Translation initiation factor eIF4G1 modulates assembly of the polypeptide exit tunnel region in yeast ribosome biogenesis

Brix protein APPAN plays a role in ribosomal RNA processing in Arabidopsis

Arabidopsis APPAN is a Brix family protein that is homologous to yeast Ssf1/Ssf2 and PPan in higher eukaryotes. A previous study, mostly based on physiological experiments, revealed that APPAN plays an essential role in female gametogenesis in plants. Here, we investigated cellular functions of APPAN, which could be the molecular basis for developmental defects in snail1/appan mutants. Virus-induced gene silencing (VIGS) of APPAN in Arabidopsis resulted in abnormal shoot apices, leading to defective inflorescences and malformed flowers and leaves. APPAN is localized in the nucleolus and co-sedimented mainly with 60S ribosome subunit. RNA gel blot analyses showed overaccumulation of processing intermediates, particularly 35S and P-A₃, and the sequences were confirmed by circular RT-PCR. These results suggested that silencing of APPAN causes defective pre-rRNA processing. Metabolic rRNA labeling showed that APPAN depletion mainly reduced 25S rRNA synthesis. Consistently, based on the ribosome profiling, the levels of 60S/80S ribosomes were significantly reduced. Finally, APPAN deficiency caused nucleolar stress with abnormal nucleolar morphology and translocation of nucleolar proteins into the nucleoplasm. Collectively, these results suggest that APPAN plays a crucial role in plant rRNA processing and ribosome biogenesis, and its depletion disrupts plant growth and development.

First person – Yun-Ting Tseng

First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Yun-Ting Tseng is first author on ‘ Translation initiation factor eIF4G1 modulates assembly of the polypeptide exit tunnel region in yeast ribosome biogenesis’, published in JCS. Yun-Ting is a PhD student in the lab of Kai-Yin Lo at the Department of Agricultural Chemistry, College of Bioresources and Agriculture, National Taiwan University, working within the field of ribosome biogenesis, exploring how ribosomes are assembled and matured correctly.