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Review
, 39 (8), 581-6

Post-Translational Regulation of miRNA Pathway Components, AGO1 and HYL1, in Plants

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Review

Post-Translational Regulation of miRNA Pathway Components, AGO1 and HYL1, in Plants

Seok Keun Cho et al. Mol Cells.

Abstract

Post-translational modifications (PTMs) of proteins are essential to increase the functional diversity of the proteome. By adding chemical groups to proteins, or degrading entire proteins by phosphorylation, glycosylation, ubiquitination, neddylation, acetylation, lipidation, and proteolysis, the complexity of the proteome increases, and this then influences most biological processes. Although small RNAs are crucial regulatory elements for gene expression in most eukaryotes, PTMs of small RNA microprocessor and RNA silencing components have not been extensively investigated in plants. To date, several studies have shown that the proteolytic regulation of AGOs is important for host-pathogen interactions. DRB4 is regulated by the ubiquitin-proteasome system, and the degradation of HYL1 is modulated by a de-etiolation repressor, COP1, and an unknown cytoplasmic protease. Here, we discuss current findings on the PTMs of microprocessor and RNA silencing components in plants.

Keywords: AGO1; HYL1; UPS; autophagy; miRNA; protease; proteolysis.

Figures

Fig. 1.
Fig. 1.
A model for the proteolytic regulation of AGO1. (A) Viral P0 or endogenous F-box protein FBW2 mediate AGO1 destabilization. P0 protein hi-jacks the host SCF-complex to modify AGO1 and is then subjected to autophagic degradation following de-ubiquitination. FBW2 may perform a similar process through the SCF complex. (B) Viral P25 suppressor mediated AGO1 destabilization. In contrast to the role of P0, P25 seems to guide the ubiquitinated AGO1 into the 26S proteasome. (C) AGO1 is specifically cleaved into a ∼45-kDa polypeptide with or without viral suppressors. Thus, an unknown cleavage pathway may exist to turn over AGO1 activity.
Fig. 2.
Fig. 2.
A model of the proteolytic regulation of HYL1 for miRNA homeostasis. During the day, COP1 moves to the cytoplasm and suppresses the cleavage of HYL1 by protease X. COP1 remobilizes into the nucleus liberating the protease X at night. Non-canonical role of COP1, which is unrelated to the UPS pathway, may be responsible for the suppression of protease X.

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