A clone resource of Magnaporthe oryzae effectors that share sequence and structural similarities across host-specific lineages

Now published in Molecular Plant-Microbe Interactions 33:1032-1035

We describe a clone resource of 195 effectors of the blast fungus Magnaporthe oryzae. These clones are freely available as Golden Gate compatible entry plasmids. Our aim is to provide the community with an open source effector clone library to be used in a variety of functional studies.

Plant pathogens secrete effectors that play central roles in subjugating plants for colonization. Effectors typically have signal peptides, and occasionally carry conserved folds and motifs (Lo Presti et al.,2015; Franceschettiet al., 2017). Magnaporthe oryzae(Syn. Pyricularia oryzae) is an important plant pathogenthat is able to infect around 50 species of both wild and cultivated grasses including important cereals of the Poaceae family. M. oryzaeis mostly known to cause rice blast but can also cause disease on other crops such as barley, wheat, foxtail millet, and finger millet. The global population of Magnaporthe is composed of genetically differentiated lineages which, in some cases, still exhibit a measurable degree of gene flow (Gladieux et al.,2018). Fungal isolates from each of those lineages show a preference for a specific host and also encode distinct repertoires of effector genes (Yoshida et al.,2016). 

The first genomic sequence of Magnaporthe oryzaewas released in 2005 for the lab strain 70-15 and allowed to predict a large set of secreted proteins such as enzymes involved in secondary metabolism and virulence-associated factors including putative effectors (Dean et al.,2005). Recently an increasing number of genome sequences of isolates from different lineages have become available, allowing the research community to perform comparative genomic studies (Chiapello et al.,2015; Yoshida et al.,2016). 

Many of the validated effectors of M. oryzae are known as the MAX (MagnaportheAVRs and ToxB like) effectors. These effectors, while showing little primary sequence similarity, share a conserved structural fold composed of 6 β-sheets alternating in an anti-parallel manner (de Guillenet al., 2015). The MAX family has been largely expanded in Magnaportheas those effectors account for 5-10% of the effector repertoire and for 50% of the already cloned effectors of Magnaporthe(de Guillenet al., 2015). Indeed, the identification of structural motifs enables more sensitive predictions of effectors from pathogen genomes compared to sequence similarity searches (Franceschettiet al., 2017).

The aim of this project was to computationally identify a set of M. oryzaeeffectors from the main host-specific lineages and develop an open access clone resource for functional analyses.