Studies of the role of tRNA-isopentenyl-transferases in the formation of cytokinins
Arabidopsis thalianaPhyscomitrella patensSaccharomyces cerevisiaeTRNA isopentyltransferasesCytokinin biosynthesis
Plant tRNA isopentenyltransferases (tRNA-IPT, EC 2.5.1.8) have two roles, modification of tRNA and contribution to cytokinin synthesis. tRNA-IPT is among the best studied of the tRNA-modifying enzymes, but little biochemical information is available and none for the plant enzymes. Therefore two sets of experiments were conducted. The first one aimed to determine the kinetics and substrate specificity of the tRNA-IPT AtIPT2 from the higher plant Arabidopsis thaliana. The second project aimed to study the role of IPTs from the moss Physcomitrella patens in the production of cytokinin hormones. In moss only tRNA-IPTs but no adenylate IPTs are present (Schwartzenberg et al.2007). Adenylate IPTs are the major source of cytokinins in higher plants. The moss also differs by having more tRNA-IPTs than any other organism known. The first goal was to determine if these IPTs actually modify tRNA, or if one or more are in fact cytokinin synthases. For these studies a yeast mutant (MT8) lacking the intrinsic IPT gene was used. The mutant was transformed with the IPT from P. patens. The tRNA obtained from MT8 was used for in vitro assays to study the substrate specificity of the Arabidopsis AtIPT2.