Contribution of two-dimensional electrophoresis of proteins to maritime pine genetics

Several investigations undertaken on maritime pine genetics using two-dimensional gel electrophoresis of megagametophyte, collected from germinated or non-germinated seed, needle, bud and pollen proteins, are reviewed in the present paper. Different extraction methods adapted to each tissue or organ allowed reproducible protein patterns to be obtained. Genetic studies deal with genetic diversity, differential genome expression and genome mapping. Using 16 protein loci, the allelic frequencies were scored and the mean genetic diversity and differentiation were estimated in 192 individuals from six different origins. Proteins whose expression is restricted to a single organ were shown to be more variable than unspecific proteins in a study comparing needle, bud and pollen proteins from 18 unrelated trees. The level of variability was slightly higher in the bud than that in the needle or the pollen. Moreover, larger proteins were shown to display more allelic diversity than proteins having a lower molecular weight. Ninety protein loci were found polymorphic in megagametophyte (haploid tissue) and were used to construct a linkage map containing 12 linkage groups. Twenty-seven and 17 protein loci showing Mendelian segregation in germinated seed megagametophyte and in needles of an F-2 progeny, respectively, were introduced in another linkage map containing 436 random amplified polymorphic DNA (RAPD) markers. These studies outline the usefulness of the two-dimensional gel electrophoresis technique in genetic studies of conifers.