The Importance of Cardiolipin Synthase for Mitochondrial Ultrastructure, Respiratory Function, Plant Development, and Stress Responses in Arabidopsis

Abstract

Cardiolipin (CL) is the signature phospholipid of the mitochondrial inner membrane. In animals and yeast (Saccharomyces cerevisiae), CL depletion affects the stability of respiratory supercomplexes and is thus crucial to the energy metabolism of obligate aerobes. In eukaryotes, the last step of CL synthesis is catalyzed by CARDIOLIPIN SYNTHASE (CLS), encoded by a single-copy gene. Here, we characterize a cls mutant in Arabidopsis thaliana, which is devoid of CL. In contrast to yeast cls, where development is little affected, Arabidopsis cls seedlings are slow developing under short-day conditions in vitro and die if they are transferred to long-day (LD) conditions. However, when transferred to soil under LD conditions under low light, cls plants can reach the flowering stage, but they are not fertile. The cls mitochondria display abnormal ultrastructure and reduced content of respiratory complex I/complex III supercomplexes. The marked accumulation of tricarboxylic acid cycle derivatives and amino acids demonstrates mitochondrial dysfunction. Mitochondrial and chloroplastic antioxidant transcripts are overexpressed in cls leaves, and cls protoplasts are more sensitive to programmed cell death effectors, UV light, and heat shock. Our results show that CLS is crucial for correct mitochondrial function and development in Arabidopsis under both optimal and stress conditions.

Cardiolipin at the heart of stress response across kingdoms

“…Atcls mutants harbor some of the features of yeast and mammal CL-deficient cells, such as low abundance of CI/CIII supercomplexes and abnormal mitochondria with few cristae. 16,17 Moreover giant mitochondria were observed suggesting deficiency of the plant mitochondrial fusion/fission machinery, 16,17 confirming previous results obtained in animals and yeast. [18][19][20] More specifically it was found that CL plays a dominant role in mitochondrial fission through the major mitochondrial fission factor, DYNAMIN-RELATED PROTEIN3 (DRP3).…”

“…16 These reports highlight the central role of CL in maintaining mitochondrial structure and function in yeast, plants, and animals. However, in contrast to yeast crd1 mutant, Atcls seedlings are severely affected, both in their growth and their development, 16,17 suggesting a broader role for CL in plant cell functioning.…”

“…21 At elevated temperature, the yeast crd1 mutant exhibits various vacuolar defects, demonstrating the existence of a mitochondria-vacuole signaling pathway dependent on CL synthesis. 22 In the Arabidopsis cls mutant, the absence of CL leads to an important perturbation of mitochondrial metabolism, that results in an increase of the levels of tricarboxylic acid (TCA) derived compounds and amino acids, especially glycine and serine, indicating an alteration of the photorespiratory pathway 17 ( Fig. 1).…”

“…4 In cells from Barth syndrome patients, reduced CL content leads to mitochondrial dysfunction and pathological conditions. 14,15 Very recently, cls T-DNA insertion knockdown 16 and knockout 17 mutants have been characterized in Arabidopsis. Atcls mutants harbor some of the features of yeast and mammal CL-deficient cells, such as low abundance of CI/CIII supercomplexes and abnormal mitochondria with few cristae.…”

Cardiolipin or MTCH2 can serve as tBID receptors during apoptosis

“…Indeed, these mitochondria exhibited increased electron density with less and disorganized cristae (Figure 2e), which is in agreement with previously published results. [33][34][35][36][37] In addition to reduction in cyt c, we also observed a decrease in the protein level of MTCO1 (Figure 2b). A reduction in the amount of this labile protein suggests a defect in respiratory chain complex IV assembly.…”