The wheat durable,multipathogen resistance gene Lr34 confers partial blast resistance in rice

The wheat gene Lr34 confers durable and partial field resistance against the obligate biotrophic, pathogenic rust fungi and powdery mildew in adult wheat plants. The resistant Lr34 allele evolved after wheat domestication through two gain‐of‐function mutations in an ATP‐binding cassette transporter gene. An Lr34‐like fungal disease resistance with a similar broad‐spectrum specificity and durability has not been described in other cereals. Here, we transformed the resistant Lr34 allele into the japonica rice cultivar Nipponbare. Transgenic rice plants expressing Lr34 showed increased resistance against multiple isolates of the hemibiotrophic pathogen Magnaporthe oryzae, the causal agent of rice blast disease. Host cell invasion during the biotrophic growth phase of rice blast was delayed in Lr34‐expressing rice plants, resulting in smaller necrotic lesions on leaves. Lines with Lr34 also developed a typical, senescence‐based leaf tip necrosis (LTN) phenotype. Development of LTN during early seedling growth had a negative impact on formation of axillary shoots and spikelets in some transgenic lines. One transgenic line developed LTN only at adult plant stage which was correlated with lower Lr34 expression levels at seedling stage. This line showed normal tiller formation and more importantly, disease resistance in this particular line was not compromised. Interestingly, Lr34 in rice is effective against a hemibiotrophic pathogen with a lifestyle and infection strategy that is different from obligate biotrophic rusts and mildew fungi. Lr34 might therefore be used as a source in rice breeding to improve broad‐spectrum disease resistance against the most devastating fungal disease of rice.     

The physiological basis of seed dormancy in Avena fatua. II. On the involvement of alternative respiration in the stimulation of germination by sodium azide

Chromatography on DEAE-cellulose of an extract from etiolated leaves of sorghum ( Sorghum vulgare Pers. cv. INRA 450), a C₄ plant, gave only one form of phosphoenol pyruvate carboxylase with functional and regulatory properties of a C₃ type plant enzyme. Greening of the leaves resulted in a significant increase in activity. This increase was due to the appearance of a new form of the enzyme, which eluted at lower ionic strength and exhibited new properties. This form was glucose-6-P activated and showed a sigmoidal curve response to the concentration of the substrate phosphoerralpyruvate. These kinetic properties are typical of a C₄ plant enzyme.     

Reciprocal control of flowering time by OsSOC1 in transgenic Arabidopsis and by FLC in transgenic rice

In a screen for MADS box genes which activate and/or repress flowering in rice, we identified a gene encoding a MADS domain protein (OsSOC1) related to the Arabidopsis gene AtSOC1. AtSOC1 and OsSOC1 show a 97% amino acid similarity in their MADS domain. The rice gene contains a large first intron of 27.6 kb compared to the 1 kb intron in Arabidopsis. OsSOC1 is located on top of the short arm of chromosome 3, tightly linked to the heading date locus, Hd9. OsSOC1 is expressed in vegetative tissues, and expression is elevated at the time of floral initiation, 40-50 days after sowing, and remains uniformly high thereafter, similar to the expression pattern of AtSOC1. The constitutive expression of OsSOC1 in Arabidopsis results in early flowering, suggesting that the rice gene is a functional equivalent of AtSOC1. We were not able to identify FLC-like sequences in the rice genome; however, we show that ectopic expression of the Arabidopsis FLC delays flowering in rice, and the up-regulation of OsSOC1 at the onset of flowering initiation is delayed in the AtFLC transgenic lines. The reciprocal recognition and flowering time effects of genes introduced into either Arabidopsis or rice suggest that some components of the flowering pathways may be shared. This points to a potential application in the manipulation of flowering time in cereals using well characterized Arabidopsis genes.     

