From effectors to effectomes: Are functional studies of individual effectors enough to decipher plant pathogen infectious strategies?

Abstract

Effector proteins of plant pathogens are key virulence determinants which can be secreted in the apoplast or translocated inside plant cells where they subvert host immunity and physiology to the pathogen's benefit [1]. In some specific plant accessions, effector proteins may also be detected by plant immune receptors and trigger strong specific resistance [2-4]. Achievements and limits of current effectors studies in plant pathogens A pathogen's effectome (sometimes also referred to as effectorome) is the repertoire of all its effector proteins (Fig 1A). To date, most effector proteins are studied individually, omitting the broader context in which they function as the effectome. Size and composition of effectomes vary greatly between pathogens, including at the intraspecific level, ranging from as little as 4 in Erwinia amylovora to hundreds of effector proteins per isolate in some fungi, nematodes, and oomycetes (Fig 2A) [5-14]. These differences influence pathogen's virulence, lifestyle, and host range [15-17]. Known effector functions are the result of a combination of experimental approaches, often low throughput and based on in vitro or heterologous systems (Figs 1B, 2C and 2D) [18-21]. Some effectome-scale screens have been conducted, but these are still a compilation of individual effectors studies and thus present the same limitations as smaller-scale studies [22-28]. Evidences for effector-effector interferences within effectomes Studies of individual effector proteins intrinsically overlook their coordinated functions due to functional redundancy [29-31], expression patterns dependent on infection stages or plant organ [32-34], and epistatic interactions within effectomes [35-40] (Fig 2B). Therefore, effectome functions are usually not the sum of the individual effector functions (Fig 1C), and dedicated experimental approaches would be needed to determine how effectomes function as a whole. Prerequisites are the knowledge of the effectome composition, an experimentally manageable effectome size, and a genetically amenable pathogen. Consequently, functional characterization of effectomes is most advanced in bacteria [30,35,41,42] and developing at an ever increasing pace in fungi or nematodes thanks to powerful genome-editing tools [43,44] and

Genome Expression Dynamics Reveal the Parasitism Regulatory Landscape of the Root-Knot Nematode Meloidogyne incognita and a Promoter Motif Associated with Effector Genes

“…The current approaches for their study are mostly based on the analyses of a single effector at a time through its overexpression in plants, target gene silencing via RNAi, and the identification of target host proteins [ 9 ]. However, silencing of a single effector gene can be difficult to interpret because RNAi is never done at 100% efficiency, sometimes it can have a redundant role, and by consequence, its functional role may be not enough to completely alter nematode parasitism [ 9 , 81 , 82 , 83 ]. Thus, targeting the regulators associated with Mel-DOG might represent an attractive and accurate target to develop novel nematode control strategies.…”

Genome expression dynamics reveals parasitism regulatory landscape of the root-knot nematodeMeloidogyne incognitaand a promoter motif associated with effector genes

“…The current approaches for their study are mostly based on the analyses of a single effector at a time through its overexpression in plants, target gene silencing via RNAi and the identification of target host proteins [9]. However, silencing of a single effector gene can be difficult to interpret because RNAi is never done at 100%, sometimes it can have a redundant role, and by consequence, its functional role may be not enough to completely alter the nematode parasitism [9,[81][82][83]. Thus, targeting the regulators associated with Mel-DOG might represent an attractive and accurate target to develop novel nematode control strategies.…”

Comparative genomics of three Colletotrichum scovillei strains and genetic analysis revealed genes involved in fungal growth and virulence on chili pepper

“…This suggests that the 33 effectors might play a role in the virulence of Coll-524 to chili pepper. However, when one of the effectors was transferred to Coll-365, it did not promote the virulence of the transgenic strains on chili pepper fruit, suggesting that multiple effectors may work together to affect fungal virulence [45].…”