Piecemeal mitochondrial degradation in plants: a coordination between mitochondrial dynamics and mitophagosome formation

Mitochondrial dynamics play critical roles in mitochondrial quality control to maintain mitochondrial function. In plants, mitochondria are typically discrete rather than networked, but how damaged mitochondrial contents can be efficiently removed remains unclear. In a recent study, we demonstrate that the plant-specific fission regulator ELM1, together with DRP3 and the autophagic adaptor SH3P2, orchestrates mitochondrial dynamics and mitophagosome assembly for piecemeal mitophagy under heat stress condition. Deficiency in mitochondrial fission activity delays mitophagosome formation and leads to an accumulation of megamitochondria that are partially sequestered by phagophore intermediates positive for ATG8 and NBR1. Further 3D electron tomography analysis reveals that phagophore fragments expand toward the constriction sites of the abnormal protrusions from the mitochondrial body. These findings highlight an unappreciated role of plant mitochondrial fission machinery in coupling with autophagy machinery for mitochondrial segregation and mitophagosome assembly, establishing a mechanistic framework for plant mitophagy in stress resilience.<b>Abbreviations</b> ATG, autophagy related; DRP3, dynamin related protein 3; ELM1, elongated mitochondria 1; HS, heat stress; NBR1, next to BRCA1 gene 1; SH3P2, SH3 domain-containing protein 2.