Arabidopsis Ribosomal Proteins RPL23aA and RPL23aB Are Differentially Targeted to the Nucleolus and Are Disparately Required for Normal Development      

Abstract

Protein synthesis is catalyzed by the ribosome, a two-subunit enzyme comprised of four ribosomal RNAs and, in Arabidopsis (Arabidopsis thaliana), 81 ribosomal proteins (r-proteins). Plant r-protein genes exist as families of multiple expressed members, yet only one r-protein from each family is incorporated into any given ribosome, suggesting that many r-protein genes may be functionally redundant or development/tissue/stress specific. Here, we characterized the localization and gene-silencing phenotypes of a large subunit r-protein family, RPL23a, containing two expressed genes (RPL23aA and RPL23aB). Live cell imaging of RPL23aA and RPL23aB in tobacco with a C-terminal fluorescent-protein tag demonstrated that both isoforms accumulated in the nucleolus; however, only RPL23aA was targeted to the nucleolus with an N-terminal fluorescent protein tag, suggesting divergence in targeting efficiency of localization signals. Independent knockdowns of endogenous RPL23aA and RPL23aB transcript levels using RNA interference determined that an RPL23aB knockdown did not alter plant growth or development. Conversely, a knockdown of RPL23aA produced a pleiotropic phenotype characterized by growth retardation, irregular leaf and root morphology, abnormal phyllotaxy and vasculature, and loss of apical dominance. Comparison to other mutants suggests that the phenotype results from reduced ribosome biogenesis, and we postulate a link between biogenesis, microRNA-target degradation, and maintenance of auxin homeostasis. An additional RNA interference construct that coordinately silenced both RPL23aA and RPL23aB demonstrated that this family is essential for viability.

Pumilio Puf domain RNA-binding proteins in Arabidopsis

“…2). In spite of the phenotypic similarity of apum23 mutant to the "loss of function" mutants of nucleolin 1 (AtNuc-L1) [46][47][48] and ribosomal protein (RP) [49][50][51][52] genes, our microarray data showed the transcriptional upregulation of a portion of the RP genes, although the expression level of the AtNuc-L1 transcript did not change. However, AtNuc-L2, which is not expressed under normal growth conditions in wild-type plants, was greatly upregulated.…”

Plant L10 Ribosomal Proteins Have Different Roles during Development and Translation under Ultraviolet-B Stress

“…In Arabidopsis, numerous mutants have been described with altered leaf size and/or shape (Van Lijsebettens et al, 1994;Ito et al, 2000;Weijers et al, 2001;Nishimura et al, 2005;Degenhardt and Bonham-Smith, 2008a;Pinon et al, 2008;Yao et al, 2008;Fujikura et al, 2009;Rosado et al, 2010). rpl10B mutant plants displayed smaller palisade cells in the subepidermal layer (76% reduction) and also showed a moderate but significant decrease in cell number in the first leaves (32% reduction; Fig.…”

“…Mutations in ribosomal proteins have been reported as showing abnormalities in growth and development (Van Lijsebettens et al, 1994;Ito et al, 2000;Weijers et al, 2001;Nishimura et al, 2005;Degenhardt and Bonham-Smith, 2008a;Imai et al, 2008, Pinon et al, 2008Yao et al, 2008;Byrne, 2009;Fujikura et al, 2009;Rosado et al 2010). As mentioned above, homozygous rpl10B plants were significantly underrepresented.…”

New Evidence for Differential Roles of L10 Ribosomal Proteins from Arabidopsis

“…In this way, ribosomal heterogeneity would allow selective translation of specific mRNAs under particular cell conditions (Barakat et al, 2001;Szick-Miranda and BaileySerres, 2001;Giavalisco et al, 2005;Carroll et al, 2008;Carroll, 2013). Arabidopsis mutants in ribosomal proteins exhibit a large range of developmental phenotypes with extreme abnormalities, including embryonic lethality, suggesting that ribosomes also have specific functions regulating the expression of developmental genes (Van Lijsebettens et al, 1994;Degenhardt and Bonham-Smith, 2008;Byrne, 2009;Horiguchi et al, 2011Horiguchi et al, , 2012Szakonyi and Byrne, 2011). Furthermore, it has been recently demonstrated that ribosomal proteins control auxinmediated developmental programs by translational regulation of auxin response factors (Rosado et al, 2012).…”