Transcript profiling demonstrates absence of dosage compensation in Arabidopsis following loss of a single RPL23a paralog.

Translation of nucleus-encoded messages in plants is conducted by the cytoplasmic ribosome, an enzyme that is comprised of two RNA/protein subunits. In Arabidopsis thaliana, the 81 different ribosomal proteins (r-proteins) of the cytosolic ribosome belong to gene families with multiple expressed members. Given that ribosomes generally contain only one copy of each r-protein, regulatory mechanisms must exist to ensure their stoichiometric accumulation. These mechanisms must be dynamic, allowing for adjustments to ribosome biogenesis to fulfill biological requirements for protein synthesis during development, and following stress induction of global changes in gene expression. In this study, we investigated whether r-protein paralogs are feedback regulated at the transcript level by obtaining a T-DNA knockout of one member, RPL23aB, from the two-member RPL23a family. Expression of the lone functional paralog in this line, RPL23aA, was compared to the expression of both paralogs in wildtype plants under non-stressed, low temperature-, and high light stresses. RPL23aA expression was not upregulated in RPL23aB knockouts to compensate for paralog-loss, and consequently knockouts showed reduced total abundance of RPL23a transcripts. However, no phenotype developed in RPL23aB knockouts, suggesting that this paralog is dispensable under experimental conditions examined, or that compensation by RPL23aA may occur post-transcriptionally. Patterns of RPL23aA and RPL23aB transcript accumulation in wildtype plants suggest that paralogs respond coordinately to developmental and stress stimuli.

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