The Rab7 subfamily across <i>Paramecium aurelia</i> species; evidence of high conservation in sequence and function

We examined sequence conservation and signatures of selection in Rab7 proteins across 11 <i>Paramecium aurelia</i> species, and determined the localization patterns of two <i>P. tetraurelia</i> Rab7 paralogs when expressed as GFP fusions in live cells. We found that, while there is a variable number of Rab7 paralogs per genome, Rab7 genes are highly conserved in sequence and appear to be under strong purifying selection across <i>aurelias</i>. Additionally, and surprisingly based on earlier studies, we found that two <i>P. tetraurelia</i> Rab7 proteins have virtually identical localization patterns. Consistent with this, when we examined the gene family of a highly conserved Rab binding partner across <i>aurelias</i> (Rab-Interacting Lysosomal Protein, or RILP), we found that residues in key binding sites in RILPs were absolutely conserved in 13 of 21 proteins, representing genes from 9 of the 11 species examined. Of note, RILP gene number appears to be even more constrained than Rab7 gene number per genome. <b>Abbreviation</b>: WGD: Whole genome duplication.