Abstract
Nucleostemin is a nucleolar GTP-binding protein that is involved in stem cell proliferation, embryonic development, and ribosome biogenesis in mammals. Plant nucleostemin-like 1 (NSN1) plays a role in embryogenesis, and apical and floral meristem development. In this study, a nucleolar function of NSN1 in the regulation of ribosome biogenesis was identified. Green fluorescent protein (GFP)-fused NSN1 localized to the nucleolus, which was primarily determined by its N-terminal domain. Recombinant NSN1 and its N-terminal domain (NSN1-N) bound to RNA in vitro. Recombinant NSN1 expressed GTPase activity in vitro. NSN1 silencing in Arabidopsis thaliana and Nicotiana benthamiana led to growth retardation and premature senescence. NSN1 interacted with Pescadillo and EBNA1 binding protein 2 (EBP2), which are nucleolar proteins involved in ribosome biogenesis, and with several ribosomal proteins. NSN1, NSN1-N, and EBP2 co-fractionated primarily with the 60S ribosomal large subunit in vivo. Depletion of NSN1 delayed 25S rRNA maturation and biogenesis of the 60S ribosome subunit, and repressed global translation. NSN1-deficient plants exhibited premature leaf senescence, excessive accumulation of reactive oxygen species, and senescence-related gene expression. Taken together, these results suggest that NSN1 plays a crucial role in plant growth and senescence by modulating ribosome biogenesis.
Highlights
Ribosome biogenesis is a fundamental process for making involves a series of complex processes including synthesis protein translation machinery, which is tightly co-ordinated and processing of rRNAs, chemical modification, ordered with cell growth and proliferation
nucleostemin-like 1 (NSN1) interacted with Pescadillo and EBNA1 binding protein 2 (EBP2), which are nucleolar proteins involved in ribosome biogenesis, and with several ribosomal proteins
Confocal laser scanning microscopy of leaf protoplasts revealed that Green fluorescent protein (GFP):NSN1 was predominantly localized to the nucleolus (Fig. 2B; Supplementary Fig. S4)
Summary
Ribosome biogenesis is a fundamental process for making involves a series of complex processes including synthesis protein translation machinery, which is tightly co-ordinated and processing of rRNAs, chemical modification, ordered with cell growth and proliferation. The staggering number of ribosome assembly factors in eukaryotes has hampered full understanding of the ribosomal biogenesis process. Plants encode many evolutionarily conserved ribosome assembly factors, including small nucleolar ribonucleoproteins (SnoRNPs), nucleases, RNA helicases, RNA chaperones, ATPases, and GTPases; only a small number of these factors has been functionally analysed (Pendle et al, 2005; Im et al, 2011; Cho et al, 2013; Weis et al, 2014). Recent studies suggest that ribosome assembly factor genes play a role in plant development (Byrne, 2009; Horiguchi et al, 2012)
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