No abstract

An epigenetic control of vernalization has been demonstrated in annual plants such as Arabidopsis and cereals, but the situation remains unclear in biennial plants such as sugar beet that has an absolute requirement for vernalization. The role of DNA methylation in flowering induction and the identification of corresponding target loci also need to be clarified. In this context, sugar beet (Beta vulgaris altissima) genotypes differing in bolting tolerance were submitted to various bolting conditions such as different temperatures and/or methylating drugs. DNA hypomethylating treatment was not sufficient to induce bolting while DNA hypermethylation treatment inhibits and delays bolting. Vernalizing and devernalizing temperatures were shown to affect bolting as well as DNA methylation levels in the shoot apical meristem. In addition, a negative correlation was established between bolting and DNA methylation. Genotypes considered as resistant or sensitive to bolting could also be distinguished by their DNA methylation levels. Finally, sugar beet homologues of the Arabidopsis vernalization genes FLC and VIN3 exhibited distinct DNA methylation marks during vernalization independently to the variations of global DNA methylation. These vernalization genes also displayed differences in mRNA accumulation and methylation profiles between genotypes resistant or sensitive to bolting. Taken together, the data suggest that the time course and amplitude of DNA methylation variations are critical points for the induction of sugar beet bolting and represent an epigenetic component of the genotypic bolting tolerance, opening up new perspectives for sugar beet breeding.

In sugarbeet (Beta vulgaris subsp. vulgaris), many linkage maps have been constructed, but the availability of markers continues to limit utility of genetic maps in public domain programs. Here a framework genetic map is presented that is expandable and transferable to research programs interested in locating their markers on a consensus map. In its current framework, the primary markers used were amplified fragment length polymorphisms (AFLPs) that were anchored to Butterfass chromosome‐nomenclature linkage groups using linkage group specific markers validated in other populations. Thus, a common framework has been established that anchors 331 markers, including 23 newly mapped simple sequence repeat (SSR) markers, having a combined total of 526.3 cM among the nine beet linkage groups. The source of the mapping population was a sugarbeet × table beet population, and this is the first report of a map constructed with a relatively wide cross in B. vulgaris Segregation distortion was common (22% of loci), particularly extreme for Butterfass Chromosome 5, and predominantly favored the sugarbeet (seed parent) allele. Physical segments of the beet genome that carry mapped markers have been identified, demonstrating that physical and genetic mapping are facile and complementary applications for beet improvement.

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f Macrophage infectivity potentiators (Mips) are immunophilin proteins and essential virulence factors for a range of pathogenic organisms. We applied a structural biology approach to characterize a Mip from Burkholderia pseudomallei (BpML1), the causative agent of melioidosis. Crystal structure and nuclear magnetic resonance analyses of BpML1 in complex with known macrocyclics and other derivatives led to the identification of a key chemical scaffold. This scaffold possesses inhibitory potency for BpML1 without the immunosuppressive components of related macrocyclic agents. Biophysical characterization of a compound series with this scaffold allowed binding site specificity in solution and potency determinations for rank ordering the set. The best compounds in this series possessed a low-micromolar affinity for BpML1, bound at the site of enzymatic activity, and inhibited a panel of homologous Mip proteins from other pathogenic bacteria, without demonstrating toxicity in human macrophages. Importantly, the in vitro activity of BpML1 was reduced by these compounds, leading to decreased macrophage infectivity and intracellular growth of Burkholderia pseudomallei. These compounds offer the potential for activity against a new class of antimicrobial targets and present the utility of a structure-based approach for novel antimicrobial drug discovery.