Abstract
Oomycete pathogens produce a large number of CRN effectors to manipulate plant immune responses and promote infection. However, their functional mechanisms are largely unknown. Here, we identified a Phytophthora sojae CRN effector PsCRN108 which contains a putative DNA-binding helix-hairpin-helix (HhH) motif and acts in the plant cell nucleus. Silencing of the PsCRN108 gene reduced P. sojae virulence to soybean, while expression of the gene in Nicotiana benthamiana and Arabidopsis thaliana enhanced plant susceptibility to P. capsici. Moreover, PsCRN108 could inhibit expression of HSP genes in A. thaliana, N. benthamiana and soybean. Both the HhH motif and nuclear localization signal of this effector were required for its contribution to virulence and its suppression of HSP gene expression. Furthermore, we found that PsCRN108 targeted HSP promoters in an HSE- and HhH motif-dependent manner. PsCRN108 could inhibit the association of the HSE with the plant heat shock transcription factor AtHsfA1a, which initializes HSP gene expression in response to stress. Therefore, our data support a role for PsCRN108 as a nucleomodulin in down-regulating the expression of plant defense-related genes by directly targeting specific plant promoters.
Highlights
Filamentous pathogens produce a large number of host intracellular effectors to suppress host immune responses and facilitate colonization [1,2,3]
We found that PsCRN108 targeted Heat Shock Protein (HSP) promoters in an Heat Shock Element (HSE)- and HhH motif-dependent manner
Using a GUS expression assay, we found that the effector suppressed the induction of genes driven by the AtHSP90.1 promoter or a synthetic Heat Shock Element (HSE)
Summary
Filamentous pathogens produce a large number of host intracellular effectors to suppress host immune responses and facilitate colonization [1,2,3]. Two groups of intracellular effectors (RxLR, Arg, any amino acid, Leu, Arg; CRN, Crinkler or crinkling- and necrosis-inducing protein) have been identified [3,4,5,6]. Their biochemical activities and molecular mechanisms are incompletely understood. We recently found that two effectors (PsIsc and PsAvr3b) in P. sojae act as enzymes to suppress accumulation of the essential defense compounds salicylic acid and H2O2 [9,10]
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