Identification and functional analysis of a carlactonoic acid methyltransferase in Arabidopsis

Abstract

Strigolactones (SLs) are a group of plant hormones that regulate not only shoot branching but also various developmental processes in plants. Methyl carlactonoate (MeCLA) has been proposed to be a bioactive molecule because this compound could interact with the AtD14 receptor and rescue the SL-deficient mutants in Arabidopsis. We have recently identified a methyltransferase named CLAMT that converts carlactonoic acid (CLA), a biologically inactive biosynthetic intermediate, into MeCLA in Arabidopsis. Endogenous CLA levels were accumulated, but MeCLA levels were drastically reduced in the clamt mutants. The clamt mutants exhibited a hyper-branching phenotype. This phenotype was rescued by MeCLA but not CLA treatment, supporting the idea that the conversion of CLA to MeCLA is critical in producing the biologically active compound(s) in inhibiting shoot branching. Moreover, by using grafting, we demonstrated that carlactone and CLA are mobile from roots to shoots, but MeCLA is not. Our finding will accelerate the understanding of SL biosynthesis in plants.