Pyruvate‐sensitive AOX exists as a non‐covalently associated dimer in the homeothermic spadix of the skunk cabbage, Symplocarpus renifolius

Abstract

The cyanide-resistant alternative oxidase (AOX) is a homodimeric protein whose activity can be regulated by the oxidation/reduction state and by a-keto acids. To further clarify the role of AOX in the skunk cabbage, Symplocarpus renifolius, we have performed expression and functional analyses of the encoding gene. Among the various tissues in the skunk cabbage, SrAOX transcripts were found to be specifically expressed in the thermogenic spadix. Moreover, our data demonstrate that the SrAOX protein exists as a non-covalently associated dimer in the thermogenic spadix, and is more sensitive to pyruvate than to other carboxylic acids. Our results suggest that the pyruvatemediated modification of SrAOX activity plays a significant role in thermoregulation in the skunk cabbage.

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

“…It has also been shown that the sacred lotus, a dicot, expresses at least two AOX proteins lacking a conserved CysI, termed NnAOX1a and NnAOX1b, both of which have been suggested to be stimulated by succinate (Grant et al, 2009). Moreover, it has been demonstrated that skunk cabbage expresses a pyruvate-sensitive ENV type of AOX, SrAOX, in this thermogenic spadix (Onda et al, 2007). Interestingly, in contrast to these homoeothermic plants expressing a succinate-or pyruvate-sensitive AOX, it appears that both A. maculatum and S. guttatum possess pyruvateinsensitive constitutively active AOX proteins (i.e.…”

“…The separation of proteins on nonreducing SDS-polyacrylamide gels and transfer to polyvinylidene difluoride membranes was carried out as described previously (Onda et al, 2007). Monoclonal antibodies against Sauromatum guttatum AOX ( Elthon et al, 1989) were used in the western analysis.…”

“…Mitochondria were isolated according to the methods described previously (Moore et al, 1992;Albury et al, 2002). Respiratory activity was measured using a Clark-type electrode cuvette (Oxy 1; Hansatech Instrument) as described previously (Onda et al, 2007).…”

In the heat of the night – alternative pathway respiration drives thermogenesis in Philodendron bipinnatifidum

“…For example, AOX from thermogenic N. nucifera also shows significant redox insensitivity, and stimulation of AOX occurs via succinate rather than pyruvate (Grant et al, 2009). An AOX that is not redox regulated (Onda et al, 2007;Grant et al, 2009) but is controlled by effectors could provide greater control of AOX flux for the precise temperature control these plants achieve over a prolonged period. By contrast, AOX from S. guttatum, which does not thermoregulate but rather heats in a single burst (Meeuse, 1966;Meeuse & Raskin, 1988), is constitutively active (Crichton et al, 2005).…”

Functional Coexpression of the Mitochondrial Alternative Oxidase and Uncoupling Protein Underlies Thermoregulation in the Thermogenic Florets of Skunk Cabbage

“…This pathway is mediated by alternative oxidase (AOX) and is shared among plants, fungi, and nematodes (Berthold and Siedow, 1993;McIntosh, 1994;Day and Wiskich, 1995;Wagner and Krab, 1995;Moore et al, 2002;McDonald and Vanlerberghe, 2004;Clifton et al, 2006;McDonald and Vanlerberghe, 2006;Onda et al, 2007). The AOX of plant mitochondria accepts electrons from the ubiquinone pool and uses them to reduce oxygen to water, with no conservation of energy through proton gradient formation (Siedow and Umbach, 1995).…”