The rug3 locus of pea encodes plastidial phosphoglucomutase

Two cDNA clones were isolated from pea (Pisum sativum L.) and their deduced amino acid sequences shown to have significant homology to phosphoglucomut ases from eukaryotic and prokaryotic sources. The longer cDNA contained a p utative transit-peptide-encoding sequence, supporting the hypothesis that t he isolated clones represent the cytosolic and plastidial isoforms of phosp hoglucomutase in pea. Plastid protein import assays confirmed that the puta tive plastidial isoform was targeted to the plastid stroma where it was pro teolytically processed. Expression, co-segregation, linkage, and molecular analyses have confirmed that the rug3 locus of pea encodes plastidial phosp hoglucomutase. Mutations at this locus result in a near-starchless phenotyp e of the plant.