Common and contrasting themes in host cell-targeted effectors from bacterial, fungal, oomycete and nematode plant symbionts described using the Gene Ontology

Abstract

A wide diversity of plant-associated symbionts, including microbes, produce proteins that can enter host cells, or are injected into host cells in order to modify the physiology of the host to promote colonization. These molecules, termed effectors, commonly target the host defense signaling pathways in order to suppress the defense response. Others target the gene expression machinery or trigger specific modifications to host morphology or physiology that promote the nutrition and proliferation of the symbiont. When recognized by the host's surveillance machinery, which includes cognate resistance (R) gene products, defense responses are engaged to restrict pathogen proliferation. Effectors from diverse symbionts may be delivered into plant cells via varied mechanisms, including whole organism cellular entry (viruses, some bacteria and fungi), type III and IV secretion (in bacteria), physical injection (nematodes and insects) and protein translocation signal sequences (oomycetes and fungi). This mini-review will summarize both similarities and differences in effectors and effector delivery systems found in diverse plant-associated symbionts as well as how these are described with Plant-Associated Microbe Gene Ontology (PAMGO) terms.

Transcriptional Programming and Functional Interactions within the Phytophthora sojae RXLR Effector Repertoire

“…Effector proteins are secreted by many plant pathogens to promote infection Chang et al, 2004;Gö hre and Robatzek, 2008;Torto-Alalibo et al, 2009). Gramnegative bacterial plant pathogens, such as Pseudomonas syringae, Ralstonia solanacearum, and Xanthomonas campestris, deliver 15 to 30 effectors per strain into host cells using type III secretion systems to suppress PTI and ETI, including the HR (Kjemtrup et al, 2000).…”

Unifying Themes in Microbial Associations with Animal and Plant Hosts Described Using the Gene Ontology

“…In plant-parasitic nematodes, secretions are synthesized in the esophageal subventral and dorsal glands and released directly into the host cell via a hollow spear-like structure, the stylet. The direct injection of secretions via the stylet, which includes effectors (also called parasitism proteins), is analogous to the injection of bacterial effectors via the T3SS injectisome (29,208). The stylet also serves as a feeding structure, withdrawing nutrients from the host cytoplasm (195).…”

“…In the GO database, effectors that target signal transduction in the host are generally annotated with the term "GO:0052027 modulation by symbiont of host signal transduction pathway" (208). In some cases, the effector and target have been more extensively characterized, supporting annotation with more-specific child terms.…”

“…Secretions from the stylet can transform root cells in susceptible plants into metabolically active feeding cells, a process that can be described with "GO:0044005 induction by symbiont in host of tumor, nodule, or growth" (208,222). Analogous to terms used to describe other mechanisms of effector delivery discussed above, "GO:0085003 interaction with host via secreted substance released from stylet" is an appropriate term to describe the mechanism of effector delivery into host cells via the stylet (29,208).…”

“…Although the PAMGO consortium's focus was initially intended to be plant hosts, it quickly became evident that all but the most specific terms were also useful in the context of animal hosts as well. The PAMGO initiative has so far created over 900 terms (28,122,134,208). Changes are constantly made to the GO database, and new terms are added as knowledge accrues.…”