When host defense is clearly implicated, for example when PCD is triggered by the detection of a pathogen MAMP by a hostR-gene product, it would be appropriate to use the
GO term “”GO: 0034055 positive regulation by symbiont of host defense-related programmed cell death”" (Figure2). An example of this is a family of extracellular proteins called elicitins that are secreted by manyPhytophthoraspecies and that trigger localized cell death inNicotianahost plant species . The response ofNicotiana benthamianato the elicitin INF1 prevents infection byPhytophthora infestans. In this particular interaction, even though the triggering of PCD in the host is detrimental to Tariquidar supplier the pathogen, it nevertheless reflects one action of the pathogen proteinin planta. This underscores the notion that the purpose of GO terms is to describe biological
processes, irrespective of whether see more the outcome of a process is subjectively judged to be beneficial or detrimental. Manipulation of PCD by diverse symbionts Because PCD is a central mechanism of defense used by both animals and plants against microbes, manipulation by the symbiont of host PCD is central to many strategies by which symbionts neutralize host defenses. The following sections summarize some different strategies employed by symbionts for manipulation of host PCD. In these sections, we use the word “”effector”" to indicate symbiont gene products that influence the physiology or morphology of the host in order to promote colonization. Many effectors are proteins that modulate host defenses, selleck kinase inhibitor including PCD (reviewed in [18,36,37]), and many of these are translocated into the cytoplasm of host cells [18,36,37]. In the context of plant defenses, mostR-gene products detect symbiont effector proteins [18,36–38]. Historically, genes encoding effectors recognized byR-genes have been called “”avirulence genes”" . Viruses and PCD In accord with the requirements of the different stages of viral replication in living cells, viruses
both inhibit and induce apoptosis in host cells; this has been extensively studied in animal systems (reviewed in ). The suppression of host apoptosis by viruses is PtdIns(3,4)P2 a critical aspect of prolonging cell survival during viral replication, which is captured in the GO by the term “”GO: 0019050 suppression by virus of host apoptosis”", a child term of “”GO: 0052041 negative regulation by symbiont of host programmed cell death”" (both shown in Figure2) . Suppression of the host immune response by inhibiting apoptosis is accomplished by viruses and viral proteins through targeting of host PCD signalling pathways . As a normal part of the infection cycle of many viruses, the release and spread of progeny virions is accomplished by lysis of the host cell.