The genomic dispersal of phytochrome-regulated genes in pea
Eleven light-regulated pea genes, grouped into five different categories based on their photophysiological characteristics, are analyzed genetically. Restriction fragment length polymorphisms (RFLPs) are used to detect variation for these genetic loci and to compare the variation observed with an assortment of genetic markers using F2 progeny arrays. Linkage relationships are then determined that establish the intrachromosomal assignments of all but three of the genes examined. The study reveals that of the six putative Cab genes characterized, three are located near the Cab multigene complex previously assigned to chromosome 7, two are linked to one another are not associated with the Cab multigene cluster, and one is isolated from both of these gene sets. The first three genetic loci do belong to the same photophysiological group as Cab\ however, the latter belong to three different groups, and only one of these is the group containing Cab. Two of the other phytochrome-regulated genetic loci, one purported to encode cytochrome and the other seed lectin, differ in both function and light regulation, but map in relative proximity on chromosome 2. A third gene, which encodes an ATP kinase, is located on chromosome 3. Ferredoxin 1 is also isolated from other light- regulated genes in this study, serving as an important marker locus on chromosome 6. The only other "gene" under review was found to represent a 120 bp poly A-tract and was not investigated further. This project illustrates that light-regulated genes in pea appear throughout the genome, encoding a variety of products. The results parallel findings in other plant systems, as photosystem genes can occur in clusters as well as single, dispersed copies. Data from this study also support a revision of pea chromosome 7.