bims-mitran 2023-01-29 papers

Issue of 2023–01–29
three papers selected by
Andreas Kohler, University of Graz

Proc Natl Acad Sci U S A. 2023 Jan 31. 120(5): e2216851120

Cytosolic and mitochondrial ribosomal proteins mediate the locust phase transition via divergence of translational profiles.

Jing Li, Liya Wei, Yongsheng Wang, Haikang Zhang, Pengcheng Yang, Zhangwu Zhao, Le Kang.

The phase transition from solitary to gregarious locusts is crucial in outbreaks of locust plague, which threaten agricultural yield and food security. Research on the regulatory mechanisms of phase transition in locusts has focused primarily on the transcriptional or posttranslational level. However, the translational regulation of phase transition is unexplored. Here, we show a phase-dependent pattern at the translation level, which exhibits different polysome profiles between gregarious and solitary locusts. The gregarious locusts exhibit significant increases in 60S and polyribosomes, while solitary locusts possess higher peaks of the monoribosome and a specific "halfmer." The polysome profiles, a molecular phenotype, respond to changes in population density. In gregarious locusts, ten genes involved in the cytosolic ribosome pathway exhibited increased translational efficiency (TE). In solitary locusts, five genes from the mitochondrial ribosome pathway displayed increased TE. The high expression of large ribosomal protein 7 at the translational level promotes accumulation of the free 60S ribosomal subunit in gregarious locusts, while solitary locusts employ mitochondrial small ribosomal protein 18c to induce the assembly of mitochondrial ribosomes, causing divergence of the translational profiles and behavioral transition. This study reveals the translational regulatory mechanism of locust phase transition, in which the locusts employ divergent ribosome pathways to cope with changes in population density.

Keywords: behavioral aggregation; cytosolic and mitochondrial ribosomal proteins; migratory locust; phase transition; translational regulation

DOI: https://doi.org/10.1073/pnas.2216851120

Plant Physiol. 2023 Jan 27. pii: kiad024. [Epub ahead of print]

Mitochondrial gene defects in Arabidopsis can broadly affect mitochondrial gene expression through copy number.

Hiroki Ayabe, Atsushi Toyoda, Akitoshi Iwamoto, Nobuhiro Tsutsumi, Shin-Ichi Arimura.

How mitochondria regulate the expression of their genes is poorly understood, partly because methods have not been developed for stably transforming mitochondrial genomes. In recent years, the disruption of mitochondrial genes has been achieved in several plant species using mitochondria-localized TALEN (mitoTALEN). In this study, we attempted to disrupt the NADH dehydrogenase subunit7 (NAD7) gene, a subunit of respiratory chain complex I, in Arabidopsis (Arabidopsis thaliana) using the mitoTALEN method. In some of the transformants, disruption of NAD7 was accompanied by severe growth inhibition and lethality, suggesting that NAD7 has an essential function in Arabidopsis. In addition, the mitochondrial genome copy number and overall expression of genes encoding mitochondrial proteins were generally increased by nad7 knockout. Similar increases were also observed in mutants with decreased NAD7 transcripts and with dysfunctions of other mitochondrial respiratory complexes. In these mutants, expression of nuclear genes involved in mitochondrial translation or protein transport was induced in sync with mitochondrial genes. Mitochondrial genome copy number was also partly regulated by the nuclear stress-responsive factors NAC domain containing protein 17 (ANAC017) and Radical cell death 1 (RCD1). These findings suggest the existence of overall gene-expression control through mitochondrial genome copy number in Arabidopsis and that disruption of single mitochondrial genes can have additional broad consequences in both the nuclear and mitochondrial genomes. (206/250 words).

DOI: https://doi.org/10.1093/plphys/kiad024

Commun Biol. 2023 Jan 23. 6(1): 93

The metazoan landscape of mitochondrial DNA gene order and content is shaped by selection and affects mitochondrial transcription.

Noam Shtolz, Dan Mishmar.

Mitochondrial DNA (mtDNA) harbors essential genes in most metazoans, yet the regulatory impact of the multiple evolutionary mtDNA rearrangements has been overlooked. Here, by analyzing mtDNAs from ~8000 metazoans we found high gene content conservation (especially of protein and rRNA genes), and codon preferences for mtDNA-encoded tRNAs across most metazoans. In contrast, mtDNA gene order (MGO) was selectively constrained within but not between phyla, yet certain gene stretches (ATP8-ATP6, ND4-ND4L) were highly conserved across metazoans. Since certain metazoans with different MGOs diverge in mtDNA transcription, we hypothesized that evolutionary mtDNA rearrangements affected mtDNA transcriptional patterns. As a first step to test this hypothesis, we analyzed available RNA-seq data from 53 metazoans. Since polycistron mtDNA transcripts constitute a small fraction of the steady-state RNA, we enriched for polycistronic boundaries by calculating RNA-seq read densities across junctions between gene couples encoded either by the same strand (SSJ) or by different strands (DSJ). We found that organisms whose mtDNA is organized in alternating reverse-strand/forward-strand gene blocks (mostly arthropods), displayed significantly reduced DSJ read counts, in contrast to organisms whose mtDNA genes are preferentially encoded by one strand (all chordates). Our findings suggest that mtDNA rearrangements are selectively constrained and likely impact mtDNA regulation.

DOI: https://doi.org/10.1038/s42003-023-04471-4