Studies on metabolism and perception of carlactone-related compounds

Abstract

Strigolactones （SLs）are plant hormones that regulate shoot branching as well as being known as rhizosphere signals for parasitic and symbiotic interactions.　In 2012, an SL-like molecule called carlactone （CL） was identified through the biochemical functional analysis of three enzymes, CAROTENOID CLEAVAGE DIOXYGENASE7 （CCD7）, CCD8, and DWARF27 （D27）, yet its natural occurrence in plant tissue was not proved.　Using a chemically synthesized stable isotope labeled CL as an internal standard we successfully identified CL as an endogenous metabolite both in rice and Arabidopsis by LC-MS/MS analysis.　Moreover, we proved bioconversion of CL into some SL molecules in rice, conclusively demonstrating that CL is an endogenous biosynthetic precursor for SLs.　In addition, we found that CL is converted into its carboxylated analog, carlactonic acid （CLA）, in a manner dependent on a cytochrome P450, MAX1.　We also identified a methyl esterified derivative of CLA, methyl carlactonoate （MeCLA）, as an endogenous SL-like molecule in Arabidopsis.　Intriguingly, among three CL-related molecules （CL, CLA, MeCLA）, only MeCLA could physically interact with the SL receptor protein, AtD14, suggesting that the methyl esterification step of CLA has a critical role to produce bioactive hormone compounds in the shoot branching inhibition pathway.