Variation in transcript abundance among the four members of the Arabidopsis thaliana RIBOSOMAL PROTEIN S15a gene family

As a ribonucleoprotein complex, the plant ribosome consists of four ribosomal RNAs (rRNAs) and 75-92 ribosomal proteins (r-proteins), depending on the species. Arabidopsis thaliana r-protein genes exist in multi-gene families ranging in size from two to seven transcriptionally active members. The cytosolic RPS15a gene family consists of four members that, at the amino acid level, share 87-100% identity. The 5′ regulatory regions of the four genes contain many of the same putative regulatory elements but share only 46-49% nucleotide sequence identity. Semi-quantitative RT-PCR (sqRT-PCR) was used to determine RPS15a transcript abundance patterns and identify possible regulatory differences among the four genes. RPS15aC expression was not detected in any tissue under any treatment while transcript abundance for RPS15aA, -D and -F was highest in mitotically active tissues e.g. bud and flower. Seedlings showed increased transcript abundance following treatment with the cytokinin 6-benzylaminopurine (BAP) while the auxin indole acetic acid (IAA) induced an increase in RPS15aF abundance only. Abscisic acid (ABA) treatment resulted in decreased transcript abundance while gibberellic acid (GA3) had little effect on all four genes. Similar trends were established for RPS15aA, -D and -F transcript abundance as a result of temperature mechanical stress. This study reports the differences in transcript abundance of the four cytosolic RPS15a genes in Arabidopsis and we suggest that RPS15a genes should no longer be considered 'housekeeping' genes.