bims-plasge 2025-09-14 papers

Issue of 2025–09–14
three papers selected by
Vera S. Bogdanova, ИЦиГ СО РАН

Physiol Plant. 2025 Sep-Oct;177(5):177(5): e70507

PPR596 Is Required for nad2 mRNA Splicing and Complex I Biogenesis in Mitochondria of Arabidopsis thaliana.

Leonora Peters, Vera C Wagner, Theresa Schoeller, Sarlita Dwiani, Mareike Schallenberg-Rüdinger, Etienne H Meyer, Kristina Kühn.

Several genes in the mitochondria of angiosperms are interrupted by introns, and their posttranscriptional excision involves numerous nucleus-encoded auxiliary factors. Most of these factors are of eukaryotic origin, among them members of the pentatricopeptide-repeat (PPR) family of RNA-binding proteins. This family divides into the PLS and P classes, with PLS-class proteins typically participating in C-to-U mRNA editing and P-class members contributing to transcript stabilization and intron splicing. The P-class protein PPR596 was previously described to be involved in mitochondrial RNA editing, with the ppr596 mutant showing moderately elevated editing of a specific, partially edited site within the rps3 mRNA. PPR596 disruption led to a substantial delay in plant development. Because the moderate change in RNA editing in the ppr596 mutant is unlikely to be the cause of its severe developmental retardation, we re-investigated mitochondrial gene expression and found that PPR596 is specifically required for the efficient excision of the third intron from the nad2 pre-mRNA. Insufficient splicing of this intron in ppr596 impairs respiratory-chain complex I biogenesis at the step of the insertion of the Nad2 subunit, thus perturbing plant development.

Keywords: PPR protein; plant mitochondria; splicing

DOI: https://doi.org/10.1111/ppl.70507

Int J Mol Sci. 2025 Aug 28. pii: 8337. [Epub ahead of print]26(17):

Characterization and Transcriptome Analysis Reveal Abnormal Pollen Germination in Cytoplasmic Male Sterile Tomato.

Kosuke Kuwabara, Tohru Ariizumi.

Cytoplasmic male sterility (CMS) is a plant trait wherein plants cannot develop normal male organs because of the mitochondrial genes. Although the mitochondrial gene orf137 has been identified as the CMS-causing gene in tomatoes, its function remains unclear. In this study, we characterized the sterile male phenotypes and analyzed the CMS pollen transcriptome. Microscopic and calcium imaging analyses revealed that CMS pollen exhibited abnormal germination from multiple apertures, accompanied by elevated calcium concentrations and vesicle accumulation, which are typically observed in pollen tube tips. RNA-Seq analysis revealed 440 differentially expressed genes, including four pectin methylesterase inhibitor (PMEI) genes that were highly expressed in the pollen. PME activity was significantly reduced in CMS pollen, suggesting its association with abnormal pollen germination. ATP and reactive oxygen species (ROS) levels, which are key mediators of mitochondrial retrograde signaling (MRS), remained unchanged in CMS pollen, and the expression of the mitochondrial stress marker AOX1a was not elevated. These findings suggest that orf137 triggers an alternative MRS pathway independent of ATP or ROS, potentially leading to PMEI upregulation and abnormal pollen germination. Our results reveal a previously unrecognized mechanism of CMS-induced male sterility in tomatoes involving nuclear gene regulation through unconventional mitochondrial signaling.

Keywords: cytoplasmic male sterility; pectin methylesterase inhibitor; pollen germination; tomato; transcriptome

DOI: https://doi.org/10.3390/ijms26178337

Int J Mol Sci. 2025 Aug 27. pii: 8310. [Epub ahead of print]26(17):

Tetratricopeptide Repeat 2 Is a Quantitative Trait Locus That Controls Seed Size.

Zhuolun Wang, Stephanie Cara, Seung Y Rhee, Bernard A Hauser.

Seed size is a key trait affecting evolution and agronomic performance by influencing seedling establishment in natural populations and crop yields. The Arabidopsis thaliana Seed Size QTL1 (SSQ1) locus explains 10-15% of the variation in seed size. We report here that the causal gene for this locus is Tetratricopeptide Repeat Protein 2 (TPR2), which encodes a co-chaperone. Expressing TPR2 across ecotypes and genotypes showed consistent dosage effects. Each additional TPR2Col-0 allele increased seed mass and volume by 10-14% with high reliability in Col-0, Sha, Tsu-1, and tsu2 genetic backgrounds. Reciprocal genetic crosses indicated that this locus acts maternally, consistent with female sporophytic or female gametophytic mutations. To elucidate how TPR2 regulates seed size, the biomass composition of seeds was measured. While oil content remained unchanged, sucrose levels were markedly elevated in TPR2Col-0 transformant lines and reduced in tpr2 mutants. Interestingly, heterologous expression of TPR2Col-0 across genetic backgrounds increased seed protein accumulation by 18% on average. Based on these changes in sucrose and protein levels, potential modes of action for TPR2 are discussed.

Keywords: Arabidopsis thaliana; QTL; assimilate transfer; seed development; seed size

DOI: https://doi.org/10.3390/ijms26178310