Gene expression analysis of Salmonella enterica SPI in macrophages indicates differences between serovars that induce systemic disease from those normally causing enteritis.

Global gene expression of the invasive Salmonella serovars S. Enteritidis and S. Typhimurium, and the less-invasive S. Infantis and S. Hadar was studied during infection of a chicken macrophage cell line. Major functional gene groups responsible for intracellular physiological changes were regulated similarly in all four serovars. However, SPI1 and SPI4 genes of S. Enteritidis and S. Typhimurium were strongly repressed in the macrophages whereas S. Infantis, S. Hadar and other similar serovars maintained up-regulation of these gene sets. This phenomenon may explain some of the biological differences between invasive and non-invasive Salmonella serovars.

The role of the coat protein region in symptom formation on Physalis floridana varies between PVY strains.

The Potato virus Y (PVY) cDNA full-length clone created by Jakab et al. [Jakab, G., Droz, E., Brigneti, G., Baulcombe, D., Malnoë, P., 1997. Infectious in vivo and in vitro transcripts from a full-length cDNA clone of PVY-N605, a Swiss necrotic isolate of potato virus Y. J. Gen. Virol. 78, 3141-3145] was stabilized by inserting three introns into putatively toxic genes. Using this clone, hybrid viruses were constructed by in vitro recombination. The PVY-N/NTN and PVY-N/O chimeras carried the 3' end of NIb, the whole CP and 3'UTR region of PVY(NTN) and PVY(O), respectively, in a PVY(N) genetic background. The clones proved to be stable after several passages by re-sequencing the exchanged region. Both hybrid viruses showed reduced infectivity in particle bombardment experiments, but they were suitable for further mechanical plant inoculation. In five of the six host plant species, inoculated with the two chimeras and three parental strains, the chimeras produced similar symptoms to those of PVY(N). By contrast, Physalis floridana reacted with different pattern of symptoms. In this species, the symptoms caused by the N/O hybrid were similar to those of the 3'NIb-CP-donating PVY(O) strain, and not to those of the background (PVY(N)). The results suggest that symptom determinants may be different even between strains of the same virus species in a particular host.

Engineering resistance to PVY in different potato cultivars in a marker-free transformation system using a 'shooter mutant' A. tumefaciens.

In this work, Potato virus Y (PVY) resistant potatoes were generated using an environmentally safe construct. For this purpose, a 'shooter' mutant Agrobacterium-based transformation system was used. The isopentenyl transferase gene (ipt) present on the Ti plasmid of 'shooter' strains enhances shoot regeneration and can be used as a phenotypic selection marker. The introduced marker-free binary vector carried a hairpin construct derived from the coat protein gene of PVY-NTN strain in order to induce gene silencing. Transformation resulted in high regeneration rates (1.4-5.7 shoots per explant). With pre-selection for the ipt (+) phenotype the transformation frequency was 24-53%, while without selection 12-28% of the shoots were PCR positive. The presence of the transgene was verified by Southern hybridization. In 16 of 31 challenged transformant lines PVY could be detected neither by RT-PCR nor by back inoculation. A 62.5% of these resistant lines proved to be also ipt-free. This transformation system was reproducible in four potato cultivars, suggesting that it could easily be adapted for other species.