RFLP Variations of Common Wheat Doubled Haploid Progenies from Wheat×Maize Crosses

Wheat ( Triticum aestivum L. ) and maize ( Zea mays L. ) crosses (the chromosome elimination system) can be used to produce frequently a large number of doubled haploid (DH) wheat lines by embryo rescue and doubling treatment. The resulting DH lines are genetically homogeneous. Significant RFLP variations were detected in common wheat DH progenies from wheat and maize crosses by using wheat rDNA clone pta71 and two maize DNA clones (MR13 and MRSO) homologous to wheat genome as probes. The results revealed that the copy number and restriction fragment length of rDNA in some wheat DH progenies was changed, and also that deletion was detected in several DH plants when probed with MR13 and MR5O. In particular, the RFLP pattern of DH line No. 18 was greatly changed using MR13 as a probe. In this line, three new bands, 40.0 kb, 2.5 kb and 2.0 kb emerged while a 4.3 kb intense band from the parental common wheat genome disappeared. This change may be related to a quite large DNA rearrangement within the wheat genomic DNA or an insertion by alien maize DNA fragment.     

Electrophoretic Survey of Proteins and Esterase Isozyme in Wheat×Maize Progenies

The analysis of soluble proteins and esterase isozyme in F2 progeny grains from wheat (Triticum aestivum L. ) × maize (Zea mays L. ) crosses indicated that the electrophoretic pattern of proteins and esterase isozymes was extremely different from that of their parents. Protein variation was mainly concentrated in the high-molecular-weight-Glu (HMW-Glu) zone. There were 5 kinds of protein eleetrophoretic patterns in the analyzed grains. VIZ: maternal, additional, complementary, hybrid and omission type which accounted for 22.6%, 14.3%, 15.5%, 30. 9% and 16.7% of the total tested grains respectively. In the analysis of esterase pattern, some variations in progenies were also found. The variations of electrophoretic pattern of proteins and esterase isozyme indicated that a genetic material change in wheat chromosomes could be induced in the distant hybridization.     

Soil Type and Maize Cultivar Affect the Genetic Diversity of Maize Root–Associated Burkholderia cepacia Populations

Abstract Burkholderia cepacia populations associated with the Zea mays root system were investigated to assess the influence of soil type, maize cultivar, and root localization on the degree of their genetic diversity. A total of 180 B. cepacia isolates were identified by restriction analysis of the amplified 16S rDNA (ARDRA technique). The genetic diversity among B. cepacia isolates was analyzed by the random amplified polymorphic DNA (RAPD) technique, using the 10-mer primer AP5. The analysis of molecular variance (AMOVA) method was applied to estimate the variance components for the RAPD patterns. The results indicated that, among the factors studied, the soil was clearly the dominant one in affecting the genetic diversity of maize root–associated B. cepacia populations. In fact, the percentage of variation among populations was significantly higher between B. cepacia populations recovered from maize planted in different soils than between B. cepacia populations isolated from different maize cultivars and from distinct root compartments such as rhizoplane and rhizosphere. The analysis of the genetic relationships among B. cepacia isolates resulted in dendrograms showing bacterial populations with frequent recombinations and a nonclonal genetic structure. The dendrograms were also in agreement with the AMOVA results. We were able to group strains obtained from distinct soils on the basis of their origin, confirming that soil type had the major effect on the degree of genetic diversity of the maize root–associated B. cepacia populations analyzed. On the other hand, strains isolated from distinct root compartments exhibited a random distribution which confirmed that the rhizosphere and rhizoplane populations analyzed did not significantly differ in their genetic structure. Received: 22 January 1999; Accepted: 7 April 1999     

Spring Wheat Leaf Appearance and Temperature: Extending the Paradigm?

