Elucidating the Role of Effectors in Plant-Fungal Interactions: Progress and Challenges

Abstract

Pathogenic fungi have diverse growth lifestyles that support fungal colonization on plants. Successful colonization and infection for all lifestyles depends upon the ability to modify living host plants to sequester the necessary nutrients required for growth and reproduction. Secretion of virulence determinants referred to as “effectors” is assumed to be the key governing factor that determines host infection and colonization. Effector proteins are capable of suppressing plant defense responses and alter plant physiology to accommodate fungal invaders. This review focuses on effector molecules of biotrophic and hemibiotrophic plant pathogenic fungi, and the mechanism required for the release and uptake of effector molecules by the fungi and plant cells, respectively. We also place emphasis on the discovery of effectors, difficulties associated with predicting the effector repertoire, and fungal genomic features that have helped promote effector diversity leading to fungal evolution. We discuss the role of specific effectors found in biotrophic and hemibiotrophic fungi and examine how CRISPR/Cas9 technology may provide a new avenue for accelerating our ability in the discovery of fungal effector function.

Cross-talk of the biotrophic pathogen Claviceps purpurea and its host Secale cereale

“…Especially their role in biotrophic and hemibiotrophic fungi has been under intensive investigation as these lifestyles require intact, living plant cells. Generally, effectors can modulate the host’s metabolism and directly influence defense reactions thus helping with establishing compatible interactions [5–7]. In addition to these proteinaceous effectors, secreted fungal low-molecular weight compounds like reactive oxygen species [8] or secondary metabolites, like plant hormones [9] have turned out to be important for compatible interactions.…”

Chitinases as Antibacterial Proteins: A Systematic Review

“…ChiS is a GH18 enzyme, like hevamine, but the amino acid sequences of FI and FII were not reported, and the GH families to which they belong are not known. GH18 members adopt a conserved (β/α) 8 -barrel fold that do not share similarity with the lyzosyme-type fold. Furthermore, the cleavage specificities of hevamine and lysozymes for PG are distinct: hevamine hydrolyzes the linkage between the C-1 of GlcNAc and the C-4 of MurNAc, 35 whereas lysozymes cleave the PG chains between the C-1 of MurNAc and the C-4 of GlcNAc.…”

“…The hydrolytic action of these induced chitinases on the chitin fibers of the pathogen's cell wall impairs its growth and spread, whereas the chitin oligomers released are recognized by plant chitin receptors, which trigger other defense reactions. 8 In carnivorous plants, some chitinases also play a digestive role, being used along with other hydrolytic enzymes to digest caught prey in their pitchers. 9 The great interest in the study of chitinases primarily relies on their enzymatic action on chitin.…”

Durum wheat and septoria tritici blotch: genes and prospects for breeding

“…Effectors are commonly defined as small secreted molecules from a microbe that can alter host cell structure and function, facilitating infection, such as host-selective toxins in necrotrophic fungi (Friesen et al 2008), and/or trigger defence responses, known as (a)virulence factors, such as in biotrophic fungi (Selin et al 2016;Tan and Oliver 2017). Several bacterial, fungal and oomycetes effector genes have been studied and functionally characterized.…”