The Function of the SAS10/C1D Family Protein, Thallo, in Plants

• Main Authors: Ying-Jiun Chen, 陳瀠莙
• Other Authors: Guang-Yuh Jauh
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/90249795328485461036

博士 === 國立中興大學 === 生物科技學研究所 === 105 === The nucleolus is the site of ribosomal RNA (rRNA) gene transcription, rRNA processing, and assembly of mature rRNAs with ribosomal proteins. The rRNA regulatory network underlying the structure and function of the plant nucleolus is largely unknown. We performed an in silico screen for essential genes of unknown function in Arabidopsis thaliana and identified Thallo (THAL) encoding a SAS10/C1D family protein. THAL disruption caused enlarged nucleoli in arrested embryos, aberrant processing of precursor rRNAs at the 5’ External Transcribed Spacer, and repression of the major rDNA variant (VAR1). THAL overexpression lines showed de-repression of VAR1 and overall reversed effects on rRNA processing sites. Strikingly, THAL overexpression also induced formation of multiple nucleoli per nucleus phenotypic of mutants of heterochromatin factors. THAL physically associated with histone chaperone Nucleolin 1 (NUC1), histone-binding NUC2, and histone demethylase Jumonji 14 (JMJ14) in bimolecular fluorescence complementation assay, suggesting that it participates in chromatin regulation. Furthermore, investigation of truncated THAL proteins revealed that the SAS10 C-terminal domain is likely important for its function in chromatin configuration. THAL also interacted with putative Small Subunit processome components, including previously unreported Arabidopsis homologue of yeast M Phase Phosphoprotein 10 (MPP10). Our results uncover the dual role of THAL in transcription and processing events critical for proper rRNA biogenesis and nucleolar organization during reproduction. This is the first study to define the function of SAS10/C1D family members in plants.