Form and function of fungal and oomycete effectors

Plants are able to recognize conserved features of potential microbial invaders and mount an active defense in most cases. Over the course of evolution, a number of these microbes including plant pathogenic fungi and oomycetes have evolved means through the secretion of small molecules (effectors) to block these defenses and promote virulence. In recent years, research has uncovered a wealth of knowledge regarding how effectors function within the plant cell to promote disease. Function of effectors ranges from altering plant cellular metabolic pathways and signaling cascades, RNA silencing, anti-microbial inhibition, and interfering with recognition machinery. The importance of understanding effector function has given rise to a new area of research termed effectoromics, which in this review refers to high-throughput studies to elucidate the function of a large number of candidate effector genes. Effectoromics research has led to the identification of a number of effectors with redundant function, indicating that pathogenic fungi and oomycetes contain effectors that are individually dispensable but functionally redundant that act synergistically to promote disease.