Biology subjects

Ponce, M. R.

Publications and source records attributed to Ponce, M. R..

3 recordsLinked to original sources

bioRxiv2023

Cross-kingdom conservation of Arabidopsis RPS24 function in 18S rRNA maturation

All 81 ribosomal proteins (RPs) that form the Arabidopsis (Arabidopsis thaliana) 80S ribosome are encoded by several paralogous genes. For example, the nearly identical RPS24A and RPS24B proteins are encoded by RPS24A and RPS24B, respectively. Here we explored the functions of RPS24A and RPS24B in Arabidopsis. Their encoding genes exhibit combined haploinsufficiency, as at least two wild-type copies of either RPS24A or RPS24B are required for plant viability and at least three are required for normal plant development. Loss-of-function of either gene caused a pointed-leaf phenotype, a typical phenotype of null or hypomorphic recessive alleles of genes encoding ribosome biogenesis factors (RBFs) or RPs. We also found that RPS24A and RPS24B act as RBFs during early stages of 18S ribosomal RNA (rRNA) maturation, as loss of RPS24A or RPS24B function reduced the 18S/25S rRNA ratio. An RPS24B-GFP fusion protein predominantly localized to the nucleolus, as expected. The rps24b-2 mutation strengthened the phenotypes of the RBF mutants mRNA transporter4-2 and small organ4-3, which are defective in 5.8S rRNA maturation. This synergistic interaction might be an effect of increased 45S rDNA transcription, which we also observed in the rps24 mutants. Therefore, the Arabidopsis RPS24 proteins act as RBFs during 18S rRNA maturation, like their human and yeast putative orthologs. Only two plant RPs were previously shown to act not only as structural components of the ribosome but also as RBFs. We provide evidence that RPS24 proteins also regulate 45S rDNA transcription, which has not been described for their yeast or human orthologs.

plant biology↗

bioRxiv2023

Analysis of Arabidopsis venosa4-0 supports the role of VENOSA4 in dNTP homeostasis

An imbalance in the deoxyribonucleoside triphosphate (dNTP) pool caused by an increase or decrease in the levels of any of the four dNTPs leads to increased DNA mutations, overloading DNA repair mechanisms. The human protein SAMHD1 (Sterile alpha motif and histidine-aspartate domain containing protein 1) functions as a dNTPase to maintain the balance of the dNTP pool, as well as in DNA repair. In eukaryotes, the limiting step in de novo dNTP synthesis is catalyzed by RIBONUCLEOTIDE REDUCTASE (RNR), which consists of two R1 and two R2 subunits. In Arabidopsis, RNR1 is encoded by CRINKLED LEAVES 8 (CLS8) and RNR2 by three paralogous genes, including TSO2 (TSO MEANING UGLY IN CHINESE 2). In plants, the de novo biosynthesis of purines occurs within the chloroplast, and DOV1 (DIFFERENTIAL DEVELOPMENT OF VASCULAR ASSOCIATED CELLS 1) catalyzes the first step of this pathway. Here, to explore the role of VENOSA4 (VEN4), the most likely Arabidopsis ortholog of human SAMHD1, we studied the ven4-0 mutant. The mutant leaf phenotype caused by the ven4-0 point mutation was stronger than those of T-DNA insertional ven4 mutations. Structural predictions suggested that the E249L amino acid substitution in the mutated VEN4-0 protein rigidifies its 3D structure compared to wild-type VEN4. The morphological phenotypes of the ven4, cls8, and dov1 single mutants were similar, and those of the ven4 tso2 and ven4 dov1 double mutants were synergistic. The ven4-0 mutant had reduced levels of four amino acids related to dNTP biosynthesis, including glutamine and glycine, which are precursors in the de novo purine biosynthesis pathway. Finally, despite its annotation in some databases, At5g40290, a paralog of VEN4, is likely a pseudogene. These observations support the previously proposed role of VEN4 in dNTP metabolism. Our results reveal a high degree of cross-kingdom functional conservation between VEN4 and SAMHD1 in dNTP homeostasis.

plant biology↗

bioRxiv2022

The Arabidopsis ATP-Binding Cassette E protein ABCE2 is a conserved component of the translation machinery

O_LIATP-Binding Cassette E (ABCE) proteins dissociate cytoplasmic ribosomes after translation terminates, and contribute to ribosome recycling, thus linking translation termination to initiation. This function has been demonstrated to be essential in animals, fungi, and archaea, but remains unexplored in plants. C_LIO_LIIn most species, ABCE is encoded by a single-copy gene; by contrast, Arabidopsis thaliana has two ABCE paralogs, of which ABCE2 seems to conserve the ancestral function. We isolated apiculata7-1 (api7-1), a viable, hypomorphic allele of ABCE2,which has a pleiotropic morphological phenotype reminiscent of mutations affecting ribosome biogenesis factors and ribosomal proteins. We also studied api7-2, a null, recessive lethal allele of ABCE2. C_LIO_LICo-immunoprecipitation experiments showed that ABCE2 physically interacts with components of the translation machinery. An RNA-seq study of the api7-1 mutant showed increased responses to iron and sulfur starvation. We also found increased transcript levels of genes related to auxin signaling and metabolism. C_LIO_LIOur results support a conserved role for ABCE proteins in ribosome recycling in plants, as previously shown for the animal, fungal, and archaeal lineages. In plants, the ABCE2 protein seems important for general growth and vascular development, likely due to an indirect effect through auxin metabolism. C_LI

plant biology↗