Abstract
Arabidopsis thaliana DBP1 belongs to the plant-specific family of DNA-binding protein phosphatases. Although recently identified as a novel host factor mediating susceptibility to potyvirus, little is known about DBP1 targets and partners and the molecular mechanisms underlying its function. Analyzing changes in the phosphoproteome of a loss-of-function dbp1 mutant enabled the identification of 14-3-3λ isoform (GRF6), a previously reported DBP1 interactor, and MAP kinase (MAPK) MPK11 as components of a small protein network nucleated by DBP1, in which GRF6 stability is modulated by MPK11 through phosphorylation, while DBP1 in turn negatively regulates MPK11 activity. Interestingly, grf6 and mpk11 loss-of-function mutants showed altered response to infection by the potyvirus Plum pox virus (PPV), and the described molecular mechanism controlling GRF6 stability was recapitulated upon PPV infection. These results not only contribute to a better knowledge of the biology of DBP factors, but also of MAPK signalling in plants, with the identification of GRF6 as a likely MPK11 substrate and of DBP1 as a protein phosphatase regulating MPK11 activity, and unveils the implication of this protein module in the response to PPV infection in Arabidopsis.
Highlights
DNA-binding protein phosphatases (DBPs) are a unique family of protein phosphatases of the 2C class that are distinctively capable of binding DNA [1]
GRF6 was previously shown to interact with DBP1 using the yeast two-hybrid system [6], an interaction conserved in tobacco and Arabidopsis
We show that DBP1 negatively regulated MPK11 activity and that GRF6 seems to be a MPK11 substrate
Summary
DNA-binding protein phosphatases (DBPs) are a unique family of protein phosphatases of the 2C class that are distinctively capable of binding DNA [1]. DBP1 function is modulated through the interaction with 14-3-3 proteins, highly conserved ubiquitous eukaryotic proteins recognized as important mediators in the regulation of diverse biological processes, in particular in signal transduction and transcription [5]. We showed that DBP1 negatively regulated MPK11 activity, and that MPK11 mediated phosphorylation of GRF6, promoting ubiquitination and increased GRF6 protein turn-over These results unveil a phosphorylation-dependent, proteasome-mediated regulatory mechanism of GRF6, and identify a likely substrate for MPK11, a MAPK with unknown function, whose activity is shown to be, in turn, modulated by DBP1. Reverse genetic studies revealed that both GRF6 and MPK11 are involved in the response of Arabidopsis plants to infection by the potyvirus Plum pox virus, and the described regulation of GRF6 protein stability by MPK11 was shown to occur during PPV infection, appearing as a novel signalling component in the Arabidopsis-PPV interaction
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