Plant Mitochondria

Abstract

Plant mitochondria, like the mitochondria of other eukaryotes, originated from an endosymbiotic event and have retained their own genome. Over a billion years of evolution, most mitochondrial genes are laterally transferred to the nucleus. Consequently, most proteins required for mitochondrial biogenesis and activity are synthesised in the cytosol and imported via specific protein import machineries. Mitochondria are energy‐generating organelles that via electron transfer chain (ETC), create a proton gradient and generate adenosine triphosphate (ATP), the energy chemical used by the cell for numerous biochemical reactions. Energy production can come at a cost as reactive oxygen species (ROS) are generated as by‐product. Plant mitochondria have alternative ETC pathways to regulate mitochondrial ROS (mtROS) through modulating the rate of redox reactions, proton gradient and ATP production. Although excessive ROS can damage cellular components and lead to programmed cell death, mtROS also play an important role as signalling molecules. mtROS are involved in nucleus–mitochondria communications (anterograde–retrograde signalling), mitochondrial autophagy (mitophagy) and play a role in the plant response to various environmental stimuli. Considering the pivotal roles of mitochondria in energy generation and cellular signalling, perturbation of mitochondrial biogenesis and activity renders plants to be more susceptible to various stresses and ultimately compromises plant growth, development and reproduction. Key Concepts Plant mitochondria are small (1–2 μm long) rod‐shaped organelle that undergo frequent fusion and fission events. The plant mitochondrial inner membrane houses protein complexes involved in the electron transfer chain (ETC) that creates a proton‐motive gradient across the intermembrane space to drive the production of adenosine triphosphate (ATP) through ATP synthase. The majority of plant mitochondrial proteins (approximately 2000) are encoded in the nuclear genome, whereas the plant mitochondrial genome contains around 50 genes encoding for ETC subunits, mitoribosomal translation machinery and transfer ribonucleic acids (tRNAs). The abundance of mtROS produced by the ETC is proportionally linked with the efficiency and rate of electron transfer and ATP production. Plant mitochondria have alternative ETC pathways to modulate ROS homeostasis, proton gradient and ATP production. mtROS can damage mitochondrial macromolecules and ultimately organelle function but are also important signalling molecules in various pathways, including stress response and anterograde–retrograde signalling. The nucleus controls mitochondrial gene expression through anterograde signalling, yet the mitochondria can also influence nuclear gene expression through retrograde signalling. Disrupted plant mitochondrial function often causes enhanced sensitivity to a number of stresses, disrupted pollen development in cytoplasmic male sterility and affects normal plant growth and development.

Ascorbate synthesis as an alternative electron source for mitochondrial respiration: Possible implications for the plant performance

“…Although the mETC of plants shares similar features with the mETC of animal mitochondria, there are critical differences in composition and functions ( Møller et al., 2021 ). The classical view is that electrons from the matrix NADH oxidation in Complex I are transferred to the UQ, reducing it to UQH 2 , while protons are transported to the inter-membrane space (IMS) ( Møller, 2001 ; Ghifari and Murcha, 2020 ) ( Figure 4A ). Electrons from the oxidation of succinate to fumarate, which occurs through FADH 2 by succinate dehydrogenase, or simply by the mETC Complex II are also transferred via UQ ( Figure 4A ).…”