Phosphoglucose isomerase (EC 5.3.1.9) isozymes in diploid and tetraploid Polygala species: evidence for gene duplication and diversification

Abstract

Phosphoglucose isomerase (PGI, EC 5.3.1.9) isozymes were examined by electrophoresis in the three common British species of Polygala, the diploids P. serpyllifolia and P. calcarea and the tetraploid P. vulgaris. All three species share the most anodal band which is probably the form of the enzyme occurring in the plastids (PGI-1). Individuals of the two diploid species each have one further band, probably the cytosolic form of the enzyme (PGI-2), with two phenotypes in each species, one of which is common to both. Individuals of P. vulgaris have one, three or six PGI-2 bands and 10 different homozygous phenotypes were observed. The commonest phenotypes in most populations show three bands with a central heterodimeric band staining more intensely than the outer two bands. Although P. vulgaris is a predominantly seif-fertilising species with no vegetative spread, many populations or sub-populations consist almost entirely of three-banded phenotypes. This indicates that the three-banded phenotypes are "fixed heterozygotes" resulting from the duplication of the Pgi-2 locus in the tetraploid. Heterozygotes between different three-banded forms show six bands in which the staining intensities are consistent with random pairing of the subunits. Plants showing silencing of one of the duplicate alleles were found in two small isolated areas in West Glamorgan. The biochemical diversity produced by the multiplicity of enzyme morphs in the tetraploid P. vulgaris may have contributed to its success. It is the most common, widespread and ecologically wide-ranging species in the genus in Europe.

Evidence for the duplication of PGI genes in Dipcadi serotinum L. (Liliaceae)

“…2). This suggests that the PGI-1 isozymes are located in the plastids as also noted in other plant species Oeser, 1974, Schnarrenberger et a!., 1975;Weeden and Gottlieb, 1979, 1980a, 1980b, Gottlieb and Weeden, 1981Gottlieb, 1982;Lack and Kay, 1986). The PGI-1 zone is weakly stained in relation to the other zones and was not well resolved in the majority of individuals analysed; for this reason data from only 40 individuals are available.…”

“…3; individuals 1 to 7) show no differences between leaf extracts and soaked pollen isozymes ( fig. 4), indicating that these dimeric phenotypes are specified by two gene loci (Gottlieb, 1977;Gottlieb and Weeden, 1979;Weeden and Gottlieb, 1979;Lack and Kay, 1986) fig. 3; individuals 18 to 24).…”

Relationships and hybridization between British species of Polygala– evidence from isozymes

“…P. amarella shared common PGI and PGM bands with other species, but had unique monomorphic bands in LAP and SKD. Descriptions of the PGI banding patterns from P. serpyllifolia, P. calcarea and P. vulgaris are given by Lack & Kay (1986).…”

“…Isozymes have been used extensively to study variation and heterozygosity in plant species (Hamrick, Linhart & Mitton, 1979;Hamrick & Godt, 1990) including Polygala (Lack & Kay, 1986, 1987, 1988 and they have proved useful in testing hypotheses in plant sj'stematics, giving strong evidence of relationships (Gottlieb, 1984;Proctor, Proctor & Groenhof, 1989). The aims of this paper (1) to clarify, using isozymes, the relationships between the four British species of Polygala.…”

Genetics of cytosolic phosphoglucose isomerase (PGI) variation in the Amazonian tree Pseudobombax munguba (Bombacaceae)

“…Isozymes resolved in the less anodal zone have been reported as variant forms of cytosolic PGI in other plants (Gottlieb & Weeden, 1981). High levels of isozyme variability for cytosolic PGI are usually the result of a gene duplication (Adams & Allard, 1977;Gottlieb, 1977Gottlieb, , 1982Goldring et a!., 1985;Lack & Kay, 1986; The Genetical Society of Great Britain, Heredity, 76, 531-538. respectively). An interlocus heterodimer between PGI-2b and PGI-3a was not observed on most gels because of the overlap of the two homodimeric enzymes, but was visible on gels which ran for more than 5 h.…”