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An Oxalyl-CoA Dependent Pathway of Oxalate Catabolism Plays a Role in Regulating
Calcium Oxalate Crystal Accumulation and Defending against Oxalate-Secreting
Phytopathogens in Medicago truncatula
#MMPMID26900946
Foster J
; Luo B
; Nakata PA
PLoS One
2016[]; 11
(2
): e0149850
PMID26900946
show ga
Considering the widespread occurrence of oxalate in nature and its broad impact
on a host of organisms, it is surprising that so little is known about the
turnover of this important acid. In plants, oxalate oxidase is the most well
studied enzyme capable of degrading oxalate, but not all plants possess this
activity. Recently, an Acyl Activating Enzyme 3 (AAE3), encoding an oxalyl-CoA
synthetase, was identified in Arabidopsis. AAE3 has been proposed to catalyze the
first step in an alternative pathway of oxalate degradation. Whether this enzyme
and proposed pathway is important to other plants is unknown. Here, we identify
the Medicago truncatula AAE3 (MtAAE3) and show that it encodes an oxalyl-CoA
synthetase activity exhibiting high activity against oxalate with a Km = 81 ± 9
?M and Vmax = 19 ± 0.9 ?moles min-1mg protein-1. GFP-MtAAE3 localization
suggested that this enzyme functions within the cytosol of the cell. Mtaae3
knock-down line showed a reduction in its ability to degrade oxalate into CO2.
This reduction in the capacity to degrade oxalate resulted in the accumulation of
druse crystals of calcium oxalate in the Mtaae3 knock-down line and an increased
susceptibility to oxalate-secreting phytopathogens such as Sclerotinia
sclerotiorum. Taken together, these results suggest that AAE3 dependent turnover
of oxalate is important to different plants and functions in the regulation of
tissue calcium oxalate crystal accumulation and in defense against
oxalate-secreting phytopathogens.
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