image: The focal emitter plant (Phytolacca americana) releases both constitutive (CPVs) and herbivore‑induced (HIPVs) volatiles. In a multi‑species system, a neighboring receiver plant perceives these volatile cues. This perception typically does not induce strong direct defense induction; instead, it primes the receiver for future attack. When herbivore attack subsequently occurs, the primed plant mounts a faster and stronger defense response, resulting in enhanced resistance across diverse receiver species. This primed state is accompanied by the upregulation of Ca²⁺ signaling genes (CML). Importantly, the effectiveness of this entire process is determined more by chemical distance among species than by phylogenetic distance. The receiver plants including: Pame: Phytolacca americana, Paci: P. acinosa, Rjap: Reynoutria japonica, Snig: Solanum nigrum, Ntab: Nicotiana tabacum, Hann: Helianthus annuus, Ahyp: Arachis hypogaea, Sbic: Sorghum bicolor, Zmay: Zea mays.
Credit: ©Science China Press
Plants are constantly releasing volatile organic compounds (VOCs) into the air. Some are background hum; others are alarm bells. When a plant is attacked by herbivores, it releases a specific VOC blend that neighboring plants can detect and interpret as a warning. But not every plant can listen in. What determines whether one plant can understand another’s chemical message? A new study led by researchers at Fudan University finds that the answer lies not in evolutionary kinship, but in the similarity of VOC profiles. The findings reshape our understanding of how plants communicate across species and offer a potential roadmap for designing more pest-resilient agricultural systems.
The team exposed nine plant species from six families to volatile emissions from Phytolacca americana, a globally invasive plant that has become widespread across China. They tested two types of defensive strategies: direct defense induction, which triggers immediate chemical responses upon detection of a threat, and defense priming, a “standby” mode that enables plants to mount faster, stronger responses only when an actual attack occurs.
Their results showed that defense priming was the dominant responding strategy across most receiver species. Primed plants exhibited stronger resistance to Spodoptera litura, a generalist herbivore that attacks a wide range of crops. This enhanced resistance was reflected in reduced oviposition by female moths, decreased larval feeding preference, and suppressed larval growth on primed plants. At the molecular level, the expression of defense-related genes, particularly Calmodulin-like (CML) genes, was significantly up‑regulated in primed plants. Importantly, the magnitude of this response varied dramatically across species. The key predictor was not how closely related the species were, but how similar their VOC profiles were—what the researchers call chemical distance.
“Plants with very different VOC profiles are like speakers of different dialects,” explains Professor Li. “Even when they are shouting an urgent warning, their neighbors simply cannot understand it. But plants with similar VOC profiles, even if they are evolutionarily distant, can effectively convey the message.”
The researchers also found that this signaling system is not solely triggered by herbivore attack. Unattacked plants continuously release the constitutive VOC blends, and neighboring plants appear to monitor these background emissions and adjust their defense readiness accordingly. This suggests that plant-plant communication is not a sporadic emergency response but an ongoing process of environmental surveillance.
Currently, how interspecific chemical communication shapes plant communities remains poorly understood. But these findings open new avenues: if species with similar VOC profiles can be identified and strategically paired, it may become possible to design agricultural and forestry systems that harness natural communication networks to enhance pest resistance, potentially reducing the reliance on chemical pesticides and fostering more sustainable crop protection strategies.
Journal
Science China Life Sciences
Method of Research
Experimental study