Characterization and functional investigation of an Arabidopsis cDNA encoding a homologue to the d-PGMase superfamily

An Arabidopsis thaliana cDNA (At-74) has been isolated that encoded an uncharacterized protein showing homology with members of the d-PGMase superfamily: cofactor-dependent phosphoglycerate mutases (d-PGM-ases) and the phosphatase domain of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (6PF2Kase/F2, 6Pase). Preliminary phylogenetic studies indicated that At-74 cDNA and its close homologue in Arabidopsis, At-74H, belong, however, to an equally distinct group. At-74 was ubiquitously expressed in vegetative organs and induced by glucose. The At-74 cDNA was overexpressed in A. thaliana to investigate its function, but this overexpression did not result in a clear phenotype. Enzymatic assays performed on At-74-overproducing transgenic plants or E. coli cells showed no increase in either the activities of cofactor-dependent and -independent phosphoglycerate mutases (i-PGMases) and F2,6Pase or that of acid phosphatases. The possible role of At-74 in plant metabolism was further investigated by carbon partitioning experiments with [U-(14)C] glucose and measurements of soluble sugars in both young leaves and roots. Two overexpressing At-74 lines showed a clear increase in glucose uptake. This paper introduces the At-74 homologue of the d-PGMase superfamily members and supports a possible role of At-74 in carbohydrate metabolism.