Arabidopsis Squalene Epoxidase 3 (SQE3) Complements SQE1 and Is Important for Embryo Development and Bulk Squalene Epoxidase

ABSTRACT The existence of multigenic families in the mevalonate pathway suggests divergent functional roles forpathway components involved in the biosynthesis of plant sterols. Squalene epoxidases (SQEs) are keycomponents of this pathway, and Squalene Epoxidase 1 (SQE1) has been identified as a fundamentalenzyme in this biosynthetic step. In the present work, we extended the characterization of the remainingSQE family members, phylogenetically resolving between true SQEs and a subfamily of SQE-like proteinsthatisexclusivetoBrassicaceae.FunctionalcharacterizationoftrueSQEfamilymembers,SqualeneEpox-idase2(SQE2)andSqualeneEpoxidase3(SQE3),indicatesthatSQE3,butnotSQE2,contributestothebulkSQE activity in Arabidopsis, with sqe3-1 mutants accumulating squalene and displaying sensitivity to ter-binafine. We genetically demonstrated that SQE3 seems to play a particularly significant role in embryodevelopment. Also, SQE1 and SQE3 both localize in the endoplasmic reticulum, and SQE3 can functionallycomplementSQE1.Thus,SQE1andSQE3seemtobetwofunctionallyunequalredundantgenesinthepro-motion of plant SQE activity in Arabidopsis.Key words: Arabidopsis, embryo development, MVA pathway, squalene epoxidase, sterol biosynthesisLaranjeira S., Amorim-Silva V., Esteban A., Arro´ M., Ferrer A., Tavares R.M., Botella M.A., Rosado A., andAzevedo H. (2015). Arabidopsis Squalene Epoxidase 3 (SQE3) Complements SQE1 and Is Important for EmbryoDevelopment and Bulk Squalene Epoxidase Activity. Mol. Plant. 8, 1090–1102.