Two classes of Tousled-like kinases indicate two rounds of gene duplication

--Owusu, EO and Rivin, CJ

The three TLK genes of maize were originally mapped to three loci, 1.12, 4.05 – 4.06 and 5.02 – 5.03 on the 1995 UMC map (Helentjaris et al., MNL 69, 1995). Sequence data obtained from genomic and cDNA clones from inbred B73 indicate that the three maize Tousled-like kinases, designated zmTLK1, zmTLK2 and zmTLK3, fall into two classes. The zmTLK2 and zmTLK3 genes are 96% identical over their catalytic regions, while zmTLK1 shares only 83% identity in the same region. (The complete zmTLK cDNA sequence has now been deposited in Genbank, accession number AY496080).

To learn something about the origins of these genes, we asked whether the identical genes were found on the syntenous chromosome locations on chromosomes 1 and 5, or on the non-syntenous positions 1 and 4 or 4 and 5. Using the oat-maize hybrid lines developed by Dr. R. L. Phillips (Plant Physiol. 125:1216–1235, 2001) we mapped zmTLK1 to maize chromosome 1. The two nearly identical zmTLK2 and 3 genes were found on the non-syntenous positions on chromosomes 4 and 5. These positions suggest that the two different classes were present in the tetraploid maize ancestor, and that a second duplication occurred to create the closely related zmTLK2 and 3. This model is also supported by the finding that both classes of TLK genes are present in Z. luxurians, Z. diploperennis, Z. mays mexicana and Tripsacum dactyloides.