Beyond Arabidopsis: recent insights into the mTERF gene family across plant species.

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conclusionPlant mTERF genes have undergone extensive evolutionary expansion and perform multifunctional regulation of organelle gene expression, playing crucial roles in development and responses to environmental stress. Chloroplasts and mitochondria in higher plants maintain their own genomes, the plastome and mitogenome, which have co-evolved with the nucleus since their endosymbiotic origin. Given the limited coding capacity of these organelles, their gene expression depends heavily on nuclear-encoded proteins. Amongst the most important regulators of this nuclear-organelle coordination are the modular helical repeat protein families, specifically the pentatricopeptide repeat (PPR) and mitochondrial transcription termination factor (mTERF) families. Initially characterised in animals as four mitochondrial subfamilies, mTERFs have undergone massive expansion and functional diversification within the plant kingdom. Studies, primarily in the model organism Arabidopsis thaliana, have demonstrated that mTERF proteins are essential for organelle biogenesis and plant development. Mutations in these genes often lead to severe phenotypes, including pigment loss, growth retardation, and lethality. In addition to their roles in development, mTERFs have been identified as key players in abiotic stress responses. Mechanistically, plant mTERFs transcend transcriptional termination, participating in transcriptional pausing, transcript stabilisation, intron splicing, and ribosome assembly. Advances in sequencing technologies have expanded the mTERF characterisation beyond model species to numerous agronomically relevant crops. This review summarises the primary advances in the characterisation of the mTERF gene family across plant species studied to date. It also highlights the most significant findings from their functional analysis and the molecular mechanisms by which specific mTERFs regulate chloroplast and mitochondrial gene expression. Furthermore, it underscores their crucial role in integrating organellar function with plant development and environmental adaptation.