Plants and Microbes
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Plants and Microbes
Everything related to the science of plant-microbe interactions
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MPMI: Variable expression of the Stagonospora nodorum effector SnToxA among isolates is correlated with levels of disease in wheat

MPMI: Variable expression of the Stagonospora nodorum effector SnToxA among isolates is correlated with levels of disease in wheat | Plants and Microbes | Scoop.it
Most research on host-pathogen interactions is focused on mechanisms of resistance, but less is known regarding mechanisms of susceptibility. The wheat-Stagonospora nodorum pathosystem involves pathogen-produced effectors, also known as host-selective toxins, that interact with corresponding dominant host genes to cause disease. Recognition of the S. nodorum effectors SnToxA and SnTox2 is mediated by the wheat genes Tsn1 and Snn2, respectively. Here, we inoculated a population of wheat recombinant inbred lines that segregates for Tsn1 and Snn2 with conidia from two S. nodorum isolates, Sn4 and Sn5, which both produce SnToxA and SnTox2 to compare the effects of compatible Tsn1-SnToxA and Snn2-SnTox2 interactions between the two isolates. Genetic analysis revealed that the two interactions contribute equally to disease caused by isolate Sn4, but the Tsn1-SnToxA interaction contributed substantially more to disease conferred by Sn5 than did the Snn2-SnTox2 interaction. Sequence analysis of the SnToxA locus from Sn4 and Sn5 indicated they were 99.5% identical with no polymorphisms in the coding region or the predicted promoters. Analysis of transcription levels showed that expression levels of SnToxA peaked at 26 hours post inoculation for both isolates, but SnToxA expression in Sn5 was more than twice that of Sn4. This work demonstrates that necrotrophic effectors of different isolates can be expressed at different levels in planta, and that higher levels of expression lead to increased levels of disease in the wheat-S. nodorum pathosystem.
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Commentary: Between the Stomach and the Purse: What we can Learn From the Great Irish Famine in the 1840s

In East Africa a humanitarian disaster is fast unfolding with the spectre of famine looming.
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PNAS: Tomato Cf resistance proteins mediate recognition of cognate homologous effectors from fungi pathogenic on dicots and monocots

PNAS: Tomato Cf resistance proteins mediate recognition of cognate homologous effectors from fungi pathogenic on dicots and monocots | Plants and Microbes | Scoop.it

Most fungal effectors characterized so far are species-specific and facilitate virulence on a particular host plant. During infection of its host tomato, Cladosporium fulvum secretes effectors that function as virulence factors in the absence of cognate Cf resistance proteins and induce effector-triggered immunity in their presence. Here we show that homologs of the C. fulvum Avr4 and Ecp2 effectors are present in other pathogenic fungi of the Dothideomycete class, including Mycosphaerella fijiensis, the causal agent of black Sigatoka disease of banana. We demonstrate that the Avr4 homolog of M. fijiensis is a functional ortholog of C. fulvum Avr4 that protects fungal cell walls against hydrolysis by plant chitinases through binding to chitin and, despite the low overall sequence homology, triggers a Cf-4-mediated hypersensitive response (HR) in tomato. Furthermore, three homologs of C. fulvum Ecp2 are found in M. fijiensis, one of which induces different levels of necrosis or HR in tomato lines that lack or contain a putative cognate Cf-Ecp2 protein, respectively. In contrast to Avr4, which acts as a defensive virulence factor, M. fijiensis Ecp2 likely promotes virulence by interacting with a putative host target causing host cell necrosis, whereas Cf-Ecp2 could possibly guard the virulence target of Ecp2 and trigger a Cf-Ecp2-mediated HR. Overall our data suggest that Avr4 and Ecp2 represent core effectors that are collectively recognized by single cognate Cf-proteins. Transfer of these Cf genes to plant species that are attacked by fungi containing these cognate core effectors provides unique ways for breeding disease-resistant crops.

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