Recent advances in understanding the roles of PPR proteins in plant responses to biotic and abiotic stresses

Pentatricopeptide repeat (PPR) proteins, one of the largest families of RNA-binding proteins in higher plants, play essential roles in the post-transcriptional regulation of RNA metabolism in organelles. PPR proteins are predominantly localized in mitochondria and/or chloroplasts, and participate in various post-transcriptional processes, including RNA editing (C-to-U conversion), intron splicing, RNA stabilization, cleavage, and translation. Although the importance of PPR proteins in organellar biogenesis and plant development are well established, recent studies have revealed their critical roles in plant's response to biotic and abiotic stresses. In this review, recent advances in understanding how distinct subclasses of P- and PLS-class PPR proteins mediate organellar RNA metabolism and influence stress signaling networks in plant's response to biotic and abiotic stresses are summarized. In particular, this review focuses on their functional relevance in responses to drought, salinity, extreme temperatures, heavy metal stress response, as well as pathogen infection, with emphasis on mechanisms involving reactive oxygen species homeostasis and organelle-to-nucleus retrograde signaling. Furthermore, recent progress in the synthetic redesign of PPR motifs, which enables programmable RNA recognition, is discussed. These advances provide valuable insights into the regulatory roles of PPR proteins and highlight the potential applications of synthetic PPR systems as tools to improve plant performance and resilience to environmental stress in changing climate conditions.