Abstract
Trithorax gene family is a major player in epigenetic activities. This family of proteins carries the SET domain (SET: Su (var)3-9, Enhancer-of-zeste and Trithorax), which has methyltransferase activity. The mission of this work aims to study the SET domain of a novel tomato (Solanum lycopersicum) trithorax (SlTX1). Arabidopsis trithorax (ATX1) was used to fish out homologous sequences from tomato genome. The predicted SlTX1 sequence was used to design overlapping primers to clone the SET domain. The clone was sequnces and deposited in the GenBank. After multiple alignment with homologs along the plant kingdom, the sequences were analyzed using Neighbor-Joining method and bootstrapped 500 times. The generated phylogenetic tree revealed two major clades; higher plants clade and moss clade. Consequently, the first clade sharply separated monocots from dicots into two clusters. The monocot clade showed tighter grouping of maize with sorghum than with rice. On the other hand, the dicot clade was further subdivided into smaller subclades. The SET domain of tomato SlTX1 was subclustered in one subclade with the grape ortholog. The current investigation illustrates the distinctiveness evolution of the SET domain among monocot and dicot plants. These attractive functional features would be valuable in future plant phylogeny.