INTRON SEQUENCES PROVIDE A TOOL FOR HIGH-RESOLUTION PHYLOGENETIC ANALYSIS OF VOLVOCINE ALGAE

摘要: Three nuclear spliceosomal introns in conserved locations were amplified and sequenced from 28 strains representing 14 species 4 genera of volvocalean green algae. Data derived the three different yielded congruent results nearly all cases. In pairwise comparisons, a spectrum taxon-specific sequence differences ranging complete identity to no significant similarity was observed, with most distantly related organisms lacking any elements apart exon-intron boundaries pyrimidine-rich stretch near 3′ splice site. A metric (SI50), providing measure degree pair intron sequences, defined used calculate phylogenetic distances between whose displayed statistically similarities. The rate sequences divergence great enough provide useful information about relationships among geographical isolates single species, but cases too reliable guides above level. substitution approximately 3 × 10−8 per position year estimated, which is 150-fold higher than genes encoding rRNA 10-fold synonymous protein-coding regions. Thus, these homologous not only intraspecific relationships, also illustrate concept that parts gene may be subject extremely intensities selection. data generated here (1) reliably resolve for first time five extensively studied Volvox, (2) reveal two other Volvox more closely had previously been suspected, (3) confirm prior evidence particular Eudorina elegans Pleodorina illinoisensis appear sibling taxa, (4) contribute resolution several hitherto unsettled issues Chlamydomonas taxonomy.