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Investigating the Activation of the Tm2‐2 Immune Receptor in Response to the Tobamovirus Movement Protein
Author(s) -
Sandoval Carina,
Sacco Melanie A.
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.600.9
Subject(s) - effector , biology , microbiology and biotechnology , immune system , immune receptor , nicotiana benthamiana , movement protein , genetics , virus , gene , rna , coat protein
Effector‐triggered immunity (ETI) is a plant defense mechanism that evolved to detect pathogen effector proteins and initiate immune responses. Effectors are recognized by a direct or indirect interaction with plant immune receptor proteins. ETI often limits pathogen proliferation by promoting hypersensitive response (HR), a type of programmed cell death. In tomato ( Solanum lycopersicum ), the Tm2‐2 immune receptor provides resistance to Tobamovirus 30kDa movement protein. Tm2‐2 belongs to the CC‐NBS‐LRR class of resistance proteins, for which activation is mediated by specific intramolecular domain interactions. To study Tm2‐2 activation, mutations were introduced into the full‐length and truncated CC (coiled‐coil) domain clones. Highly conserved threonine or serine residues at positions 7, 8 and 13 were identified as potential phosphorylation targets and were mutated to aspartic acid (T7D, S8D, S13D) or to alanine (T7A, S8A, S13A). Nicotiana benthamiana was used for transient expression of constructs to observe for the effects of mutations on HR. Expression of the truncated CC domain clones with T7A or T7D mutations did not induce the HR in the presence or absence of the viral effector protein. The CC domain of the immune receptor with the effector protein is not sufficient to activate the plant's immune response. The full‐length T7D clone failed to elicit HR in the presence of the effector protein, showing loss of function. Unexpectedly, the full‐length T7A clone retained function and triggered HR in the presence of the effector protein. This evidence supports our hypothesis that position 7 of Tm2‐2 is a phosphorylation target that negatively regulates the activation of the Tm2‐2 immune receptor such that Tm2‐2 is inhibited in the charged state, but when neutral, Tm2‐2 is competent for activation of plant defenses. Understanding the mechanism of activation for Tm2‐2 can inform future engineering of efficient immune receptors that confer resistance against various pathogens. Support or Funding Information This project is supported by the Howard Hughes Medical Institute undergraduate research grant.