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Triosephosphate Isomerase Genes in Two Trophic Modes of Euglenoids (Euglenophyceae) and Their Phylogenetic Analysis
Author(s) -
SUN GUILING,
SHEN WANG,
WEN JIANFAN
Publication year - 2008
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.2008.00324.x
Subject(s) - biology , triosephosphate isomerase , phylogenetic tree , trophic level , gene , phylogenetics , evolutionary biology , computational biology , genetics , ecology
. Two different length cDNAs encoding triosephosphate isomerase (TIM) were identified in the two trophic modes of euglenoids, the phototrophic Euglena gracilis and Euglena intermedia and the saprotrophic Astasia longa . Sequence analyses and presequence prediction indicated that the shorter cDNA encodes a cytosolic TIM and the longer cDNA encodes a plastid TIM (pTIM). The typical presequence of the putative A. longa pTIM and the high sequence similarity between A. longa pTIM and E. gracilis pTIM imply that A. longa pTIM is targeted to plastids. Therefore, although the plastids of A. longa have lost the ability of photosynthesis, they might retain other TIM‐related function(s), such as glycolysis and the synthesis of isopentenyl diphosphate or fatty acids. Including the TIM sequences obtained by us from chlorophytes and rhodophytes, our phylogenetic analyses indicated that euglenoid TIMs group neither with TIMs of kinetoplastids, which share the nearest common ancestor with euglenoids, nor are closely related to TIMs of chlorophytes, which are considered to be the donors of euglenoid plastids through secondary endosymbiosis. Instead, they group with TIMs of rhodophytes. In addition, our amino acid sequence alignment and structure modeling showed that TIMs of euglenoids and rhodophytes share a unique 2‐aa insertion within their loop‐4 areas. Therefore, either tim convergent evolution or lateral gene transfer (more probably) might have occurred between euglenoids and rhodophytes after the divergence of euglenoids with kinetoplastids.