Reference "A central role for gamma-glutamyl hydrolases in plant folate homeostasis"

Reference ID

54982

Title

A central role for gamma-glutamyl hydrolases in plant folate homeostasis

Source

Plant J, 2010, vol. 64, pp. 256-266

Authors (7)

Akhtar-T-A	Orsomando-G
Mehrshahi-P	Lara-Nunez-A
Bennett-M-J	Gregory-J-F-3rd
Hanson-A-D

Abstract

Most cellular folates carry a short poly-gamma-glutamate tail, and this tail is
believed to affect their efficacy and stability. The tail can be removed by gamma-
glutamyl hydrolase (GGH; EC 3.4.19.9), a vacuolar enzyme whose role in folate
homeostasis remains unclear. In order to probe the function of GGH, we
modulated its level of expression and subcellular location in Arabidopsis
plants and tomato fruit. Three-fold overexpression of GGH in vacuoles caused
extensive deglutamylation of folate polyglutamates and lowered the total folate
content by approximately 40% in Arabidopsis and tomato. No such effects were
seen when GGH was overexpressed to a similar extent in the cytosol. Ablation of
either of the major Arabidopsis GGH genes (AtGGH1 and AtGGH2) alone did not
significantly affect folate status. However, a combination of ablation of one
gene plus RNA interference (RNAi)-mediated suppression of the other (which
lowered total GGH activity by 99%) increased total folate content by 34%. The
excess folate accumulated as polyglutamate derivatives in the vacuole. Taken
together, these results suggest a model in which: (i) folates continuously
enter the vacuole as polyglutamates, accumulate there, are hydrolyzed by GGH,
and exit as monoglutamates; and (ii) GGH consequently has an important
influence on polyglutamyl tail length and hence on folate stability and
cellular folate content.