Mitochondrial-Nuclear Interactions, Co-Transcription, and Adaptive Evolution in Cytoplasmic Male Sterility.

Prokaryotic genomes are compact and are commonly organised into operons that generate polycistronic transcripts. Plant mitochondrial genomes preserve several prokaryote-like expression features, including frequent polycistronic transcription and extensive post-transcriptional processing. At the same time, frequent rearrangement and recombination in plant mitochondria can create novel open reading frames, some of which cause cytoplasmic male sterility by perturbing mitochondrial function during pollen development. A recurring observation across species is that many sterility-associated open reading frames are co-transcribed in tandem with neighbouring mitochondrial genes, generating characteristic chimeric or extended transcripts that become key targets of nuclear fertility restorer genes. In this review, we synthesise co-transcription patterns of sterility-associated genes in two monocots (rice and maize) and two dicots (oilseed rape and sunflower), and outline how representative restorer genes recognise, cleave, destabilise, or translationally block the corresponding co-transcripts. Building on operon concepts, we discuss how co-transcription may shape transcript abundance, processing, and coupling to retrograde signalling. Finally, we summarise evidence linking sterility gene activity to reactive oxygen species homoeostasis and propose testable hypotheses for how these mitochondrial-nuclear interactions may influence plant adaptation and evolution.