high levels of sequence conservation and organization between wheat and rice.     

Genetic analysis of <Emphasis Type="Italic">Vrn-B1</Emphasis> for vernalization requirement by using linked dCAPS markers in bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

To identify a molecular marker closely linked to Vrn-B1, the Vrn-1 ortholog on chromosome 5B, sequence polymorphism at four orthologous RFLP loci closely linked to the Vrn-1 gene family was analyzed by using near-isogenic lines of ”Triple Dirk.” At Xwg644, a RFLP locus, three types of nucleotide sequence differing by the number of (TG) repeats, two or three times, and base changes were detected. A (TG)₃-type sequence proved to be specific to chromosome 5B by nulli-tetrasomic analysis, and substitution of single nucleotide (C/T) was detected between TD(B) carrying the former Vrn2 allele and TD(C) carrying the vrn2 allele. A mismatch primer was designed for dCAPS analysis of this single nucleotide polymorphism (SNP). Polymorphism was successfully detected between two NILs, through nested PCR by using a (TG)₃-specific primer (1st) and a dCAPS primer (2nd) followed by a NsiI digest. The analysis of a BF₂ population [(TD(B)//TD(C)] revealed the close linkage (1.7 cM) between WG644–5B and Vrn2. It was therefore concluded that the former Vrn2 locus is located on chromosome 5B and equivalent to Vrn-B1. Received: 3 May 2001 / Accepted: 19 July 2001     

Cloning and characterization of microRNAs from wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Background  

MicroRNAs (miRNAs) are a class of small, non-coding regulatory RNAs that regulate gene expression by guiding target mRNA cleavage or translational inhibition. So far, identification of miRNAs has been limited to a few model plant species, such as Arabidopsis, rice and Populus, whose genomes have been sequenced. Wheat is one of the most important cereal crops worldwide. To date, only a few conserved miRNAs have been predicted in wheat and the computational identification of wheat miRNAs requires the genome sequence, which is unknown.     

Structure and expression of the <Emphasis Type="Italic">TaGW7</Emphasis> in bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

OsGW7 (also known as OsGL7) is homologous to the Arabidopsis thaliana gene that encodes LONGIFOLIA protein, which regulates cell elongation, and is involved in regulating grain length in rice. However, our knowledge on its ortholog in wheat, TaGW7, is limited. In this study, we identified and mapped TaGW7 in wheat, characterized its nucleotide and protein structures, predicted the cis-elements of its promoter, and analysed its expression patterns. The GW7 orthologs in barley (HvGW7), rice (OsGW7), and Brachypodium distachyon (BdGW7) were also identified for comparative analyses. TaGW7 mapped onto the short arms of group 2 chromosomes (2AS, 2BS, and 2DS). Multiple alignments indicated GW7 possesses five exons and four introns in all but two of the species analysed. An exon–intron junction composed of introns 3–4 and exons 4–5 was highly conserved. GW7 has a conserved domain (DUF 4378) and two neighbouring low complexity regions. GW7 was mainly expressed in wheat spikes and stems, in barley seedling crowns, and in rice anthers and embryo-sacs during early development. Drought and heat significantly increased and decreased GW7 expression in wheat, respectively. In barley, GW7 was significantly down-regulated in paleae and awns but up-regulated in seeds under drought treatment and down-regulated under Fusarium and stem rust inoculation. In rice, OsGW7 expression differed significantly under drought treatments. Collectively, these results provide insights into GW7 structure and expression in wheat, barley and rice. The GW7 sequence structure and expression data are the foundation for manipulating GW7 and uncovering its roles in plants.     

Genetic architecture of seed longevity in bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

The deterioration in the quality of ex situ conserved seed over time reflects a combination of both physical and chemical changes. Intraspecific variation for longevity is, at least in part, under genetic control. Here, the grain of 183 bread wheat accessions maintained under low-temperature storage at the IPK-Gatersleben genebank over some decades have been tested for their viability, along with that of fresh grain subjected to two standard artificial ageing procedures. A phenotype–genotype association analysis, conducted to reveal the genetic basis of the observed variation between accessions, implicated many regions of the genome, underling the genetic complexity of the trait. Some, but not all, of these regions were associated with variation for both natural and experimental ageing, implying some non-congruency obtains between these two forms of testing for longevity. The genes underlying longevity appear to be independent of known genes determining dormancy and pre-harvest sprouting.