Extensive research shows temperature to be the primary environmental factor controlling the phyllochron, or rate of leaf appearance, of wheat (Triticum aestivum L.). Experimental results suggest that soil temperature at crown depth, rather than air temperature above the canopy, would better predict wheat leaf appearance rates. To test this hypothesis, leaf appearance in spring wheat ('Nordic') was measured in a 2-year field experiment (Nunn clay loam soil; fine, smectitic, mesic Aridic, Argiustoll) with three planting dates and two soil temperature treatments. One temperature treatment (denoted +3C) consisted of heating the soil at crown depth to 3 degrees C above the ambient soil temperature (denoted +0C). Main stem cumulative leaf number was measured at least weekly until flag leaf emergence. Leaf appearance was essentially linear with both air and soil growing degree-days (GDD), although there was a stronger linear relationship with soil GDD in the +0C plants than in +3C plants. A weak positive relationship between planting date and the phyllochron was observed. Unexpectedly, we found that heating the soil did not increase the rate of leaf appearance, as the paradigm would predict. To explain these results, we propose extending the paradigm in two ways. First, three processes are involved in leaf appearance: (1) cell division at the shoot apex forms the primordium; (2) cell division in the intercalary meristem forms the cells that then (3) expand to produce the leaf. Cell division is predominantly controlled by temperature, but cell expansion is considerably more affected by factors other than temperature, explaining the influence of other factors on the phyllochron. Secondly, the vertical distribution of the two meristems and region of cell expansion occur over a significant distance, where temperature varies considerably, and temperature at a specific point (e.g. crown depth) does not account for the entire temperature regime under which leaves are developing.     

Factors Affecting the Radiosensitivity of Hexaploid Wheat to γ-Irradiation: Radiosensitivity of Hexaploid Wheat (Triticum aestivum L.)

Understanding the radiosensitivity of plants, an important factor in crop mutation breeding programs, requires a thorough investigation of the factors that contribute to this trait. In this study, we used the highly radiosensitive wheat (Triticum aestivum L.) variety HY1 and J411, a γ-irradiation-insensitive control, which were screened from a natural population, to examine the factors affecting radiosensitivity, including free radical content and total antioxidant capacity, as well as the expression of TaKu70 and TaKu80 (DNA repair-related genes) as measured by real-time PCR. We also investigated the alternative splicing of this gene in the wild-type wheat ecotype by sequence analysis. Free radical contents and total antioxidant capacity significantly increased upon exposure of HY1 wheat to γ-irradiation in a dose-dependent manner. By contrast, in J411, the free radical contents exhibited a similar trend, but the total antioxidant capacity exhibited a downward trend upon increasing γ-irradiation. Additionally, we detected dose-dependent increases in TaKu70 and TaKu80 expression levels in γ-irradiated HY1, while in J411, TaKu70 expression levels increased, followed by a decline. We also detected alternative splicing of TaKu70 mRNA, namely, intron retention, in HY1 but not in J411. Our findings indicate that γ-irradiation induces oxidative stress and DNA damage in hexaploid wheat, resulting in growth retardation of seedlings, and they suggest that TaKu70 may play a causal role in radiosensitivity in HY1. Further studies are required to exploit these factors to improve radiosensitivity in other wheat varieties.     

Salinity Stiffens the Epidermal Cell Walls of Salt-Stressed Maize Leaves: Is the Epidermis Growth-Restricting?

As a result of salt (NaCl)-stress, sensitive varieties of maize (Zea mays L.) respond with a strong inhibition of organ growth. The reduction of leaf elongation investigated here has several causes, including a modification of the mechanical properties of the cell wall. Among the various tissues that form the leaf, the epidermis plays a special role in controlling organ growth, because it is thought to form a rigid outer leaf coat that can restrict elongation by interacting with the inner cell layers. This study was designed to determine whether growth-related changes in the leaf epidermis and its cell wall correspond to the overall reduction in cell expansion of maize leaves during an osmotic stress-phase induced by salt treatment. Two different maize varieties contrasting in their degree of salt resistance (i.e., the hybrids Lector vs. SR03) were compared in order to identify physiological features contributing to resistance towards salinity. Wall loosening-related parameters, such as the capacity of the epidermal cell wall to expand, β-expansin abundance and apoplastic pH values, were analysed. Our data demonstrate that, in the salt-tolerant maize hybrid which maintained leaf growth under salinity, the epidermal cell wall was more extensible under salt stress. This was associated with a shift of the epidermal apoplastic pH into a range more favourable for acid growth. The more sensitive hybrid that displayed a pronounced leaf growth-reduction was shown to have stiffer epidermal cell walls under stress. This may be attributable to the reduced abundance of cell wall-loosening β-expansin proteins following a high salinity-treatment in the nutrient solution (100 mM NaCl, 8 days). This study clearly documents that salt stress impairs epidermal wall-loosening in growth-reduced maize leaves.     

Naked Oat×Maize Hybridization

There is a certain frequency of fertilization and embryo productivity in naked oat (Avena nuda L. ) × maize (Zea mays L. ) crosses. The maize pollen readily germinated on the naked oat stigma and more than one pollen tubes grew into the style in about 68% of florets. In a sample of 163 florets fixed after pollination, 5 (3.07%) had only an embryo, 3 (1.84%) had only an endosperm and 10 (6.13%) had both. Overall, 9 haploid and 3 diploid naked oat plants were obtained from 12 seeds which formed following application of maize pollen to about 2200 emasculated naked oat florets. Preliminary studies indicated that elimination of the maize chromosomes occurred early in the embryo and endosperm development. This method gives a new approach for obtaining haplo!d naked oat.     

