, 2009), and high levels of ABA have

been shown to alter plant susceptibility to infection (de Torres-Zabala et al., 2007; Goel et al., 2008). It has been shown in some interactions that the bacterium itself produces ROS that contribute to pathogenicity. For example, Mahajan-Miklos et al. (1999) identified a gene in the opportunistic pathogen, P. aeruginosa PA14, which is essential for fast killing of the nematode, Caenorhabditis elegans, and is also involved in pathogenicity on Arabidopsis. This gene encodes a phenazine toxin, pyocyanin, which leads to the production of superoxide and hydrogen peroxide under aerobic conditions (Mahajan-Miklos et al., 1999). The authors were able to provide evidence that Talazoparib purchase ROS production was important find more for the pathogenicity effect. More recently, it has been shown that pyocyanin produced by P. aeruginosa directly inactivates catalase in the human lung epithelium via superoxide production (O’Malley et al., 2003) and that the ROS produced by pyocyanin in human cells can inactivate vacuolar ATPase (Ran et al., 2003). Given the overlap between genes involved in pathogenicity of P. aeruginosa on Arabidopsis and other hosts (Mahajan-Miklos et al., 1999), it seems likely that similar mechanisms may also be important in planta. It is clear that ROS play a key role in plant–pathogen interactions; they are used by plants as a weapon against pathogens

via direct toxicity and are important effectors in bacterial cell death mechanisms. Successful pathogens must therefore be able to tolerate this threat. But plants also use ROS in signalling, which bacteria may be able to manipulate for their own Epothilone B (EPO906, Patupilone) ends or to downregulate to avoid further defence responses. In a final twist, it appears that some Pseudomonas pathogens may even use

ROS as a pathogenicity or virulence factor during interactions with plants. A summary of the ways in which various groups of Pseudomonads interact with ROS is given in Table 1. Further work is needed to fully illuminate a number of the areas covered in this review. For instance, the role of PHAs in ROS tolerance remains opaque. Similarly, more insight could be sought into the ways in which plant pathogenic Pseudomonads manipulate plant ROS homeostasis, and the importance of this manipulation for pathogenesis. There is yet to be a full understanding of the consequences of the changes observed in infected plants in this complex and dynamic process. Recent developments such as the demonstration of the connection between HopG1a and ROS production indicate the potential for research in this area to improve our understanding of plant–pathogen interactions. “
“We present draft genome sequences of three Holospora species, hosted by the ciliate Paramecium caudatum; that is, the macronucleus-specific H. obtusa and the micronucleus-specific H. undulata and H. elegans.