Plants are engaged in a continuous co-evolutionary struggle for dominance with their pathogens. The outcomes of these interactions are of particular importance to human activities, as they can have ...dramatic effects on agricultural systems. The recent convergence of molecular studies of plant immunity and pathogen infection strategies is revealing an integrated picture of the plant-pathogen interaction from the perspective of both organisms. Plants have an amazing capacity to recognize pathogens through strategies involving both conserved and variable pathogen elicitors, and pathogens manipulate the defence response through secretion of virulence effector molecules. These insights suggest novel biotechnological approaches to crop protection.
The first plant disease resistance (
R
) genes were identified and cloned more than two decades ago. Since then, many more
R
genes have been identified and characterized in numerous plant ...pathosystems. Most of these encode members of the large family of intracellular NLRs (NOD-like receptors), which also includes animal immune receptors. New discoveries in this expanding field of research provide new elements for our understanding of plant NLR function. But what do we know about plant NLR function today? Genetic, structural, and functional analyses have uncovered a number of commonalities and differences in pathogen recognition strategies as well as how NLRs are regulated and activate defense signaling, but many unknowns remain. This review gives an update on the latest discoveries and breakthroughs in this field, with an emphasis on structural findings and some comparison to animal NLRs, which can provide additional insights and paradigms in plant NLR function.
Apoplastic effectors, in particular, often contain several disulfide bonds 17 and predicted secretomes of pathogenic fungi contain proteins with elevated levels of cysteines compared to all ...proteins (Fig 1A). ...the criteria of small and cysteine-rich can be used to mine predicted secretomes for apoplastic effectors and reduce the number of candidates 18,19. ...an increase in the number of identified fungal effectors might enable machine learning approaches for unbiased prediction, which could lead to the discovery of protein properties common to fungal effectors.
Plant immunity is often triggered by the specific recognition of pathogen effectors by intracellular nucleotide-binding, leucine-rich repeat receptors (NLR). Plant NLRs contain an N-terminal ...signaling domain that is mostly represented by either a Toll-interleukin1 receptor (TIR) domain or a coiled coil (CC) domain. In many cases, single NLR proteins are sufficient for both effector recognition and signaling activation. However, many paired NLRs have now been identified where both proteins are required to confer resistance to pathogens. Recent detailed studies on the Arabidopsis thaliana TIR-NLR pair RRS1 and RPS4 and on the rice CC-NLR pair RGA4 and RGA5 have revealed for the first time how such protein pairs function together. In both cases, the paired partners interact physically to form a hetero-complex receptor in which each partner plays distinct roles in effector recognition or signaling activation, highlighting a conserved mode of action of NLR pairs across both monocotyledonous and dicotyledonous plants. We also describe an "integrated decoy" model for the function of these receptor complexes. In this model, a plant protein targeted by an effector has been duplicated and fused to one member of the NLR pair, where it acts as a bait to trigger defense signaling by the second NLR upon effector binding. This mechanism may be common to many other plant NLR pairs.
...new variants of Asian soybean rust (Phakopsora pachyrhizi) detected in Brazil and the United States pose a major constraint to soybean cultivation 2. Since genetic resistance can provide effective ...and chemical-free disease control, many efforts are directed towards isolating rust-resistance genes in crop plants and understanding how to best deploy them for durable resistance 3. ...the stripe rust-resistance gene Yr36 encodes a chloroplast-localised protein with kinase and steroidogenic acute regulatory protein-related transfer (START) lipid-binding domains and is proposed to reduce the detoxification of reactive oxygen species by phosphorylation of a thylakoid-associated ascorbate peroxidase, resulting in enhanced defense responses 18. Transgenic expression of the wheat Lr34 or Lr67 genes in other cereal species, such as durum wheat, barley, rice, and maize, confers resistance to multiple adapted pathogens of these crops, suggesting that the roles of these genes in infection are conserved across a wide taxonomic range 22. ...these genes have the potential to be used as new sources of basal/background resistance in other species, although it remains to be determined whether they can function in eudicots. Basal immunity would be relatively more important in interactions where the nonhost species is distantly related to the normal host, and NLR immunity more important in interactions involving a more closely related nonhost species. ...it is not surprising that many responses associated with NHR overlap those activated during host resistance 4, 27, 28, 29.
ApoplastP Sperschneider, Jana; Dodds, Peter N.; Singh, Karam B. ...
New phytologist,
March 2018, Letnik:
217, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The plant apoplast is integral to intercellular signalling, transport and plant–pathogen interactions. Plant pathogens deliver effectors both into the apoplast and inside host cells, but no ...computational method currently exists to discriminate between these localizations.
We present ApoplastP, the first method for predicting whether an effector or plant protein localizes to the apoplast.
ApoplastP uncovers features of apoplastic localization common to both effectors and plant proteins, namely depletion in glutamic acid, acidic amino acids and charged amino acids and enrichment in small amino acids. ApoplastP predicts apoplastic localization in effectors with a sensitivity of 75% and a false positive rate of 5%, improving the accuracy of cysteine-rich classifiers by > 13%. ApoplastP does not depend on the presence of a signal peptide and correctly predicts the localization of unconventionally secreted proteins. The secretomes of fungal saprophytes as well as necrotrophic, hemibiotrophic and extracellular fungal pathogens are enriched for predicted apoplastic proteins. Rust pathogens have low proportions of predicted apoplastic proteins, but these are highly enriched for predicted effectors.
ApoplastP pioneers apoplastic localization prediction using machine learning. It will facilitate functional studies and will be valuable for predicting if an effector localizes to the apoplast or if it enters plant cells.
Eukaryotic filamentous plant pathogens secrete effector proteins that modulate the host cell to facilitate infection. Computational effector candidate identification and subsequent functional ...characterization delivers valuable insights into plant–pathogen interactions. However, effector prediction in fungi has been challenging due to a lack of unifying sequence features such as conserved N‐terminal sequence motifs. Fungal effectors are commonly predicted from secretomes based on criteria such as small size and cysteine‐rich, which suffers from poor accuracy. We present EffectorP which pioneers the application of machine learning to fungal effector prediction. EffectorP improves fungal effector prediction from secretomes based on a robust signal of sequence‐derived properties, achieving sensitivity and specificity of over 80%. Features that discriminate fungal effectors from secreted noneffectors are predominantly sequence length, molecular weight and protein net charge, as well as cysteine, serine and tryptophan content. We demonstrate that EffectorP is powerful when combined with in planta expression data for predicting high‐priority effector candidates. EffectorP is the first prediction program for fungal effectors based on machine learning. Our findings will facilitate functional fungal effector studies and improve our understanding of effectors in plant–pathogen interactions. EffectorP is available at http://effectorp.csiro.au.
Rust fungi (Pucciniales, Basidiomycota) are obligate biotrophic pathogens that cause rust diseases in plants, inflicting severe damage to agricultural crops. Pucciniales possess the most complex life ...cycles known in fungi. These include an alternation of generations, the development of up to five different sporulating stages, and, for many species, the requirement of infecting two unrelated host plants during different parts of their life cycle, termed heteroecism. These fungi have been extensively studied in the past century through microscopy and inoculation studies, providing precise descriptions of their infection processes, although the molecular mechanisms underlying their unique biology are poorly understood. In this review, we cover recent genomic and life cycle transcriptomic studies in several heteroecious rust species, which provide insights into the genetic tool kits associated with host adaptation and virulence, opening new avenues for unraveling their unique evolution.
PDF