Morphological Variability of Wheat Powdery Mildew in the Context of Its Parasitic Adaptation to Wheat–Aegilops Lines with Different Resistance

The interaction between the pathogen and wheat–Aegilops lines with different resistance as well as their parental forms in the course of powdery mildew infection was studied using scanning electron microscopy. The course of infection in the line 51/99i and its parental form, the Rodina variety, proved to be similar. The plants of both genotypes featured pronounced adhesion of the primary infection structures to the surface of plant epidermal cells and the formation of large, well-developed colonies of the fungus, which was evidence for parasite–host compatibility. The development of powdery mildew on the line 135/99i was similar to that on the parental form Aegilops speltoides K-389. The pathogen–host interaction was characterized by a longer incubation period. Sparse fungal colonies were formed from mycelial hyphae with multiple hyphal lobes, and their adhesion to the surface of the epidermal cells was disturbed in most cases. Such a pattern of pathogen development indicated that the host plants had some resistance factors operating mainly at the level of pathogen penetration. The types of resistance in lines 95/99i and 56/99i were not characteristic of the parental form Ae. speltoides K-389, but they were described for Ae. speltoides samples from other natural ranges (Ryabchenko et al., 2002). This fact suggests that the immune potential of Ae. speltoides as a species is polygenic, and its elements can be transmitted to hybrids irrespective of concrete plants used as the donors of resistance.     

More Productive Than Maize in the Midwest: How Does Miscanthus Do It?

In the first side-by-side large-scale trials of these two C₄ crops in the U.S. Corn Belt, Miscanthus (Miscanthus × giganteus) was 59% more productive than grain maize (Zea mays). Total productivity is the product of the total solar radiation incident per unit land area and the efficiencies of light interception (ε_i) and its conversion into aboveground biomass (ε_ca). Averaged over two growing seasons, ε_ca did not differ, but ε_i was 61% higher for Miscanthus, which developed a leaf canopy earlier and maintained it later. The diurnal course of photosynthesis was measured on sunlit and shaded leaves of each species on 26 dates. The daily integral of leaf-level photosynthetic CO₂ uptake differed slightly when integrated across two growing seasons but was up to 60% higher in maize in mid-summer. The average leaf area of Miscanthus was double that of maize, with the result that calculated canopy photosynthesis was 44% higher in Miscanthus, corresponding closely to the biomass differences. To determine the basis of differences in mid-season leaf photosynthesis, light and CO₂ responses were analyzed to determine in vivo biochemical limitations. Maize had a higher maximum velocity of phosphoenolpyruvate carboxylation, velocity of phosphoenolpyruvate regeneration, light saturated rate of photosynthesis, and higher maximum quantum efficiency of CO₂ assimilation. These biochemical differences, however, were more than offset by the larger leaf area and its longer duration in Miscanthus. The results indicate that the full potential of C₄ photosynthetic productivity is not achieved by modern temperate maize cultivars.     

Expression of a Synthetic Porcine α-Lactalbumin Gene in the Kernels of Transgenic Maize

The main nutritional limitation of maize used for feed is the content of protein that is digestible, bioavailable and contains an amino acid balance that matches the requirements of animals. In contrast, milk protein has good digestibility, bioavailability and amino acid balance. As an initial effort to create maize optimized as a source of swine nutrition, a codon-adjusted version of a gene encoding the milk protein porcine -lactalbumin was synthesized. Maize expression vectors containing this gene under the control of the Ubi-1 promoter and nos 3 terminator were constructed. These vectors were used to transform maize callus lines that were regenerated into fertile plants. The -lactalbumin transgenes were transmitted through meiosis to the sexual progeny of the regenerated plants. Porcine -lactalbumin was detected in callus and kernels from transgenic maize lines that were transformed by two constructs containing the 27-kDa maize gamma-zein signal sequence at the 5 end of the synthetic porcine -lactalbumin coding sequence. One of these constructs contained an ER retention signal and the other did not. Expression was not observed in kernels or callus from transgenic maize lines that were transformed by a construct that does not contain an exogenous protein-targeting signal. This suggests that the signal peptide might play an important role in porcine -lactalbumin accumulation in transgenic maize kernels.     

