A pseudoenzyme enables indole biosynthesis in eudicot plants

Area of Science:

• Plant biochemistry
• Molecular biology
• Biomolecule synthesis

Background:

• Indole is a crucial plant biomolecule involved in amino acid synthesis, defense, and signaling.
• Known indole biosynthesis relies on indole-3-glycerol phosphate lyases, absent in core eudicots.

Purpose of the Study:

• To elucidate the alternative pathway for indole production in core eudicots.
• To identify the molecular mechanism behind free indole generation for plant defense and communication.

Main Methods:

• Investigated the role of tryptophan synthase subunits and their paralogs in indole biosynthesis.
• Analyzed the catalytic activity and allosteric regulation of TSB-like and TSA interactions.
• Examined the expression patterns of TSB-like genes in various plant species.

Main Results:

• Identified a novel pathway for indole production in core eudicots involving tryptophan synthase alpha (TSA) and a pseudoenzyme, TSB-like.
• TSB-like, a noncatalytic TSB paralog, allosterically activates TSA to produce free indole.
• TSB-like evolved from TSB through mutations in key catalytic residues.

Conclusions:

• The TSB-like/TSA interaction represents a general mechanism for free indole formation in plants.
• This pathway is crucial for indole-mediated plant defense and inter-plant communication.
• The discovery sheds light on plant adaptation and signaling mechanisms.