Connection between CYTOCHROME c and the TOR pathway to regulate growth in Arabidopsis

CANAL, M VICTORIA; MANSILLA, NATANAEL; GRASS, DIANA; GONZALEZ, DANIEL H; WELCHEN, ELINA

Congreso; LVIII Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology Research; 2022

Mitochondrial respiration is essential for energy production in most living organisms. Cytochrome c (CYTc) is a soluble heme protein of the mitochondrial intermembrane space, delivering electrons to complex IV during the last step of aerobic cellular respiration. We previously reported that Arabidopsis thaliana plants with lower CYTc levels (cytc mutants) exhibit decreased biomass and alterations in carbohydrate metabolism, explained in part by differential regulation in gibberellin homeostasis. In this work, we used plants with changes in CYTc levels to explore possible connections between CYTc and the growth regulatory pathway represented by the Target of Rapamycin (TOR) kinase. Detailed analysis of cytc mutants revealed phenotypic similarities with mutants in RAPTOR, a central component of the TOR complex. These comprise delayed germination, decreased root and hypocotyl growth, and delayed vegetative development. We focused on studying the growth of cytc seedlings, to understand how these plants administrate their energy resources for growth. We analyzed non-phosphorylated and phosphorylated ribosomal S6 kinase protein (S6K and P-S6K) levels as a readout of the activation of the TOR pathway in cytc mutants. We observed that the levels of both versions of S6K are lower than in wild-type plants, suggesting that TOR activity is affected in cytc plants. In agreement, autophagy, a process that is typically inhibited by the TOR pathway, is increased in cytc mutants during normal growth and in the presence of external sugar supplementation. Related to this process, the total amino acids content is increased in cytc mutants, probably as an energy source for growth. Our results allowed us to speculate that, in addition to their central role in ATP production, plant mitochondria also act as signalling organelles, orchestrating growth and development through different regulatory pathways, in part represented by CYTc.