Nuclear PPR Proteins Mediate Rhythmic C-To-U Editing of Mitochondrial RNA in Maize and Rice

Mitochondrial activity must be tightly coordinated in plants to ensure that energy production is appropriately modulated in response to exogenous and endogenous signals. However, the underlying molecular mechanisms are largely unknown. Here, we investigated this issue by analysing the crosstalk between the nucleus and mitochondria mediated by pentatricopeptide repeat (PPR) proteins, which can regulate the proper function of mitochondrial electron transport chain complexes by affecting C-to-U editing of mitochondrial mRNA. More than 75% of PPR genes in maize (Zea mays) exhibited rhythmic expression, which changed in response to different light conditions. Analysis of mitochondrial RNA editing efficiency throughout the day identified editing sites displaying rhythmic variations, with many sites affecting protein function based on AlphaFold2 prediction. Notably, the peak phase of rhythmic RNA editing lagged behind that of PPR gene expression, suggesting that these two processes are tightly related. We also observed rhythmic expression of PPR genes and rhythmic editing of mitochondrial mRNA in rice (Oryza sativa). These findings suggest that PPR proteins might serve as integrators of environmental signals and transmit these signals to mitochondria by affecting RNA editing.