Crystal Structure and Regulation of the Citrus Pol III Repressor MAF1 by Auxin and Phosphorylation

• Published in: Structure (London) 2017-09, Vol.25 (9), p.1360-1370.e4
• Main Authors: Soprano, Adriana Santos, Giuseppe, Priscila Oliveira de, Shimo, Hugo Massayoshi, Lima, Tatiani Brenelli, Batista, Fernanda Aparecida Heleno, Righetto, Germanna Lima, Pereira, José Geraldo de Carvalho, Granato, Daniela Campos, Nascimento, Andrey Fabricio Ziem, Gozzo, Fabio Cesar, de Oliveira, Paulo Sérgio Lopes, Figueira, Ana Carolina Migliorini, Smetana, Juliana Helena Costa, Paes Leme, Adriana Franco, Murakami, Mario Tyago, Benedetti, Celso Eduardo
• Format: Article
• Language: English
• Subjects: auxin signaling; Binding Sites; Cell Nucleolus - metabolism; Citrus - enzymology; Citrus - growth & development; Citrus - microbiology; Citrus sinensis; Crystallography, X-Ray; CsMAF1; Gene Expression Regulation, Developmental; Gene Expression Regulation, Plant; human MAF1; Indoleacetic Acids - metabolism; MAF1; Models, Molecular; Morpholines - pharmacology; Phosphorylation; plant cell growth; Plant Diseases - microbiology; Plant Diseases - prevention & control; Plant Proteins - chemistry; Plant Proteins - metabolism; Protein Binding; Protein Conformation; protein kinase A; Repressor Proteins - chemistry; Repressor Proteins - metabolism; TOR Serine-Threonine Kinases - metabolism; TOR signaling
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2017.07.004

MAF1 is the main RNA polymerase (Pol) III repressor that controls cell growth in eukaryotes. The Citrus ortholog, CsMAF1, was shown to restrict cell growth in citrus canker disease but its role in plant development and disease is still unclear. We solved the crystal structure of the globular core of CsMAF1, which reveals additional structural elements compared with the previously available structure of hMAF1, and explored the dynamics of its flexible regions not present in the structure. CsMAF1 accumulated in the nucleolus upon leaf excision, and this translocation was inhibited by auxin and by mutation of the PKA phosphorylation site, S45, to aspartate. Additionally, mTOR phosphorylated recombinant CsMAF1 and the mTOR inhibitor AZD8055 blocked canker formation in normal but not CsMAF1-silenced plants. These results indicate that the role of TOR on cell growth induced by Xanthomonas citri depends on CsMAF1 and that auxin controls CsMAF1 interaction with Pol III in citrus. [Display omitted] •The globular core structure of CsMAF1 shows a conserved MAF1 fold•Auxin inhibits nucleoplasm to nucleolus translocation of CsMAF1•Citrus canker suppression by TOR inhibition requires CsMAF1•CsMAF1 functions in the auxin-TOR signaling pathway In this work, Soprano et al. describe the crystal structure of citrus CsMAF1, an RNA Pol III repressor that controls cell division and growth during citrus canker disease development. They also provide evidence that auxin and the TOR kinase affect CsMAF1 nucleolar localization and function associated with pathogen-induced canker.