An insight into the genetic polymorphism among European populations of Lactuca serriola assessed by AFLP

Prickly lettuce (Lactuca serriola) is world-wide distributed and very variable species generally considered as a progenitor of the cultivated lettuce (Lactuca sativa). Altogether, 50 populations of L. serriola were characterized by means of amplified fragment length polymorphism (AFLP) and by isozyme analysis. Relationships among individuals and populations were examined by applying the unweighted pair-group method with the arithmetic averages (UPGMA) clustering algorithm, principal coordinate analysis (PCA) and the Nei's gene diversity index. The studied set of populations split into three main groups based on the AFLP polymorphism analysis. The first group contained L. sativa (control). The second group comprised two L. serriola accessions; one of them was identified as L. serriola f. integrifolia and the other as a mixture of two L. serriola forms. The largest and the most diverse third group contained the remaining L. serriola accessions. The population clustering corresponded approximately to their geographical distribution in Europe. At least five distinct geographic groups were recognised: 1) Northern European; 2) Slovenian; 3) very heterogeneous Central and Western European (mostly north of the Alps); 4) Mediterranean; 5) prevalence of L. serriola f. integrifolia, mostly comprising accessions from the United Kingdom and the Netherlands. This study showed that accessions originating in various eco-geographical conditions of Europe differ significantly in their genetic and protein polymorphism, as well as in morphology. Some European L. serriola populations (e.g. from Scandinavia and United Kingdom/British Isles/) seems to be isolated and homogeneous; in contrast, populations occurring in Central Europe are very diverse and genetically overlapping.     

The structural plasticity of SCA7 domains defines their differential nucleosome‐binding properties

SAGA (Spt–Ada–Gcn5 acetyltransferase), a coactivator complex involved in chromatin remodelling, harbours both histone acetylation and deubiquitination activities. ATXN7/Sgf73 and ATXN7L3, two subunits of the SAGA deubiquitination module, contain an SCA7 domain characterized by an atypical zinc‐finger. We show that the yeast Sgf73–SCA7 domain is not required to recruit Sgf73 into SAGA. Instead, it binds to nucleosomes, a property that is conserved in the human ATXN7–SCA7 domain but is lost in the ATXN7L3 domain. The solution structures of the SCA7 domain of both ATXN7 and ATXN7L3 reveal a new, common zinc‐finger motif at the heart of two distinct folds, providing a molecular basis for the observed functional differences.     

Calcium channel structural determinants of synaptic transmission between identified invertebrate neurons

We report here that unlike what was suggested for many vertebrate neurons, synaptic transmission in Lymnaea stagnalis occurs independent of a physical interaction between presynaptic calcium channels and a functional complement of SNARE proteins. Instead, synaptic transmission in Lymnaea requires the expression of a C-terminal splice variant of the Lymnaea homolog to mammalian N- and P/Q-type calcium channels. We show that the alternately spliced region physically interacts with the scaffolding proteins Mint1 and CASK, and that synaptic transmission is abolished following RNA interference knockdown of CASK or after the injection of peptide sequences designed to disrupt the calcium channel-Mint1 interactions. Our data suggest that Mint1 and CASK may serve to localize the non-L-type channels at the active zone and that synaptic transmission in invertebrate neurons utilizes a mechanism for optimizing calcium entry, which occurs independently of a physical association between calcium channels and SNARE proteins.     

Intracellularly expressed single-domain antibody against p15 matrix protein prevents the production of porcine retroviruses

The presence of porcine endogenous retroviruses presents a potential risk of transmission of infectious diseases (xenozoonosis) if tissues and organs from genetically modified pigs are to be used in xenotransplantation. Here, we report that intracellular expression of a llama single-domain antibody against p15, the matrix domain protein of the porcine endogenous retrovirus Gag polyprotein, blocks retrovirus production, providing the possibility of eliminating the risk of infection in xenotransplantation.     

QTLs for tomato powdery mildew resistance (Oidium lycopersici) in Lycopersicon parviflorum G1.1601 co-localize with two qualitative powdery mildew resistance genes

Tomato (Lycopersicon esculentum) is susceptible to the powdery mildew Oidium lycopersici, but several wild relatives such as Lycopersicon parviflorum G1.1601 are completely resistant. An F2 population from a cross of Lycopersicon esculentum cv. Moneymaker x Lycopersicon parviflorum G1.1601 was used to map the O. lycopersici resistance by using amplified fragment length polymorphism markers. The resistance was controlled by three quantitative trait loci (QTLs). Ol-qtl1 is on chromosome 6 in the same region as the Ol-1 locus, which is involved in a hypersensitive resistance response to O. lycopersici. Ol-qtl2 and Ol-qtl3 are located on chromosome 12, separated by 25 cM, in the vicinity of the Lv locus conferring resistance to another powdery mildew species, Leveillula taurica. The three QTLs, jointly explaining 68% of the phenotypic variation, were confirmed by testing F3 progenies. A set of polymerase chain reaction-based cleaved amplified polymorphic sequence and sequence characterized amplified region markers was generated for efficient monitoring of the target QTL genomic regions in marker assisted selection. The possible relationship between genes underlying major and partial resistance for tomato powdery mildew is discussed.     

Engineering the mouse genome with bacterial artificial chromosomes to create multipurpose alleles

The mouse is the leading vertebrate model because its genome can be altered by both random transgenesis and homologous recombination with targeting constructs. Both approaches have been hindered by the size and site limitations implicit in conventional Escherichia coli DNA-engineering methods. Homologous recombination in E. coli, or 'recombineering', has overcome these limitations for bacterial artificial chromosome (BAC) transgenesis. Here we applied Red/ET recombineering (using the lambda Redalpha/Redbeta recombinase pair) to generate a 64 kilobase targeting construct that carried two selectable cassettes permitting the simultaneous mutation of the target gene, Mll, at sites 43 kb apart in one round of mouse embryonic stem (ES) cell targeting. The targeting frequency after dual selection was 6%. Because the two selectable cassettes were flanked by FRT or loxP sites, three more alleles can be generated by site-specific recombination. Our approach represents a simple way to introduce changes at two or more sites in a genetic locus, and thereafter generate allele combinations. The size of BAC templates offers new freedom for the design of targeting constructs. Combined with the use of two selectable cassettes placed far apart, BAC-based targeting constructs may be applicable to tasks such as regional exchanges, deletions, and insertions.     

Long-range physical maps of two loci (Aps-1 and GP79) flanking the root-knot nematode resistance gene (Mi) near the centromere of tomato chromosome 6

The root knot nematode resistance gene Mi in tomato has been mapped in the pericentromeric region of chromosome 6. With the objective of isolating Mi through a map-based cloning approach, we have previously identified and ordered into a high-resolution genetic linkage map a variety of tightly linked molecular markers. Using pulsed-field gelelectrophoresis and various rarely cutting restriction enzymes in single, double and partial digestions, we now report long-range physical maps of the two closest flanking markers, acid phosphatase-1 (Aps-1) and GP79, which span over 400 and 800 kb, respectively. It is concluded that the physical distance between both markers is larger than predicted on the basis of genetic linkage analysis. Furthermore, two RFLP markers (H3F8 and H4H10) which map genetically to the same locus as Aps-1 do not show physical linkage, indicating severe suppression of recombination in this region of the chromosome. Finally, no evidence was obtained showing the presence of a CpG island near Aps-1.