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Structural and functional analysis of the RNA polymerase iii repressor Maf1 involved in cell growth control and pathogen response in plants

Grant number: 18/08535-4
Support type:Regular Research Grants
Duration: September 01, 2018 - August 31, 2020
Field of knowledge:Biological Sciences - Biochemistry
Principal Investigator:Celso Eduardo Benedetti
Grantee:Celso Eduardo Benedetti
Home Institution: Centro Nacional de Pesquisa em Energia e Materiais (CNPEM). Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brasil). Campinas , SP, Brazil


Xanthomonas citri, the causal agent of citrus canker, employs the type III secretion system to inject transcription activator-like (TAL) effectors into the host cell. Such proteins, known as PthAs, act as transcription factors activating target genes that promote pathogen growth and contribute to disease development. However, besides activating target genes in the host, we found that PthA4, required to elicit cankers on citrus, interact with citrus CsMaf1, an RNA polymerase (Pol) III repressor that negatively regulates cell growth. Because CsMaf1 inhibits cell growth during canker development, it was suggested that PthA4 would inhibit its activity to promote Pol III transcription and cell growth. Therefore, one of the aims of this research is to establish how PthA4 binds CsMaf1 by mapping the protein domains involved in the interaction. We also found previously that CsMaf1 has a putative sumoylation site and is phosphorylated by PKA and TOR kinases, which control cell proliferation and defense responses in plants. Our data suggest that phosphorylation by TOR would regulate CsMaf1 binding to Pol III, whereas phosphorylation by PKA would regulate CsMaf1 localization to the nucleolus. Therefore, we plan to identify the citrus Pol III subunits that interact with CsMaf1 to subsequently analyze whether post-transcriptional modifications like phosphorylation and sumoylation regulate the CsMaf1 interaction with Pol III subunits or even PthA4. Attempts will be made to obtain protein crystals of CsMaf1-PthA4 and/or CsMaf1-Pol III subunit complexes for structural resolution. We believe that this work will help to understand how Maf1 proteins repress Pol III transcription and how TAL effectors disrupt the CsMaf1-Pol III interaction to enhance cell growth and proliferation in citrus. (AU)