MULTIPLE CDNAS OF WHEAT VOLTAGE-DEPENDENT ANION CHANNELS (VDAC) - ISOLATION, DIFFERENTIAL EXPRESSION, MAPPING AND EVOLUTION

The mitochondrial outer membrane of eukaryotic cells contains voltage- dependent anion channels (VDAC) also termed porins. Three cDNAs from w heat (Triticum aestivum) were isolated and sequenced (Tavdac 1-3). The y share 65% similarity of their amino acid sequences, and therefore th ey probably represent isoforms. The deduced amino acid sequence of one of the cDNAs was found to be identical to the purified VDAC protein f rom wheat mitochondria [8]. Secondary structure analysis of the deduce d amino acid sequences of the three vdac cDNAs revealed a characterist ic ct helix at their N-terminal and beta-barrel cylinders characterist ic of VDAC channels. The Tavdac cDNAs are differentially expressed in meristematic tissues. The transcript levels of Tavdac I in all wheat t issues 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 different ial expression of vdac genes in plants. The Tavdac genes have been map ped on the wheat genome. Tavdac I is located on the long arm of chromo some 5, Tavdac 2 on the long arm of chromosome 1 and Tavdac 3 on the l ong arm of chromosome 3. A phylogenetic reconstruction indicates that vdac genes underwent numerous duplication events throughout their evol ution. All duplications occurred after the separation of plants from a nimals and fungi, and no orthologous genes are shared among phyla. Wit hin plants, some of the vdac gene duplications probably occurred befor e the monocotydelon-dicotydelon split.