UTILITY OF THE MITOCHONDRIAL NAD4L GENE FOR ALGAL AND PROTISTAN PHYLOGENETIC ANALYSIS

Mitochondrial gene sequences, in contrast to their plastid counterpart s, have been rarely exploited for use in determining algal phylogeneti c relationships. Their utilization would prove advantageous particular ly for the assessment of evolutionary relationships among protistan li neages that include photosynthetic species and their colorless heterot rophic descendents that contain only a reduced plastid genome as well as ancestral nonphotosynthetic relatives. Recent studies that have exa mined mitochondrial protein (cox1, cox2, cob, and nad5) rather than ri bosomal RNA genes confirm that these algal sequences are sufficiently conserved to be used routinely in algal systematics. In this investiga tion, we sequenced the mitochondrial nad4L gene, encoding a small (ca. 99-amino acid) polypeptide subunit of the NADH dehydrogenase complex, from two chromophytic algae and an oomycete to determine its suitabil ity for use in determining algal and protistan evolutionary relationsh ips. Our analysis demonstrated that nad4L could clearly resolve these three organisms as a distinct clade, the stramenopiles, to the exclusi on of terrestrial plants/chlorophytes and eu-fungi. However, the posit ion of deeply rooted species within the stramenopiles proved tenuous a nd would best be examined in conjunction with the analysis of longer m itochondrial protein gene sequences.