Multiple cDNAs of wheat voltage-dependent anion channels (VDAC): Isolation, differential expression, mapping and evolution

Abstract

The mitochondrial outer membrane of eukaryotic cells contains voltage-dependent anion channels (VDAC) also termed porins. Three cDNAs from wheat (Triticum aestivum) were isolated and sequenced (Tavdac 1-3). They share 65% similarity of their amino acid sequences, and therefore they probably represent isoforms. The deduced amino acid sequence of one of the cDNAs was found to be identical to the purified VDAC protein from wheat mitochondria [8]. Secondary structure analysis of the deduced amino acid sequences of the three vdac cDNAs revealed a characteristic alpha helix at their N-terminal and beta-barrel cylinders characteristic of VDAC channels. The Tavdac cDNAs are differentially expressed in meristematic tissues. The transcript levels of Tavdac 1 in all wheat tissues is at least 2.5-fold higher than Tavdac 2 and Tavdac 3. Tavdac 2 has a low level of expression in all floral tissues whereas Tavdac 3 is highly expressed in anthers. This is the first report on differential expression of vdac genes in plants. The Tavdac genes have been mapped on the wheat genome. Tavdac 1 is located on the long arm of chromosome 5, Tavdac 2 on the long arm of chromosome 1 and Tavdac 3 on the long arm of chromosome 3. A phylogenetic reconstruction indicates that vdac genes underwent numerous duplication events throughout their evolution. All duplications occurred after the separation of plants from animals and fungi, and no orthologous genes are shared among phyla. Within plants, some of the vdac gene duplications probably occurred before the monocotydelon-dicotydelon split.

Cloning and chromosomal localization of a cDNA encoding a mitochondrial porin from Drosophila melanogaster

“…3. Comparison of the amino acid sequences of humanl (porin 31HL) [27], human2 (HVDAC2) [10], bovine [28], D. melanogaster (dmprot), yeast [29], N. crassa [7], two isoforms from potato (potato34 and potato36) [12] and two isoforms from wheat (wheatl and wheat2) [13] The open reading frame of D. melanogaster cDNA corresponds to a protein consisting of 279 amino acids. Its deduced molecular weight was 30 189 Da, in good agreement with that estimated by SDS-polyacrylamide gel electrophoresis (31 kDa [20]).…”

“…Sequence comparison in the database gave the following identity score in comparison with other known porins: HVDAC2 [10] (55.7%), porin 31HL [27,10] (51.8%), bovine [28] (52%), N. crassa [7] (30.3%), wheat [13] (28.6%), Zea mays [11] (26.9%), 34 kDa potato [12] (25.8%), S. cerevisiae [29] (24.6%), 36 kDa potato [12] (23.8%) and Dictyostelium discoides [30] (23.4%). In Fig.…”

“…Messina et alIFEBS Letters 384 (1996) [9][10][11][12][13] was reported by Ha et al [37]. They obtained a cDNA containing an open reading frame which is essentially the same as HVDAC2.…”

“…At least four different genes [9], two of which have shown to be transcribed [10], were identified in humans: interestingly the protein expressed by these two mRNAs in VDAC-null yeast showed a striking difference in the hexokinase-binding property, which was conserved only by one of them [10]. Also in plants, families or groups of porins were identified [ 11,13].…”

“…This possibility is strengthened by the recovery of porin yeast-null mutants characterized by an electrophysiologically novel pore-forming activity [14][15][16]. On the other hand, a differential tissue expression could be invoked, as shown in wheat [13]. The first discovered porin-deficient human patient shows a lack of porin in muscle but its presence in fibroblasts [17,18]: this may be due to damage to the tissue-specification genetic machinery.…”