Comparative large-scale analysis of interactions between several crop species and the effector repertoires from multiple pathovars of Pseudomonas and Ralstonia.

Genome Center and Department of Plant Sciences, University of California, Davis, California 95616, USA.
Plant physiology (Impact Factor: 7.39). 08/2009; 150(4):1733-49. DOI: 10.1104/pp.109.140251
Source: PubMed

ABSTRACT Bacterial plant pathogens manipulate their hosts by injection of numerous effector proteins into host cells via type III secretion systems. Recognition of these effectors by the host plant leads to the induction of a defense reaction that often culminates in a hypersensitive response manifested as cell death. Genes encoding effector proteins can be exchanged between different strains of bacteria via horizontal transfer, and often individual strains are capable of infecting multiple hosts. Host plant species express diverse repertoires of resistance proteins that mediate direct or indirect recognition of bacterial effectors. As a result, plants and their bacterial pathogens should be considered as two extensive coevolving groups rather than as individual host species coevolving with single pathovars. To dissect the complexity of this coevolution, we cloned 171 effector-encoding genes from several pathovars of Pseudomonas and Ralstonia. We used Agrobacterium tumefaciens-mediated transient assays to test the ability of each effector to induce a necrotic phenotype on 59 plant genotypes belonging to four plant families, including numerous diverse accessions of lettuce (Lactuca sativa) and tomato (Solanum lycopersicum). Known defense-inducing effectors (avirulence factors) and their homologs commonly induced extensive necrosis in many different plant species. Nonhost species reacted to multiple effector proteins from an individual pathovar more frequently and more intensely than host species. Both homologous and sequence-unrelated effectors could elicit necrosis in a similar spectrum of plants, suggesting common effector targets or targeting of the same pathways in the plant cell.


Available from: Oswaldo Ochoa, Jun 02, 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: Effectors delivered to host cells by the Type III secretion system are essential to Ralstonia solanacearum pathogenicity, as in several other plant pathogenic bacteria. The establishment of exhaustive effector repertoires in multiple R. solanacearum strains drew a first picture of the evolutionary dynamics of the pathogen effector suites. Effector repertoires are diversified, with a core of 20-30 effectors present in most of the strains and the obtention of mutants lacking one or more effector genes revealed the functional overlap among this effector network. Recent functional studies have provided insights into the ability of single effectors to manipulate the host proteasome, elicit cell death, trigger the expression of plant genes, and/or display biochemical activities on plant protein targets.
    Current Opinion in Plant Biology 05/2014; 20C:110-117. DOI:10.1016/j.pbi.2014.05.002 · 9.39 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nonhost resistance (NHR) is a plant immune response to resist most pathogens. The molecular basis of NHR is poorly understood, but recognition of pathogen effectors by immune receptors, a response known as effector-triggered immunity, has been proposed as a component of NHR. We performed transient expression of 54 Phytophthora infestansRXLR effectors in pepper (Capsicum annuum) accessions. We used optimized heterologous expression methods and analyzed the inheritance of effector-induced cell death in an F2 population derived from a cross between two pepper accessions. Pepper showed a localized cell death response upon inoculation with P. infestans, suggesting that recognition of effectors may contribute to NHR in this system. Pepper accessions recognized as many as 36 effectors. Among the effectors, PexRD8 and Avrblb2 induced cell death in a broad range of pepper accessions. Segregation of effector-induced cell death in an F2 population derived from a cross between two pepper accessions fit 15 : 1, 9 : 7 or 3 : 1 ratios, depending on the effector. Our genetic data suggest that a single or two independent/complementary dominant genes are involved in the recognition of RXLR effectors. Multiple loci recognizing a series of effectors may underpin NHR of pepper to P. infestans and confer resistance durability.
    New Phytologist 06/2014; DOI:10.1111/nph.12861 · 6.55 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In Arabidopsis, the Pseudomonas syringae effector proteins AvrB and AvrRpm1 are both detected by the RPM1 disease resistance (R) protein. In contrast, soybean can distinguish between these effectors, with AvrB and AvrRpm1 being detected by the Rpg1b and Rpg1r R proteins, respectively. We have been using these genes to investigate the evolution of R gene specificity and have previously identified RPM1 and Rpg1b. Here, we report the cloning of Rpg1r, which like RPM1 and Rpg1b, encodes a coiled-coil-nucleotide binding-leucine rich repeat (CC-NB-LRR) protein. As previously found for Rpg1b, we determined that Rpg1r is not orthologous with RPM1, indicating that the ability to detect both AvrB and AvrRpm1 evolved independently in soybean and Arabidopsis. The tightly-linked soybean Rpg1b and Rpg1r genes share a close evolutionary relationship, with Rpg1b containing a recombination event that combined a NB domain closely related to Rpg1r with CC and LRR domains from a more distantly related CC-NB-LRR gene. Using structural modeling, we mapped polymorphisms between Rpg1b and Rpg1r onto the predicted tertiary structure of Rpg1b, which revealed highly polymorphic surfaces within both the CC and LRR domains. Assessment of chimeras between Rpg1b and Rpg1r using a transient expression system revealed that AvrB versus AvrRpm1 specificity is determined by the C-terminal portion of the LRR domain. The P. syringae effector AvrRpt2, which targets RIN4 proteins in both Arabidopsis and soybean, partially blocked recognition of both AvrB and AvrRpm1 in soybean, suggesting that both Rpg1b and Rpg1r may detect these effectors via modification of a RIN4 homolog.
    Plant physiology 07/2014; 166(1). DOI:10.1104/pp.114.244715 · 7.39 Impact Factor