Monoterpenes Support Systemic Acquired Resistance within and between Plants

Area of Science:

• Plant pathology
• Plant biochemistry
• Chemical ecology

Background:

• Systemic acquired resistance (SAR) is a crucial plant defense mechanism.
• Salicylic acid (SA) is a key regulator of SAR.
• The role of volatile organic compounds (VOCs) in SAR is not fully understood.

Purpose of the Study:

• To investigate the role of VOCs in SAR.
• To identify specific VOCs involved in SAR signaling.
• To elucidate the mechanism of VOC-mediated plant-to-plant defense.

Main Methods:

• Gas chromatography-mass spectrometry (GC-MS) analysis of plant emissions.
• Headspace exposure of *Arabidopsis thaliana* to specific monoterpenes.
• Analysis of gene expression related to SA and SAR pathways.
• Mutant analysis (*geranylgeranyl reductase1*) to assess monoterpene biosynthesis role.

Main Results:

• SAR was strongly associated with monoterpene emissions, particularly α-pinene and β-pinene.
• Exposure to pinenes induced defense responses, reactive oxygen species (ROS), and SA/SAR-related gene expression, including *AZI1*.
• Pinene-induced resistance depended on SA and *AZI1*, but monoterpenes acted in parallel to SA.
• Mutants with reduced monoterpene biosynthesis were SAR-defective.
• Plant emissions containing pinenes and camphene induced defense in neighboring plants.

Conclusions:

• Monoterpenes, especially pinenes, promote SAR by acting through ROS and *AZI1*.
• Monoterpenes likely function as infochemicals, facilitating plant-to-plant defense signaling.
• VOCs play a significant role in the propagation of plant defense signals.