Identification of a Gene for Pyruvate-Insensitive Mitochondrial Alternative Oxidase Expressed in the Thermogenic Appendices in Arum maculatum      

Abstract

Heat production in thermogenic plants has been attributed to a large increase in the expression of the alternative oxidase (AOX). AOX acts as an alternative terminal oxidase in the mitochondrial respiratory chain, where it reduces molecular oxygen to water. In contrast to the mitochondrial terminal oxidase, cytochrome c oxidase, AOX is nonprotonmotive and thus allows the dramatic drop in free energy between ubiquinol and oxygen to be dissipated as heat. Using reverse transcription-polymerase chain reaction-based cloning, we reveal that, although at least seven cDNAs for AOX exist (AmAOX1a, -1b, -1c, -1d, -1e, -1f, and -1g) in Arum maculatum, the organ and developmental regulation for each is distinct. In particular, the expression of AmAOX1e transcripts appears to predominate in thermogenic appendices among the seven AmAOXs. Interestingly, the amino acid sequence of AmAOX1e indicates that the ENV element found in almost all other AOX sequences, including AmAOX1a, -1b, -1c, -1d, and -1f, is substituted by QNT. The existence of a QNT motif in AmAOX1e was confirmed by nano-liquid chromatography-tandem mass spectrometry analysis of mitochondrial proteins from thermogenic appendices. Further functional analyses with mitochondria prepared using a yeast heterologous expression system demonstrated that AmAOX1e is insensitive to stimulation by pyruvate. These data suggest that a QNT type of pyruvate-insensitive AOX, AmAOX1e, plays a crucial role in stage-and organ-specific heat production in the appendices of A. maculatum.

Alternative NAD(P)H dehydrogenase and alternative oxidase: Proposed physiological roles in animals

“…Alternative respiratory enzymes can also be used by plants and fungi for multiple purposes not directly related to electron transfer. For instance, some plants use AOXs for thermogenesis (Watling et al, 2006;Onda et al, 2008;Ito et al, 2011), and/or adaptation to stresses (Saha et al, 2016;Vanlerberghe et al, 2016;Dahal & Vanlerberghe, 2017). The role of alternative RS enzymes in the regulation of ATP synthesis has also been proposed (Fernie et al, 2004).…”

Overexpression of an alternative oxidase gene, OsAOX1a, improves cold tolerance in Oryza sativa L.

“…AOX was 1st identified in the floral part of the thermogenic plant Araceae as a temperature-regulating protein (Ito et al, 2011); however, functional studies on cold tolerance are rare relative to those on other abiotic stresses. The little evidence that is available has been obtained using the model dicot species Arabidopsis.…”

The biochemical basis for thermoregulation in heat-producing flowers

“…Florets were detached from the spadices and used for the preparation of mitochondria. Purification was performed as previously reported 23 , with the exception that protease inhibitors (cOmplete ULTRA tablets (Roche), or 10 μM E-64 and 0.5 mM 4-(2-Aminoethyl) benzenesulfonyl fluoride hydrochloride) were added upon initiation of the grinding of the florets.…”