Plant-Plant Communication: Is There a Role for Volatile Damage-Associated Molecular Patterns?

Abstract

Damage-associated molecular patterns (DAMPs) are an ancient form of tissue-derived danger or alarm signals that initiate cellular signaling cascades, which often initiate defined defense responses. A DAMP can be any molecule that is usually not exposed to cells such as cell wall components, peptides, nucleic acid fragments, eATP and other compounds. DAMPs might be revealed upon tissue damage or during attack. Typically, DAMPs are derived from the injured organism. Almost all eukaryotes can generate and respond to DAMPs, including plants. Besides the molecules mentioned, certain volatile organic compounds (VOCs) can be considered as DAMPs. Due to their chemical nature, VOCs are supposed to act not only locally and systemically in the same plant but also between plants. Here, we focus on damage-induced volatiles (DIVs) that might be regarded as DAMPs; we will review their origin, chemical nature, physiochemical properties, biological relevance and putative function in plant-plant communications. Moreover, we discuss the possibility to use such airborne DAMPs as eco-friendly compounds to stimulate natural defenses in agriculture in order to avoid pesticides.

Keywords: DAMP; defense; plant–plant communication; signaling; volatiles; wounding.

FIGURE 1

Representative damage-induced volatiles (DIVs). Shown are structures and the biosynthetic origin (indicated by different colors) of the main DIVs involved in defense response induction (↑) and released after wounding or mechanical damage only. Compounds of the oxylipin pathway appear early within seconds to minutes, other compounds later within minutes to hours.

FIGURE 2

Scheme of the relationship between groups of volatile compounds induced upon herbivore feeding and tissue damage. Herbivore feeding provides chemical signals, HAMPs (herbivory-associated molecular patters), and causes tissue damage, which in turn generates DAMPs (damage-associated molecular patters). The combination of HAMPs and DAMPs induce the emission of HIPVs (herbivory-induced plant volatiles), which all belong to the huge group of VOCs (volatile organic compounds) that includes GLV (green leaf volatiles), terpenes and aromatic compounds. DAMPs are also generated by tissue damage/wounding alone. DIVs (damage-induced volatiles) represent a sub-group of DAMPs, due to their volatile character; all DIVs belong to HIPVs. For simplicity damage-induced electrical signals are neglected.

FIGURE 3

Model of damage-induced volatile (DIV) emissions that trigger intra- and interspecific defense responses in plants. Upon wounding events without contribution from other organisms, plants release specific DIVs possessing the ability to upregulate molecular and chemical defense mechanisms within the same individual as well as in neighboring plants up to a distance of 1 m. The signal intensity and distance of DIVs is highly dependent on environmental factors such as tropospheric reagents (ozone), temperature, radiation as well as the direction of airflow. All of the aforementioned conditions can drastically reduce the effectiveness of DIV signaling by lowering it to a ∼20 cm radius.