A Previously Unknown Oxalyl-CoA Synthetase Is Important for Oxalate Catabolism in Arabidopsis

Abstract

Oxalate is produced by several catabolic pathways in plants. The best characterized pathway for subsequent oxalate degradation is via oxalate oxidase, but some species, such as Arabidopsis thaliana, have no oxalate oxidase activity. Previously, an alternative pathway was proposed in which oxalyl-CoA synthetase (EC 6.2.1.8) catalyzes the first step, but no gene encoding this function has been found. Here, we identify ACYL-ACTIVATING ENZYME3 (AAE3; At3g48990) from Arabidopsis as a gene encoding oxalyl-CoA synthetase. Recombinant AAE3 protein has high activity against oxalate, with K m = 149.0 6 12.7 mM and V max = 11.4 6 1.0 mmol/min/mg protein, but no detectable activity against other organic acids tested. Allelic aae3 mutants lacked oxalyl-CoA synthetase activity and were unable to degrade oxalate into CO 2 . Seeds of mutants accumulated oxalate to levels threefold higher than the wild type, resulting in the formation of oxalate crystals. Crystal formation was associated with seed coat defects and substantially reduced germination of mutant seeds. Leaves of mutants were damaged by exogenous oxalate and more susceptible than the wild type to infection by the fungus Sclerotinia sclerotiorum, which produces oxalate as a phytotoxin to aid infection. Our results demonstrate that, in Arabidopsis, oxalylCoA synthetase encoded by AAE3 is required for oxalate degradation, for normal seed development, and for defense against an oxalate-producing fungal pathogen.

A Formate Dehydrogenase Confers Tolerance to Aluminum and Low pH

“…In plants, various formate production pathways including photorespiration, glycolysis, cell wall synthesis, or degradation have been proposed (Igamberdiev et al, 1999;Hanson et al, 2000), but direct experimental evidence is limited. Recently, a previously unknown oxalyl-CoA synthetase, ACYL-ACTIVATING ENZYME3 (AAE3), was identified to be involved in oxalate degradation to form formate, which is further degraded by FDH in Arabidopsis (Foster et al, 2012). Furthermore, FDH is coexpressed with AAE3 and regulated by AAE3.…”

An Oxalyl-CoA Synthetase Is Involved in Oxalate Degradation and Aluminum Tolerance

“…The proposition of another pathway for oxalate catabolism can date back to 1961 (Giovanelli and Tobin, 1961), but the enzyme has not been discovered until recently. Foster et al (2012) characterized Arabidopsis ACYL-ACTIVATING ENZYME3 (AAE3) gene encoding an oxalyl-CoA synthetase that is capable of catalyzing the first step in the CoA-dependent pathway of oxalate catabolism. To date, oxalate oxidase was found only in monocots but seems absent in dicots, but oxalyl-CoA synthetase was reported to exist in Arabidopsis (Foster et al, 2012), Medicago truncatula (Foster et al, 2016), and yeast (Saccharomyces cerevisiae ;Foster and Nakata, 2014).…”

“…Foster et al (2012) characterized Arabidopsis ACYL-ACTIVATING ENZYME3 (AAE3) gene encoding an oxalyl-CoA synthetase that is capable of catalyzing the first step in the CoA-dependent pathway of oxalate catabolism. To date, oxalate oxidase was found only in monocots but seems absent in dicots, but oxalyl-CoA synthetase was reported to exist in Arabidopsis (Foster et al, 2012), Medicago truncatula (Foster et al, 2016), and yeast (Saccharomyces cerevisiae ;Foster and Nakata, 2014). While oxalate oxidase was found to be localized to the cell wall and oxalyl-CoA synthetase was localized in cytoplasm, both play a role in defending plants against oxalate-secreting fungal phytopathogens.…”

Regulating cytoplasmic oxalate homeostasis by Acyl activating enzyme3 is critical for plant Al tolerance

“…14 To date, AAE3 proteins from rice bean, Medicago truncatula, and Arabidopsis (Arabidopsis thaliana) have been characterized as oxalyl-CoA synthetases. 13,15,16 Here, amino acid sequence alignment revealed that AAE3 proteins from common buckwheat and amaranth display high identity with known AAE3 proteins, all having a conserved AMP binding domain and acetylCoA synthetase domain (Fig. 2).…”

“…Although the biochemical and molecular biological characterization of FeAAE3 and AhAAE3 proteins has to be investigated, it is reasonable to suggest that they also function as oxalyl-CoA synthetases. Given that AAE3 protein is characterized by having activities specific to oxalate, 13,15,16 the upregulation of AAE3 genes suggests that oxalate accumulates under Al stress.…”