A Fungal Effector With Host Nuclear Localization and DNA-Binding Properties Is Required for Maize Anthracnose Development

Abstract

Plant pathogens have the capacity to manipulate the host immune system through the secretion of effectors. We identified 27 putative effector proteins encoded in the genome of the maize anthracnose pathogen Colletotrichum graminicola that are likely to target the host's nucleus, as they simultaneously contain sequence signatures for secretion and nuclear localization. We functionally characterized one protein, identified as CgEP1. This protein is synthesized during the early stages of disease development and is necessary for anthracnose development in maize leaves, stems, and roots. Genetic, molecular, and biochemical studies confirmed that this effector targets the host's nucleus and defines a novel class of double-stranded DNA-binding protein. We show that CgEP1 arose from a gene duplication in an ancestor of a lineage of monocot-infecting Colletotrichum spp. and has undergone an intense evolution process, with evidence for episodes of positive selection. We detected CgEP1 homologs in several species of a grass-infecting lineage of Colletotrichum spp., suggesting that its function may be conserved across a large number of anthracnose pathogens. Our results demonstrate that effectors targeted to the host nucleus may be key elements for disease development and aid in the understanding of the genetic basis of anthracnose development in maize plants.

A comparative genomic analysis of putative pathogenicity genes in the host-specific sibling species Colletotrichum graminicola and Colletotrichum sublineola

“…In our study, neither SignalP nor WoLF PSORT indicated the presence of a signal peptide in this protein. A second candidate nuclear effector identified in [79], GLRG_03517, was similarly not predicted to have a signal peptide in our study. A third putative NLS effector from that study (GLRG_08510) was on our list of NCPs as a predicted SSP, but not as a nuclear protein.…”

“…Some of these NCPs may also specifically target the host nucleus: for example, one of the predicted nuclear proteins in C. graminicola was GLRG_04079, aka. CgEP1, recently characterized as an essential C. graminicola effector that is targeted to the plant nucleus, with both a secretion signal and a nuclear localization signal (NLS) [79] (Additional file 5: Table S4). In our study, neither SignalP nor WoLF PSORT indicated the presence of a signal peptide in this protein.…”

“…This illustrates why localization predictions should be experimentally confirmed. The rest of the NLS effectors identified in [79] are conserved in CgSl1, and thus they were not among the NCPs.…”

Time‐resolved dissection of the molecular crosstalk driving Fusarium head blight in wheat provides new insights into host susceptibility determinism

“…Three of them were also found in the Fg exudates (fuGraFG1chr3G262700.1, fuGraFG1chr1G376300.1, and FGSG_03017) and two showed significant abundance changes during the infection (fuGraFG1chr2G224300.1 and fuGraFG1chr3G262700.1). Fungal proteins can be located in the plant nucleus to drive the success of the disease (Robin et al, ; Vargas et al, ). Such Fg proteins could partly explain the significant enrichment in wheat of FHB‐regulated proteins involved in nucleic acid binding and in translation.…”

Identification of Plasmodiophora brassicae effectors — A challenging goal

“…Another criterion used to identify putative effectors from obligate intracellular pathogens has been the presence of nuclear localization domains, which allows effectors to directly modulate plant gene expression [58,59]. For many years, effectors capable of migrating to the plant cell nucleus have only been described in bacteria [58–60], but more recently these motifs together with nuclear localization of effectors has been described in fungi [61,62] and nematodes [63]. In bioinformatics pipelines designed to identify putative effectors, the inclusion of steps to remove proteins containing subcellular localization signals will remove these effectors, although researchers could analyze these amino acid sequences directly using the online tool TargetP 1.1 Server (http://www.cbs.dtu.dk/services/TargetP).…”