Metabolic interplay between cytosolic phospho<i>enol</i>pyruvate carboxylase and mitochondrial alternative oxidase in thermogenic skunk cabbage, <i>Symplocarpus renifolius</i>

Skunk cabbage (<i>Symplocarpus renifolius</i>) blooms in early spring and its inflorescence, referred to as the spadix, can produce enough heat to melt snow. Here, we investigated glycolytic carbon flow at the PEP branch-point in thermogenic spadices. Our analyses revealed that petals and pistils in thermogenic florets exhibited higher expression of <i>SrPEPC</i> and <i>SrAOX</i> transcripts than those of <i>SrPK, SrPEPCK</i>, and <i>SrPEPtase</i>. Moreover, enzymatic analyses showed high activities of PEPC in the extracts from thermogenic florets. Finally, mitochondria from thermogenic florets showed low respiratory activities when pyruvate was used as a substrate, although a significant malate-mediated cyanide-insensitive respiration was observed. Collectively, these results suggest that PEP metabolism, primarily catabolized by PEPC, plays a critical role in thermogenesis in <i>S. renifolius</i>.