Characterization of a Strain of Turnip vein-clearing virus Causing Red Ringspot of Penstemon.

A disease of penstemon (Penstemon digitalis) occurring in commercial nurseries in Minnesota in 2004 to 2006 and characterized by red foliar ringspots, leaf deformation, and plant stunting was found to be caused by a strain of Turnip vein-clearing virus (TVCV) that was named Penstemon ringspot virus (PenRSV). This is the first report of a viral disease of penstemon. The genome organization of PenRSV was similar to that of the crucifer-infecting tobamoviruses. The nucleotide sequence of PenRSV was almost identical (99%) to that of TVCV, but the two viruses differed importantly in host range and symptoms induced. The only sequence difference between PenRSV and TVCV occurred at the 3' end of open reading frame I, where the amino acid sequence FRDSNL in TVCV is replaced by FRGQQL in PenRSV. The experimental host range of PenRSV included species in the families Brassicaceae (Cruciferae), Cactaceae, Cucurbitaceae, Leguminosae, Malvaceae, and Solanaceae. This virus poses a potential threat to commercial nursery and bedding plant production because of its wide host range and because it will escape detection by immunoenzymatic screening procedures for tobamoviruses based on use of antibodies to Tobacco mosaic virus (TMV).

Phylogeography of Ustilago maydis virus H1 in the USA and Mexico.

Ustilago maydis virus H1 (Umv-H1) is a mycovirus that infects Ustilago maydis, a fungal pathogen of maize. As Zea mays was domesticated, it carried with it many associated symbionts, such that the subsequent range expansion and cultivation of maize should have affected maize symbionts' evolutionary history dramatically. Because transmission of Umv-H1 takes place only through cytoplasmic fusion during mating of U. maydis individuals, the population dynamics of U. maydis and maize are expected to affect the population structure of the viral symbiont strongly. Here, the impact of changes in the evolutionary history of U. maydis on that of Umv-H1 was investigated. The high mutation rate of this virus allows inferences to be made about the evolution and divergence of Umv-H1 lineages as a result of the recent changes in U. maydis geographical and genetic structure. The phylogeographical history and genetic structure of Umv-H1 populations in the USA and Mexico were determined by using analyses of viral nucleotide sequence variation. Infection and recombination frequencies, genetic diversity and rates of neutral evolution were also assessed, to make inferences regarding evolutionary processes underlying the population genetic structure of ancestral and descendent populations. The results suggest that Mexico represents the ancestral population of Umv-H1, from which the virus has been carried with U. maydis populations into the USA. Thus, the population dynamics of one symbiont represent a major evolutionary force on the co-evolutionary dynamics of symbiotic partners.

Syntheses and characterization of titanium(IV) and titanium(III) complexes with (2-dimethylphosphino)ethane-1-thiolate and (3-dimethylphosphino)propane-1-thiolate as ligands.

Reactions of Cp(2)TiCl(2) (Cp = eta(5)-cyclopentadienide) with 2 or 1 equiv of hybrid P-S ligands (L), (CH(3))(2)P(CH(2))(n)()S(-) (n = 2, dmpet; n = 3, dmppt), produced new dicyclopentadienyltitanium(IV) complexes with L, Cp(2)Ti(L-kappaS)(2) (1, L = dmpet; 2, L = dmppt) and [Cp(2)Ti(L-kappa(2)S,P)]BPh(4) (3, L = dmpet; 4, L = dmppt). The Ti(III) complexes, Cp(2)Ti(L-kappa(2)S,P) (5, L = dmpet; 6, L = dmppt), were prepared by the reaction of Cp(2)Ti(eta(3)-C(3)H(5)) with 1 equiv of L. The structures of complexes 1-6 were confirmed by X-ray diffraction analyses. It was found that complexes 3 and 5 were isostructural around Ti(IV) and Ti(III) centers: the Ti(IV)-S bond length in 3 (2.3498(9) A) is shorter by 0.14 A than Ti(III)-S in 5 (2.4877(7) A), while Ti(IV)-P (2.534(1) A) was merely 0.05 A shorter than Ti(III)-P (2.5844(7) A). The redox potential between 3 and 5 in acetonitrile was -1.14 V vs the ferricinium/ferrocene couple. A heterobimetallic complex that has the frame of complex 1, [Cp(2)Ti(dmpet)(2)Cu]PF(6) (7), was also isolated and structurally characterized: the Ti-Cu distance (2.95(1) A) was shorter than that in [Cp(2)Ti(SC(2)H(4)PPh(2))(2)Cu]BF(4), previously reported by White and Stephan. Structural characterization was also carried out for CpTi(dmpet-kappaS)(2)(dmpet-kappa(2)S,P) (8) and CpTiCl(2)(dmppt-kappa(2)S,P) (9), which were obtained by the reactions of Cp(or Cp)TiCl(3) (Cp = eta(5)-C(5)Me(5)(-)) with n equiv (n = 1-3) of L. The mutual site-exchange reaction between phosphorus atoms on a coordinated dmpet in the kappa(2)S,P mode and on two other coordinated dmpet's in the kappaS mode within complex 8 was analyzed by the variable-temperature (31)P[(1)H] dynamic NMR method. The kinetic parameters for this process, k(ex)(298) = 1.9 x 10(5) s(-)(1), DeltaH = 48 kJ mol(-)(1), and DeltaS = 17 J mol(-)(1) K(-)(1), as well as the rather long Ti(IV)-P distance (2.652(1) A), indicate the fluxional nature of the coordination geometry in complex 8.