Carlactone is an endogenous biosynthetic precursor for strigolactones

Area of Science:

• Plant biology
• Hormone signaling
• Biochemistry

Background:

• Strigolactones (SLs) are crucial plant hormones regulating shoot branching and mediating symbiotic and parasitic interactions.
• SLs possess a characteristic tricyclic-lactone (ABC-ring) and methyl butenolide (D-ring) structure, bridged by an enol ether.
• Carlactone (CL) was previously proposed as a biosynthetic intermediate but lacked in vivo validation and direct identification in plant tissues.

Purpose of the Study:

• To definitively establish carlactone (CL) as an endogenous precursor in strigolactone (SL) biosynthesis.
• To investigate the in vivo conversion of CL to known SLs in rice.
• To determine the stereochemistry of endogenous CL and its role in SL production.

Main Methods:

• Chemical synthesis of (13)C-labeled carlactone (CL).
• In vivo feeding experiments using (13)C-labeled CL in rice dwarf10 mutants.
• Liquid chromatography-quadrupole/time-of-flight tandem mass spectrometry (LC-QTOF-MS/MS) for endogenous CL identification.
• Stereochemical analysis of synthesized and endogenous CL isomers.

Main Results:

• (13)C-labeled CL was converted in vivo to (-)-[(13)C]-2'-epi-5-deoxystrigol ((-)-2'-epi-5DS) and [(13)C]-orobanchol in rice.
• Endogenous CL was successfully identified and quantified in rice and Arabidopsis tissues.
• The absolute stereochemistry of endogenous CL was determined as (11R), matching the precursor stereochemistry of (-)-2'-epi-5DS.
• Only the (11R)-isomer of CL, not the (11S)-isomer, was converted to (-)-2'-epi-5DS in feeding experiments.

Conclusions:

• Carlactone (CL) is a naturally occurring, endogenous precursor in strigolactone (SL) biosynthesis.
• The conversion of CL to SLs is stereospecific, with the (11R)-configuration being essential.
• This study provides conclusive evidence for CL's role and stereochemical requirements in the SL pathway.