Taking the stage: effectors in the spotlight

Abstract

Plant pathogens are a serious threat to agriculture and to global food security, causing diverse crop diseases which lead to extensive annual yield losses. Production of effector proteins by pathogens, to manipulate host cellular processes, is central to their success. An understanding of fundamental effector biology is key to addressing the threat posed by these pathogens. Recent advances in 'omics' technologies have facilitated high-throughput identification of putative effector proteins, while evolving cellular, structural and biochemical approaches have assisted in characterising their function. Furthermore, structures of effectors in complex with host factors now provide opportunities for applying our knowledge of effector biology to influence disease outcomes. In this review, we highlight recent advances in the field and suggest avenues for future research.

Stomatal Development and Perspectives toward Agricultural Improvement

“…To countervail plant defense systems, pathogens have elaborate strategies to interfere with the host immune system Torres et al 2006;Hann and Rathjen 2007). For instance, gram-negative bacteria Pseudomonas syringae inject effector proteins through their type III secretion system to promote infection by blocking the plant innate immune system (Alfano and Collmer 2004;Abramovitch et al 2006;Grant et al 2006;Varden et al 2017). Intriguingly, inducible overexpression of two effector proteins of P. syringae pathovar tomato strain, DC3000 (Pst DC3000), AvrPto and AvrPtoB, produces a severe clustered stomata phenotype in Arabidopsis (Meng et al 2015).…”

Sticking to it: phytopathogen effector molecules may converge on evolutionarily conserved host targets in green plants

“…In comparison, our understanding of how the cytoplasmic effectors of eukaryotic filamentous microbes are delivered into plant cells remains unclear, however it is generally believed that certain effector families (i.e. RXLR and CRN/crinkler) enter and act within host cells [10,11,17]. These molecules are likely delivered through specialized hyphal structures that invaginate plant cells (haustoria), or perhaps are endocytosed from the apoplast [18,19].…”

“…disease promotion/immune suppression) are used as baits to identify host targets in yeast 2-hybrid or immunoprecipitation-mass spectrometry (IP-MS) screens (discussed in [17]). This is then followed by more detailed analyses to validate candidate interactors and determine how the effector acts to facilitate disease progression.…”

Nonproteinaceous effectors: the terra incognita of plant–fungal interactions

“…Historically, the first effectors to be identified were small secreted proteins conferring avirulence as a result of their recognition by plant immune receptors, which led to systematic studies to identify their plant targets and receptors (Domazakis et al ., ). Thus far, the effector biology field has focused almost exclusively on secreted proteins (Varden et al ., ), without considering the potentially similar roles played by fungal secondary metabolites (SMs; chemical effectors) and small noncoding RNAs (sRNA effectors), defined collectively as nonproteinaceous effectors (NPEs) in this review. Recent advances suggest that NPEs contribute more than previously thought to the establishment of plant colonization.…”