Editors' ChoiceHost-Pathogen Interactions

Blocking a signal to host cell histones

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Sci. Signal.  25 Apr 2017:
Vol. 10, Issue 476, eaan4979
DOI: 10.1126/scisignal.aan4979

A plant pathogen suppresses the host immune response by preventing histone acetylation.

Plants regulate genes involved in immune responses against pathogens through several mechanisms, including histone acetylation. The histone acetyltransferase (HAT) GCN5 acetylates the tail of histone H3, activating expression of immunity-related genes. Kong et al. found that the oomycete pathogen Phytophthora sojae evaded the defenses of its soybean host by interfering with this acetylation reaction. The authors examined the P. sojae virulence effector PsAvh23, which was required for induction of disease symptoms in soybean leaves. When soybean roots expressing PsAvh23 were infected with P. sojae, the pathogen produced twice as many spores as it did in control plants. Fluorescently labeled PsAvh23 expressed in the plant localized to the nucleus of the plant cells, and PsAvh23 in infected plants associated with a soybean homolog of ADA2, a component of the plant nucleosome-acetylating complex SAGA, of which GCN5 is the catalytic subunit. PsAvh23 expressed in plants failed to promote the proliferation of pathogen spores when its ADA2-interacting region was mutated, indicating that the interaction between the effector and ADA2 drove the increase in virulence. By competitively binding to ADA2, PsAvh23 inhibited the association between ADA2 and GCN5. In ADA2 and GCN5 knockdown plants, spore production and biomass of P. sojae increased regardless of whether the plants were infected with the wild-type pathogen or a PsAvh23-knockout strain. When expressed in plant roots, PsAvh23, but not its non-interacting mutated forms, reduced the specific acetylation of histone H3 when the plant was infected, which in turn correlated with the reduced expression of immunity-related genes. Together, these results suggest that a pathogen can improve its survival and proliferation in a host by interfering with the formation of a complex required for histone acetylation and thus the expression of defense-related genes.

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