Regulating biological activity in plants with carboxylesterases

Ester hydrolysis dramatically affects the chemical and biological activity of both xenobiotics and endogenous metabolites in plants. By drawing analogies with organic synthesis, de-esterification reveals functional groups which show novel bioactivity and can undergo subsequent chemical modification. Thus, classically parent esters are hydrophobic, membrane permeable precursors of carboxylic acids which show activity as toxins, signalling agents and pathway intermediates. In plants, a large number of proteins with carboxylesterase activity have been recruited to catalyse these apparently facile reactions. Thus, enzymes that selectively hydrolyse xenobiotic and natural product carboxylesters are derived from three distinct super-families and this is in addition to the many other hydrolases that show this as a secondary activity resulting from their ability to cleave amide and thioester bonds. In this review, the ability of carboxylesterases to control the bioactivity and transport of herbicides, plant signalling agents and secondary metabolites in plants will be considered and recent insights into the identity of the respective enzymes reviewed.