Microarray data analyses of yeast RNA Pol I subunit RPA12 deletion strain

The ribosomal RNA (rRNA) biosynthesis is the most energy consuming process in all living cells and the majority of total transcription activity is dedicated for synthesizing rRNA. The cells may adjust the synthesis of rRNA with the availability of resources. rRNA is mainly synthesized by RNA polymerase I that is composed of 14 subunits. Deletion of RPA12, 14, 39 and 49 are viable. RPA12 is a very small protein (13.6 kDa), and the amount of protein in the cells is very high (12,000 molecules per cell), but the role of this protein is unknown in other cellular metabolic processes (Kulak et al., 2014 [1]). RPA12 consists of two zinc-binding domains and it is required for the termination of rRNA synthesis (Mullem et al., 2002 [2]). Deletions of RPA12 in Saccharomyces cerevisiae and Schizosaccharomyces pombe cause a conditional growth defect (Nogi et al., 1993 [3]). In S. pombe, C-terminal deletion behaves like wild-type (Imazawa et al., 2001 [4]). This prompted us to investigate in detail the physiological role of RPA12 in S. cerevisiae, we performed the microarray of rpa12 ∆ strain and deposited into Gene Expression Omnibus under GSE68731. The analysis of microarray data revealed that the expression of major cellular metabolism genes is high. The amino acid biosynthesis, nonpolar lipid biosynthesis and glucose metabolic genes are highly expressed. The analyses also revealed that the rpa12 ∆ cells have an uncontrolled synthesis of cell metabolites, so RPA12 could be a master regulator for whole cellular metabolism.

Involvement of rRNA biosynthesis in the regulation of CUC1 gene expression and pre-meristematic cell mound formation during shoot regeneration

At an early stage of shoot regeneration from calli of Arabidopsis, pre-meristematic cell mounds develop in association with localized strong expression of CUP-SHAPED COTYLEDON (CUC) genes. Previous characterization of root initiation-defective 3 (rid3), an Arabidopsis mutant originally isolated as being temperature-sensitive for adventitious root formation, with respect to shoot regeneration implicated RID3 in the negative regulation of CUC1 expression and the restriction of cell division in pre-meristematic cell mounds. Positional cloning has identified RID3 as a WD40 repeat protein gene whose molecular function was not investigated before. Here we performed in silico analysis of RID3 and found that RID3 is orthologous to IPI3, which mediates pre-rRNA processing in Saccharomyces cerevisiae. In the rid3 mutant, rRNA precursors accumulated to a very high level in a temperature-dependent manner. This result indicates that RID3 is required for pre-rRNA processing as is IPI3. We compared rid3 with rid2, a temperature-sensitive mutant that is mutated in a putative RNA methyltransferase gene and is impaired in pre-rRNA processing, for seedling morphology, shoot regeneration, and CUC1 expression. The rid2 and rid3 seedlings shared various developmental alterations, such as a pointed-leaf phenotype, which is often observed in ribosome-related mutants. In tissue culture for the induction of shoot regeneration, both rid2 and rid3 mutations perturbed cell-mound formation and elevated CUC1 expression. Together, our findings suggest that rRNA biosynthesis may be involved in the regulation of CUC1 gene expression and pre-meristematic cell-mound formation during shoot regeneration.