Oomycete intracellular effectors: specialized weapons targeting strategic plant processes.

Oomycete phytopathogens have adapted to colonize plants by using effectors as their molecular weapons. Intracellular effectors, mostly proteins but also small ribonucleic acids, are delivered by the pathogens into the host cell cytoplasm where they interfere with normal plant physiology. The diverse host processes emerging as "victims" of these "specialized bullets" include gene transcription and RNA-mediated silencing, cell death, protein stability, protein secretion, and autophagy. Some effector targets are directly involved in defense execution, while others participate in fundamental metabolisms whose alteration collaterally affects defenses. Other effector targets are susceptibility factors (SFs), i.e., host components that make plants vulnerable to pathogens. SFs are mostly negative regulators of immunity, but some seem necessary to sustain or promote pathogen colonization.