PHYLOGENETIC UTILITY OF THE NUCLEAR GENE ARGININE DECARBOXYLASE - AN EXAMPLE FROM BRASSICACEAE

Arginine decarboxylase (ADC) is an important enzyme in the production of putrescine and polyamines in plants. It is encoded by a single or l ow-copy nuclear gene that lacks introns in sequences studied to date. The rate of Ade amino acid sequence evolution is similar to that of nd hF for the angiosperm family studied. Highly conserved regions provide several target sites for PCR priming and sequencing and aid in nucleo tide and amino acid sequence alignment across a range of taxonomic lev els, while a variable region provides an increased number of potential ly informative characters relative to ndhF for the taxa surveyed. The utility of the Ade gene in plant molecular systematic studies is demon strated by analysis of its partial nucleotide sequences obtained from 13 representatives of Brassicaceae and 3 outgroup taxa, 2 from the mus tard oil clade (order Capparales) and 1 from the related order Malvale s. Two copies of the Adc gene, Adc1 and Adc2, are found in all members of the Brassicaceae studied to date except the basal genus Aethionema . The resulting Ade gene tree provides robust phylogenetic data regard ing relationships within the complex mustard family, as well as indepe ndent support for proposed tribal realignments based on other molecula r data sets such as those from chloroplast DNA.