Differential effects of tropomyosin paralogs on mitochondrial dynamics in Saccharomyces cerevisiae

The actin cytoskeletal network is closely associated with mitochondria and performs crucial functions in mitochondrial movement, inheritance, and fission-fusion. Although its role in mitochondrial division is established, the specific contributions of actin-binding proteins (ABPs) remain unclear. Here, we report the role of tropomyosin, an ABP, in modulating mitochondrial morphology and dynamics. We demonstrate that loss of TPM1 and TPM2 in Saccharomyces cerevisiae differentially alters mitochondrial morphology. Tpm1 deletion results in fragmented mitochondria, whereas Tpm2 deletion produces an elongated tubular morphology. Through live-cell imaging, we show the localization of both paralogs to mitochondria, providing direct evidence of their association with the organelle. Microscopy-based analysis of fission-fusion frequencies revealed no change in the Tpm1 deletion, whereas Tpm2 deletion showed a decrease in these events, with a concomitant increase in the fusion factor Mgm1. Further, we characterized the overall health of mitochondria in the Tpm deletion mutants. Fragmented mitochondria in the Tpm1 deletion were hyperpolarized and exhibited increased mass and activity with elevated OCR, ATP levels, and basal ROS. In contrast, the tubular morphology of the Tpm2 deletion did not impair mitochondrial health. Overall, our findings suggest that Tpm modulates mitochondrial morphology and dynamics through its association with the actin cytoskeletal network.