Untitled

Abstract

Soybean (Glycine max cv. Stevens) suspension cells were used to investigate the expression of the alternative oxidase (Aox) multigene family. Suspension cells displayed very high rates of cyanide-insensitive respiration, but Aox3 was the only isoform detected in untreated cells. Incubation with antimycin A, citrate, salicylic acid or at low temperature (10 degrees C) specifically induced the accumulation of the Aox1 isoform. Aox2 was not observed under any conditions in the cells. Increases in Aox1 protein correlated with increases in Aox1 mRNA. Treatment of soybean cotyledons with norflurazon also induced expression of Aox1. Reactive oxygen species (ROS) were detected upon incubation of cells with antimycin, salicylic acid or at low temperature, but not during incubation with citrate. Aox1 induction by citrate, but not by antimycin, was prevented by including the protein kinase inhibitor staurosporine in the medium. The results suggest that multiple pathways exist in soybean to regulate expression of Aox genes and that Aox1 specifically is induced by a variety of stress and metabolic conditions via at least two independent signal transduction pathways.

Alternative oxidase: an inter-kingdom perspective on the function and regulation of this broadly distributed 'cyanide-resistant' terminal oxidase

“…The AOX pathway might serve as an alternative system that uses electrons in place of the incapacitated cyt pathway, thereby allowing glycolysis and respiration to continue to meet the needs of the organism. In support of this hypothesis, loss of the cyt pathway (by chemical or genetic means) results in an induction of AOX expression in plants, fungi and protists (Djajanegara et al 2002;CastroGuerrero et al 2004;Juárez et al 2004).…”

“…Salicylic acid increases AOX1 expression in soybean (Djajanegara et al 2002), methyl salicylate increases AOX expression in tomato (Fung et al 2006), and ethylene and jasmonic acid increase AOX1a expression in tobacco (Ederli et al 2006).…”

“…This has been demonstrated by many studies using northern blots, real-time PCR or microarray technologies to examine patterns of gene expression under a wide variety of experimental and environmental conditions. AOX1 gene expression in tobacco and soybean can be influenced by intermediates of the tricarboxylate acid cycle; in particular, citrate, malate and 2-oxoglutarate (Vanlerberghe and McIntosh 1996;Djajanegara et al 2002;Gray et al 2004). This is not particularly surprising given that the reducing equivalents generated at several steps of the cycle are used by dehydrogenases to input energy into the mitochondrial ETC.…”

“…Inhibitors of respiratory complexes also influence AOX gene transcription. The complex III (cytochrome c oxidoreductase) inhibitor antimycin A increases the expression of AOX1 in tobacco (Vanlerberghe and McIntosh 1996), soybean AOX1 (Djajanegara et al 2002) and AOX1a in A. thaliana, but not AOX1b, AOX1c or AOX2 expression . The complex IV (COX) inhibitor potassium cyanide (KCN) increases the expression of corn AOX1a (Polidoros et al 2005), whereas the cytochrome bc 1 complex inhibitor SSF-126 increases AOX expression in the fungus Magnaporthe grisea (Yukioka et al 1998).…”

“…Low temperature (4À10 C) leads to an increase in the expression of AOX1a and AOX1b in rice and soybean AOX1 (Ito et al 1997;Djajanegara et al 2002). Osmotic stress in cowpea and ozone treatment of tobacco have also been shown to influence AOX expression (Ederli et al 2006;Costa et al 2007).…”