Does ABA in the Xylem Control the Rate of Leaf Growth in Soil-Dried Maize and Sunflower Plants?

Maize (Zea mays L.) and sunflower (Helianthus annuus L.) plantswere grown in large volumes of soil and leaf growth rate wasmonitored on a daily basis. Half the plants were given a soildrying treatment and when they showed a significant restrictionof growth rate (compared to both their daily growth rate beforedrying and the average growth rate of well-watered plants onthe same day), leaf water relations were measured and xylemsap was extracted using several techniques. There was a significant negative log-linear relationship betweenthe rate of leaf growth and the concentration of ABA in thexylem for both species. There was no clear relationship betweenleaf growth rate and leaf water potential or turgor for eitherspecies. Assessment of different methods for sampling xylemsap suggests that exudates collected from stem stumps or samplescollected by pressurizing the whole root system are suitablefor estimating ABA concentration in xylem, at least with largeplants of maize or sunflower, provided the first few hundredcubic millimetres of collected sap are used for the assay. Centrifugationof sections of stems resulted in dilution of ABA in the xylemsap with sap squeezed from parenchyma tissue. This is because,at least in plants subjected to mild soil drying, the concentrationof the ABA in the xylem is far higher than that in the cellsap of stem tissue. Results support the proposal that ABA plays a major role asa chemical signal involved in the root-to-shoot communicationof the effects of soil drying. The non-hydraulic restrictionof leaf growth by a chemical signal can be explained by theextra root-sourced ABA in the xylem and may be an importantcomponent of the modification of growth and development whichresults from prolonged soil drought. Key words: Soil drying, ABA, leaf growth, Zea mays L., Helianthus annuus L.     

Functioning of the γ-Aminobutyrate Pathway in Wheat Seedlings Affected by Osmotic Stress

γ-Aminobutyrate (GABA) was the only amino acid out of three amino acid intermediates of GABA shunt that increased significantly after 28 h from the beginning of osmotic stress induced by 20 % polyethylene glycol 6000 in wheat seedlings. At the same time specific activities of glutamate decarboxylase (GAD) and GABA aminotransferase (GABA-T) two enzymes of GABA pathway did not change as compared with the control plants. The response of two GABA-T activities (with pyruvate or 2-oxoglutarate as amino acid acceptor) to aminooxyacetate, 3-chloro-L-alanine and p-hydroxymercuribenzoate prompted us to suggest that at least two isoforms of GABA-T showing different substrate specificity do exist in wheat leaves. This revised version was published online in July 2006 with corrections to the Cover Date.     

Defects in Mitochondrial and Peroxisomal β-Oxidation Influence Virulence in the Maize Pathogen Ustilago maydis

An understanding of metabolic adaptation during the colonization of plants by phytopathogenic fungi is critical for developing strategies to protect crops. Lipids are abundant in plant tissues, and fungal phytopathogens in the phylum basidiomycota possess both peroxisomal and mitochondrial β-oxidation pathways to utilize this potential carbon source. Previously, we demonstrated a role for the peroxisomal β-oxidation enzyme Mfe2 in the filamentous growth, virulence, and sporulation of the maize pathogen Ustilago maydis. However, mfe2 mutants still caused disease symptoms, thus prompting a more detailed investigation of β-oxidation. We now demonstrate that a defect in the had1 gene encoding hydroxyacyl coenzyme A dehydrogenase for mitochondrial β-oxidation also influences virulence, although its paralog, had2, makes only a minor contribution. Additionally, we identified a gene encoding a polypeptide with similarity to the C terminus of Mfe2 and designated it Mfe2b; this gene makes a contribution to virulence only in the background of an mfe2Δ mutant. We also show that short-chain fatty acids induce cell death in U. maydis and that a block in β-oxidation leads to toxicity, likely because of the accumulation of toxic intermediates. Overall, this study reveals that β-oxidation has a complex influence on the formation of disease symptoms by U. maydis that includes potential metabolic contributions to proliferation in planta and an effect on virulence-related morphogenesis.     

Influence of Macroelements’ Uneven Distribution on the Content of Hormones and Extension of the Roots in Wheat Plants

Russian Journal of Plant Physiology - Increase in the level of mineral nutrition reduces the relative growth rate of the roots, which adversely affects the drought resistance of plants. This was...     

