Quantitative and Qualitative Stem Rust Resistance Factors in Barley Are Associated with Transcriptional Suppression of Defense Regulons

Stem rust (Puccinia graminis f. sp. tritici; Pgt) is a devastating fungal disease of wheat and barley. Pgt race TTKSK (isolate Ug99) is a serious threat to these Triticeae grain crops because resistance is rare. In barley, the complex Rpg-TTKSK locus on chromosome 5H is presently the only known source of qualitative resistance to this aggressive Pgt race. Segregation for resistance observed on seedlings of the Q21861 × SM89010 (QSM) doubled-haploid (DH) population was found to be predominantly qualitative, with little of the remaining variance explained by loci other than Rpg-TTKSK. In contrast, analysis of adult QSM DH plants infected by field inoculum of Pgt race TTKSK in Njoro, Kenya, revealed several additional quantitative trait loci that contribute to resistance. To molecularly characterize these loci, Barley1 GeneChips were used to measure the expression of 22,792 genes in the QSM population after inoculation with Pgt race TTKSK or mock-inoculation. Comparison of expression Quantitative Trait Loci (eQTL) between treatments revealed an inoculation-dependent expression polymorphism implicating Actin depolymerizing factor3 (within the Rpg-TTKSK locus) as a candidate susceptibility gene. In parallel, we identified a chromosome 2H trans-eQTL hotspot that co-segregates with an enhancer of Rpg-TTKSK-mediated, adult plant resistance discovered through the Njoro field trials. Our genome-wide eQTL studies demonstrate that transcript accumulation of 25% of barley genes is altered following challenge by Pgt race TTKSK, but that few of these genes are regulated by the qualitative Rpg-TTKSK on chromosome 5H. It is instead the chromosome 2H trans-eQTL hotspot that orchestrates the largest inoculation-specific responses, where enhanced resistance is associated with transcriptional suppression of hundreds of genes scattered throughout the genome. Hence, the present study associates the early suppression of genes expressed in this host–pathogen interaction with enhancement of R-gene mediated resistance

Deformability of poly(amidoamine) dendrimers

Experimental data indicates that poly(amidoamine) (PAMAM) dendrimers flatten when in contact with a substrate, i.e. they are no longer spherical, but resemble flat disks. In order to better understand the deformation behavior of these branched polymers, a series of atomistic molecular dynamics simulations is performed. The resulting flattened dendrimer conformations are compared to atomic force microscopy (AFM) images of individual dendrimers at air/mica and water/mica interfaces. The ability of the polymers to deform is investigated as a function of dendrimer generation (2-5) and the required energies are calculated. Our modeling results show good agreement with the experimental AFM images, namely that dendrimers are highly flexible and capable of forming multiple interaction sites between most of their branch ends and the substrate. The deformation energy scales with dendrimer generation and does not indicate an increase in stiffness between generations 2 and 5 due to steric effects.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45831/1/10189_2003_Article_10087.pd

Characterisation of Phaseolus symbionts isolated from Mediterranean soils and analysis of genetic factors related to pH tolerance

Priefer UB, Aurag J, Boesten B, et al. Characterisation of Phaseolus symbionts isolated from Mediterranean soils and analysis of genetic factors related to pH tolerance. J Biotechnol. 2001;91(2-3):223-236.The ultimate objective of PhIMED, in which two European (Germany, Italy) and two Mediterranean (Morocco, Egypt) countries collaborate, is to improve the cultivation of French bean (Phaseolus vulgaris) under arid and semi-arid conditions by analysing and enhancing stress tolerance of the nitrogen fixing rhizobial microsymbionts. Rhizobial strains nodulating P. vulgaris (RP strains) isolated from areas in Morocco frequently subjected to drought were analysed for their salt and pH tolerance and their phylogenetic relationship. Strain RP163, exhibiting high nodulation efficiency and a broad pH tolerance was mutagenised by Tn5 and mutants unable to grow on extreme pH media were isolated. Some of the mutants affected in low pH tolerance were found to be mutated in genes related to cobalmin biosynthesis and in succinate dehydrogenase (sdhA). In a parallel approach, promoters and genes inducible under extreme pH values were identified in Rhizobium leguminosarum bv. viciae VF39, among them gabT, which encodes the GABA transaminase and which is induced under acidic conditions. The same gene is present and similarly regulated in RP163. The actSR gene region was cloned from VF39, sequenced and mutants generated in this region were found to be impaired in growth at low pH, but also under neutral conditions. The Agrobacterium rhizogenes 'promintron' promoter, reported to be activated in stationary phase, was found to be also strongly induced under acidic conditions in rhizobia and it is currently being characterised to construct a system allowing the expression of stress tolerance genes in bacteroids and free-living bacteria

Molecular modelling of the interactions of carbamazepine and a nicotinic receptor involved in the autosomal dominant nocturnal frontal lobe epilepsy

1. The normal and a mutant (S248F) human neuronal α4β2 nicotinic receptors, and their interaction with the channel blocker carbamazepine (CBZ) have been modelled. The mutant, responsible for the autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE), has an enhanced sensitivity to and a slower recovery from desensitization, a lower conductance, short open times, reduced calcium permeability, and is 3 fold more sensitive to CBZ, a drug used in the treatment of partial epilepsies. 2. Mutant channel properties are explained by the physicochemical properties of the two Phe248 side chains, including size and cation-π interaction, and their dynamic behaviour. A defective mechanism of dehydration might be responsible for the reduced calcium influx. 3. Phe248 residues are the main component of CBZ binding sites in the mutant, while this is not true for Ser248 in the normal receptor. 4. A higher number of blocking binding sites and a predicted higher affinity found for CBZ in the mutant account for its differential sensitivity to CBZ. 5. Aromatic–aromatic interactions between CBZ and the two Phe248 account for the difference in affinity, which is at least 12 times higher for the mutant, depending on the method used for calculating K(i). 6. Normal vs mutant differences in K(i), enhanced by the higher number of blocking binding sites in the mutant, seem excessive compared to the differential sensitivities to CBZ experimentally found. The negative cooperativity suggested by a predicted overlapping of blocking and non-blocking binding sites gives an explanation, as overlapping is higher in the mutant. 7. For both types of receptors we found that the carbamyl group of the best blocking conformers of CBZ forms hydrogen bonds with serine residues, which may explain the fundamental role of that moiety for this molecule to act as antiepileptic drug