Phylogenetic utility of the nuclear gene arginine decarboxylase: an example from Brassicaceae

Arginine decarboxylase (ADC) is an important enzyme in the production ofputrescine and polyamines in plants. It is encoded by a single or low-copynuclear gene that lacks introns in sequences studied to date. The rate ofAdc amino acid sequence evolution is similar to that of ndhF for theangiosperm family studied. Highly conserved regions provide several targetsites for PCR priming and sequencing and aid in nucleotide and amino acidsequence alignment across a range of taxonomic levels, while a variableregion provides an increased number of potentially informative charactersrelative to ndhF for the taxa surveyed. The utility of the Adc gene inplant molecular systematic studies is demonstrated by analysis of itspartial nucleotide sequences obtained from 13 representatives ofBrassicaceae and 3 outgroup taxa, 2 from the mustard oil clade (orderCapparales) and 1 from the related order Malvales. Two copies of the Adcgene, Adc1 and Adc2, are found in all members of the Brassicaceae studiedto data except the basal genus Aethionema. The resulting Adc gene treeprovides robust phylogenetic data regarding relationships within thecomplex mustard family, as well as independent support for proposed tribalrealignments based on other molecular data sets such as those fromchloroplast DNA.