A survey of soils for aggregate stability and glomalin,a glycoprotein produced by hyphae of arbuscular mycorrhizal fungi

Understanding the contributions of soil microorganisms to soil stabilization at the molecular level will lead to ways to enhance inputs for sustainable agricultural systems. Recent discoveries of copious production of glycoprotein (glomalin) by arbuscular mycorrhizal (AM) fungi and the apparent recalcitrance of this material in soils led to the comparison between concentration of glomalin and aggregate stability. Stability was measured on air-dried aggregates rewetted by capillary action and then subjected to wet sieving for 10 min. Thirty-seven samples from four geographic areas of the U.S. and one area of Scotland were tested. The monoclonal antibody used to discover glomalin on AM hyphae was employed to assess immunoreactive glomalin on aggregate surfaces by immunofluorescence and in extracts from aggregates by enzyme-linked immunosorbent assay (ELISA). Immunofluorescence was observed on at least some surfaces of aggregates from all soils examined, but was most evident on aggregates with high glomalin concentrations. Easily extractable glomalin (EEG) was solubilized by 20 mM citrate, pH 7.0 at 121 °C for 30 min, and total glomalin (TG) was solubilized with 50 mM citrate, pH 8.0 at 121 °C for 90 to 450 min. Some soils required up to seven sequential extractions to remove all of the glomalin. Aggregate stability was linearly correlated (p < 0.001) with all measures of glomalin (mg/g of aggregates) in these soils. The best predictor of aggregate stability (AS) was immunoreactive easily extractable glomalin (IREEG) according to the following relationship: AS = 42.7 +61.3 × log₁₀ IREEG (r₂ = 0.86; p <0.001, n = 37).     

Evolution of Escherichia coli in different carbon environments for 2,000 generations

Cellular energetics is thought to have played a key role in dictating all major evolutionary transitions in the history of life on Earth. However, how exactly cellular energetics and metabolism come together to shape evolutionary paths is not well understood. In particular, when an organism is evolved in different energy environments, what are the phenomenological differences in the chosen evolutionary trajectories, is a question that is not well understood. In this context, starting from an Escherichia coli K‐12 strain, we evolve the bacterium in five different carbon environments—glucose, arabinose, xylose, rhamnose and a mixture of these four sugars (in a predefined ratio) for approximately 2,000 generations. At the end of the adaptation period, we quantify and compare the growth dynamics of the strains in a variety of environments. The evolved strains show no specialized adaptation towards growth in the carbon medium in which they were evolved. Rather, in all environments, the evolved strains exhibited a reduced lag phase and an increased growth rate. Sequencing results reveal that these dynamical properties are not introduced via mutations in the precise loci associated with utilization of the sugar in which the bacterium evolved. These phenotypic changes are rather likely introduced via mutations elsewhere on the genome. Data from our experiments indicate that evolution in a defined environment does not alter hierarchy in mixed‐sugar utilization in bacteria.     

Cytoskeletal forces during signaling activation in Jurkat T-cells

T-cells are critical for the adaptive immune response in the body. The binding of the T-cell receptor (TCR) with antigen on the surface of antigen-presenting cells leads to cell spreading and signaling activation. The underlying mechanism of signaling activation is not completely understood. Although cytoskeletal forces have been implicated in this process, the contribution of different cytoskeletal components and their spatial organization are unknown. Here we use traction force microscopy to measure the forces exerted by Jurkat T-cells during TCR activation. Perturbation experiments reveal that these forces are largely due to actin assembly and dynamics, with myosin contractility contributing to the development of force but not its maintenance. We find that Jurkat T-cells are mechanosensitive, with cytoskeletal forces and signaling dynamics both sensitive to the stiffness of the substrate. Our results delineate the cytoskeletal contributions to interfacial forces exerted by T-cells during activation.     

Rad53 is essential for a mitochondrial DNA inheritance checkpoint regulating G1 to S progression

The Chk2-mediated deoxyribonucleic acid (DNA) damage checkpoint pathway is important for mitochondrial DNA (mtDNA) maintenance. We show in this paper that mtDNA itself affects cell cycle progression. Saccharomyces cerevisiae rho(0) cells, which lack mtDNA, were defective in G1- to S-phase progression. Deletion of subunit Va of cytochrome c oxidase, inhibition of F(1)F(0) adenosine triphosphatase, or replacement of all mtDNA-encoded genes with noncoding DNA did not affect G1- to S-phase progression. Thus, the cell cycle progression defect in rho(0) cells is caused by loss of DNA within mitochondria and not loss of respiratory activity or mtDNA-encoded genes. Rad53p, the yeast Chk2 homologue, was required for inhibition of G1- to S-phase progression in rho(0) cells. Pif1p, a DNA helicase and Rad53p target, underwent Rad53p-dependent phosphorylation in rho(0) cells. Thus, loss of mtDNA activated an established checkpoint kinase that inhibited G1- to S-phase progression. These findings support the existence of a Rad53p-regulated checkpoint that regulates G1- to S-phase progression in response to loss of mtDNA.