Divergent Evolution of PcF/SCR74 Effectors in Oomycetes Is Associated with Distinct Recognition Patterns in Solanaceous Plants.

Plants deploy cell surface receptors known as pattern-recognition receptors (PRRs) that recognize non-self molecules from pathogens and microbes to defend against invaders. PRRs typically recognize microbe-associated molecular patterns (MAMPs) that are usually widely conserved, some even across kingdoms. Here, we report an oomycete-specific family of small secreted cysteine-rich (SCR) proteins that displays divergent patterns of sequence variation in the Irish potato famine pathogen Phytophthora infestans A subclass that includes the conserved effector PcF from Phytophthora cactorum activates immunity in a wide range of plant species. In contrast, the more diverse SCR74 subclass is specific to P. infestans and tends to trigger immune responses only in a limited number of wild potato genotypes. The SCR74 response was recently mapped to a G-type lectin receptor kinase (G-LecRK) locus in the wild potato Solanum microdontum subsp. gigantophyllum. The G-LecRK locus displays a high diversity in Solanum host species compared to other solanaceous plants. We propose that the diversification of the SCR74 proteins in P. infestans is driven by a fast coevolutionary arms race with cell surface immune receptors in wild potato, which contrasts the presumed slower dynamics between conserved apoplastic effectors and PRRs. Understanding the molecular determinants of plant immune responses to these divergent molecular patterns in oomycetes is expected to contribute to deploying multiple layers of disease resistance in crop plants.IMPORTANCE Immune receptors at the plant cell surface can recognize invading microbes. The perceived microbial molecules are typically widely conserved and therefore the matching surface receptors can detect a broad spectrum of pathogens. Here we describe a family of Phytophthora small extracellular proteins that consists of conserved subfamilies that are widely recognized by solanaceous plants. Remarkably, one subclass of SCR74 proteins is highly diverse, restricted to the late blight pathogen Phytophthora infestans and is specifically detected in wild potato plants. The diversification of this subfamily exhibits signatures of a coevolutionary arms race with surface receptors in potato. Insights into the molecular interaction between these potato-specific receptors and the recognized Phytophthora proteins are expected to contribute to disease resistance breeding in potato.

The ELR-SOBIR1 Complex Functions as a Two-Component Receptor-Like Kinase to Mount Defense Against Phytophthora infestans.

The ELICITIN RESPONSE protein (ELR) from Solanum microdontum can recognize INF1 elicitin of Phytophthora infestans and trigger defense responses. ELR is a receptor-like protein (RLP) that lacks a cytoplasmic signaling domain and is anticipated to require interaction with a signaling-competent receptor-like kinase. SUPPRESSOR OF BIR1-1 (SOBIR1) has been proposed as a general interactor for RLPs involved in immunity and, as such, is a potential interactor for ELR. Here, we investigate whether SOBIR1 is required for response to INF1 and resistance to P. infestans and whether it associates with ELR. Our results show that virus-induced gene silencing of SOBIR1 in Nicotiana benthamiana leads to loss of INF1-triggered cell death and increased susceptibility to P. infestans. Using genetic complementation, we found that the kinase activity of SOBIR1 is required for INF1-triggered cell death. Coimmunoprecipitation experiments showed that ELR constitutively associates with potato SOBIR1 in planta, forming a bipartite receptor complex. Upon INF1 elicitation, this ELR-SOBIR1 complex recruits SERK3 (SOMATIC EMBRYOGENESIS RECEPTOR KINASE 3) leading to downstream signaling activation. Overall, our study shows that SOBIR1 is required for basal resistance to P. infestans and for INF1-triggered cell death and functions as an adaptor kinase for ELR.

Verticillium dahliae LysM effectors differentially contribute to virulence on plant hosts.

Chitin-binding lysin motif (LysM) effectors contribute to the virulence of various plant-pathogenic fungi that are causal agents of foliar diseases. Here, we report the LysM effectors of the soil-borne fungal vascular wilt pathogen Verticillium dahliae. Comparative genomics revealed three core LysM effectors that are conserved in a collection of V. dahliae strains. Remarkably, and in contrast with the previously studied LysM effectors of other plant pathogens, no expression of core LysM effectors was monitored in planta in a taxonomically diverse panel of host plants. Moreover, targeted deletion of the individual LysM effector genes in V. dahliae strain JR2 did not compromise virulence in infections on Arabidopsis, tomato or Nicotiana benthamiana. Interestingly, an additional lineage-specific LysM effector is encoded in the genome of V. dahliae strain VdLs17, but not in any other V. dahliae strain sequenced to date. Remarkably, this lineage-specific effector is expressed in planta and contributes to the virulence of V. dahliae strain VdLs17 on tomato, but not on Arabidopsis or N. benthamiana. Functional analysis revealed that this LysM effector binds chitin, is able to suppress chitin-induced immune responses and protects fungal hyphae against hydrolysis by plant hydrolytic enzymes. Thus, in contrast with the core LysM effectors of V. dahliae, this lineage-specific LysM effector of strain VdLs17 contributes to virulence in planta.

Nine things to know about elicitins.

888 I. 888 II. 889 III. 889 IV. 889 V. 891 VI. 891 VII. 891 VIII. 892 IX. 892 X. 893 XI. 893 893 References 893 SUMMARY: Elicitins are structurally conserved extracellular proteins in Phytophthora and Pythium oomycete pathogen species. They were first described in the late 1980s as abundant proteins in Phytophthora culture filtrates that have the capacity to elicit hypersensitive (HR) cell death and disease resistance in tobacco. Later, they became well-established as having features of microbe-associated molecular patterns (MAMPs) and to elicit defences in a variety of plant species. Research on elicitins culminated in the recent cloning of the elicitin response (ELR) cell surface receptor-like protein, from the wild potato Solanum microdontum, which mediates response to a broad range of elicitins. In this review, we provide an overview on elicitins and the plant responses they elicit. We summarize the state of the art by describing what we consider to be the nine most important features of elicitin biology.

Successful Agrobacterium mediated transformation of Thielaviopsis basicola by optimizing multiple conditions.

Thielaviopsis basicola is a hemibiotrophic root pathogen causing black root rot in a wide range of economically important crops. Our initial attempts to transform T. basicola using standard Agrobacterium tumefaciens-mediated transformation (ATMT) protocols were unsuccessful. Successful transformation required the addition of V8 juice (to induce germination of T. basicola chlamydospores) and higher concentrations of acetosyringone in the co-cultivation medium, and of chlamydospores/endoconidia, A. tumefaciens cells during co-cultivation. With these modifications, two T. basicola strains were successfully transformed with the green (egfp) or red (AsRed) fluorescent protein genes. Chlamydospores/endoconidia transformed with the egfp gene exhibited strong green fluorescence, but their fluorescence became weaker as the germ tubes emerged. Transformants harbouring the AsRed gene displayed strong red fluorescence in both chlamydospores/endoconidia and germ tubes. Fluorescent microscopic observations of an AsRed-labelled strain colonizing roots of transgenic Nicotiana benthamiana plants, which express the actin filaments labelled with EGFP, at 24 hours post inoculation showed varying levels of fungal germination and penetration. At this stage, the infection appeared to be biotrophic with the EGFP-labelled host actin filaments not being visibly degraded, even in host root cells in close contact with the hyphae. This is the first report of ATMT of T. basicola, and the use of an AsRed-labelled strain to directly observe the root infection process.