DUPLICATION OF ALDOLASE AND ESTERASE LOCI IN CICER (CICEREAE, ALEF)

The genetic control of fructose bisphosphate aldolase (ALDO, EC 4.1.2.13) and esterase (EST, EC 3.1.1.2) isozymes in Cicer was studied by starch gel electrophoresis. Fixed heterozygote enzyme phenotypes were observed in homozygous lines for both Aldo-1, Aldo-2 and Est-4, Est-5. Crosses between the individuals carrying different alleles of the duplicated genes gave rise to asymmetrically staining bands for both enzyme systems. Subcellular localization studies demonstrated that the products of duplicated aldolase loci are present in the plastids, whereas duplicated esterase isozymes were found in the cytosolic compartment. Selfing and crossing experiments revealed that there are two nuclear genes encoding the plastid specific ALDO isozymes (Aldo-1 and Aldo-2). Similarly, EST-4 and EST-5 isozymes are specified by two nuclear genes (Est-4 and Est-5). No linkage was found between any of the duplicated genes and the other isozyme loci examined in this study. Taxonomic distribution of both duplications was examined in the electrophoretic survey of the related species. Present evidence suggests that these duplications are unique and probably occurred only in this monophyletic tribe, Cicereae, since no duplication was reported in the related genera. No evidence for mutations silencing any of the duplicated copies was detected in the genus. Although the mechanism for duplications is not known, evidence for translocations in Cicer and the existence of a similar linkage between ALDO and EST isozymes in related genera indicate that both duplications may have arisen simultaneously via duplication of a chromosomal segment carrying the ancestral state of the genes.