Green Leaf Volatile-Burst in Selaginella moellendorffii.

Area of Science:

• Plant biochemistry
• Plant defense mechanisms
• Evolutionary biology

Background:

• Green leaf volatiles (GLVs) are key plant defense compounds derived from fatty acids.
• GLV-burst, a rapid GLV production upon tissue damage, is common in seed plants but less studied in non-seed plants.
• Understanding GLV-burst in diverse plant lineages is crucial for plant defense research.

Purpose of the Study:

• To investigate the GLV-burst capacity across major non-seed plant groups: monilophytes, lycophytes, and bryophytes.
• To identify the genes responsible for GLV biosynthesis in the lycophyte model *Selaginella moellendorffii*.
• To explore the evolutionary history of GLV-related genes in plants.

Main Methods:

• Assessing GLV production in response to mechanical damage in monilophytes, lycophytes, and bryophytes.
• Genomic analysis of *Selaginella moellendorffii* to identify candidate genes encoding CYP74 enzymes.
• In vitro expression of recombinant proteins to determine enzymatic activity (allene oxide synthase, hydroperoxide lyase).
• Phylogenetic analysis of CYP74 genes across seed and non-seed plants.

Main Results:

• Monilophytes and lycophytes exhibited significant GLV-burst capabilities, while bryophytes showed limited capacity.
• A gene encoding hydroperoxide lyase (HPL) in *S. moellendorffii* was identified as responsible for GLV-burst.
• Phylogenetic analysis suggests independent acquisition of HPL in lycophytes and seed plants via CYP74 gene diversification.

Conclusions:

• Lycophytes and monilophytes possess functional GLV-burst pathways, expanding the known distribution of this defense mechanism.
• The HPL gene, critical for GLV production, likely evolved independently in lycophytes and seed plants.
• This study provides insights into the evolution of plant defense volatile biosynthesis.