During 35 months of selective in vitro cultivation, Neisseria gonorrhoeae cells retained their virulence for humans and were shown to be closely related to a particular colonial morphology. Saline-autoagglutinability was the only other characteristic distinguishing virulent from avirulent cells. Human responses to challenge with cells of the different colonial types were studied for their relat...

Virulence and avirulence genes carried on large, unstable pathogenicity islands (PAI) strongly influence the course and fate of host-pathogen interactions. A recent study shows how one such PAI can be rapidly transferred between two closely related bacteria via transformation in vivo, and how this horizontal gene transfer affects the fitness of the recipient strain.

In the gene-for-gene hypothesis, Flor [19] proposed the existence of avirulence alleles of virulence genes, and that the virulence genes actively conditioned cultivar-specific virulence on hosts. Yet cultivar-specific virulence genes have not been found, and many of the avirulence (aŠr) genes cloned to date (over 40) do not appear to condition pathogenicity in general, virulence or anything els...

(2006) Spatial and temporal expression patterns of Avr1b-1 and defense-related genes in soybean plants upon infection with Phytophthora sojae. 1 Introduction 1 1. 1 P l a n t r e s i s t a n c e 1 1.2 Signal transduction 2

Xanthomonas oryzae pv. oryzae (Xoo) Philippine race 6 (PR6) is unable to cause bacterial blight disease on rice lines containing the rice resistance gene Xa21 but is virulent on non-Xa21 rice lines, indicating that PR6 carries avirulence (avrXa21) determinants required for recognition by XA21. Here we show that two Xoo genes, raxP and raxQ, are required for AvrXa21 activity. raxP and raxQ, whic...

Wheat leaf rust, caused by the basidiomycete Puccinia triticina, can cause yield losses of up to 20% in wheat producing regions. During infection, the fungus forms haustoria that secrete proteins into the plant cell and effect changes in plant transcription, metabolism, and defense. It is hypothesized that new races emerge as a result of overcoming plant resistance via changes in the secreted e...