ZmcrtRB3 Encodes a Carotenoid Hydroxylase that Affects the Accumulation of α-carotene in Maize Kernel

α-carotene is one of the important components of pro-vitamin A,which is able to be converted into vitamin A in the human body.One maize(Zea mays L.) ortholog of carotenoid hydroxylases in Arabidopsis thaliana,ZmcrtRB3,was cloned and its role in carotenoid hydrolyzations was addressed.ZmcrtRB3 was mapped in a quantitative trait locus(QTL) cluster for carotenoid-related traits on chromosome 2(bin 2.03) in a recombinant inbred line(RIL) population derived from By804 and B73.Candidate-gene association analysis identified 18 polymorphic sites in ZmcrtRB3 significantly associated with one or more carotenoid-related traits in 126 diverse yellow maize inbred lines.These results indicate that the enzyme ZmcrtRB3 plays a role in hydrolyzing both α-and β-carotenes,while polymorphisms in ZmcrtRB3 contributed more variation in α-carotene than that in β-carotene.Two single nucleotide polymorphisms(SNPs),SNP1343 in 5 untranslated region and SNP2172 in the second intron,consistently had effects on α-carotene content and composition with explained phenotypic variations ranging from 8.7% to 34.8%.There was 1.7-to 3.7-fold change between the inferior and superior haplotype for α-carotene content and composition.Thus,SNP1343 and SNP2172 are potential polymorphic sites to develop functional markers for applying marker-assisted selection in the improvement of pro-vitamin A carotenoids in maize kernels.     

Wheat protein inhibitors of α-amylase

The location in the seed, molecular properties and biological role of protein α-amylase inhibitors from wheat are discussed. Inhibition specificity of albumin inhibitors and structural features essential for interaction with inhibited amylases are also examined. The possible significance of these naturally occurring inhibitors in relation to their presence in foods in active form is described. Finally, genetic aspects of the albumin inhibitor production and the possibility of improving nutritional value and insect re     

Substitutions of the Conserved Thr42 Increased the Roles of the ε-Subunit of Maize CF1 as CF1 Inhibitor and Proton Gate

The conserved residue Thr42 of -subunit of the chloroplast ATP synthase of maize (Zea mays L.) was substituted with Cys, Arg, and Ile, respectively, through site-directed mutagenesis. The over-expressed and refolded -proteins were purified by chromatography on DEAE-cellulose and FPLC on mono-Q column, which were as biologically active (inhibiting Ca²⁺-ATPase activity and blocking proton gate) as the native subunit isolated from chloroplasts. The T42C and T42R showed higher inhibitory activities on the soluble CF₁(–) Ca²⁺-ATPase than the WT. The T42I inhibited the Ca²⁺-ATPase activity of soluble CF₁ and restored photophosphorylation activity of membrane-bound CF₁ deficient in the most efficiently. Far-ultraviolet CD spectra showed that the portions of -helix and -sheet structures of the three mutants were somewhat different from WT. Thus the conserved residue Thr42 may be important for maintaining the structure and function of the -subunit and the basic functions of the -subunit as far as an inhibitor of Ca²⁺-ATPase and the proton gate are related.     

Maize AKINβγ dimerizes through the KIS/CBM domain and assembles into SnRK1 complexes

The SNF1/AMPK/SnRK1 complex is an intracellular energy sensor composed of three types of subunits: the SnRK1 kinase and two regulatory, non-catalytic subunits (designated β and γ). We have previously described an atypical plant γ-subunit, AKINβγ, which contains an N-terminal tail similar to the so-called KIS domain normally present in β-subunits. However, it is not known whether AKINβγ normally associates with endogenous SnRK1 complexes in vivo, nor how its unique domain structure might contribute to SnRK1 function. Here, we present evidence that maize AKINβγ is an integral component of active SnRK1 complexes in plant cells. Using complementary methodological approaches, we also show that AKINβγ associates through homomeric interactions mediated by both, the γ- and, unexpectedly, the KIS/CBM domain.

Structured summary

MINT-7040005: AKIN (uniprotkb:B4FX20) and AKIN (uniprotkb:B4FX20) physically interact (MI:0914) by chromatography technologies (MI:0091)MINT-7039992: AKIN (uniprotkb:B4FX20) and AKIN (uniprotkb:B4FX20) physically interact (MI:0915) by bimolecular fluorescence complementation (MI:0809)MINT-7040024, MINT-7040044, MINT-7040067: AKIN (uniprotkb:B4FX20) and AKIN (uniprotkb:B4FX20) bind (MI:0407) by pull down (MI:0096)MINT-7039978: SnRK1 (uniprotkb:Q8H1L5) and AKIN (uniprotkb:B4FX20) physically interact (MI:0915) by bimolecular fluorescence complementation (MI:0809)