Extracellular ssDNA from P. tobira Exerts Strong Insecticidal Activity on C. hesperidum

Beyond its function as a carrier of hereditary information, recent research has uncovered novel properties for extracellular DNA, including its role in the adaptation to the environment when released from plants. The secreted DNA has been shown to exert insecticidal effect against insect pests, which plays an adaptive role in plant-insect interactions, particularly in regulating populations of economically important sap-feeding insects. The molecular mechanisms behind this insecticidal effect are underinvestigated and remain largely unknown. Therefore, there is a need for more efforts in uncovering these mechanisms to better understand the plant-pest interactions, which would provide new insights into natural pest control strategies and inspire biotechnological applications. In the current work, we show that Pittosporum tobira (P. tobira) secretes single-stranded DNA (ssDNA) that exerts an insecticidal effect on Coccus hesperidum (C. hesperidum). We collected extracellular DNA from P. tobira leaves and tested its potential insecticidal effect by applying it to C. hesperidum, which is a well-known pest that causes damage to P. tobira. Our results reveal that the outermost layer of leaf cuticle of P. tobira predominantly contains single-stranded DNA of approximately 100 bases in length, originating from both chloroplast and nuclear genomes. This DNA exhibits pronounced insecticidal activity against C. hesperidum, with chloroplast-derived sequences significantly enriched compared to total DNA in intact plant cells. These findings suggest that the microevolution of the P. tobira nucleome and plastome contributed to the formation of extracellular DNA with insecticidal properties (eci-DNA) as part of its defence strategy against insect pests. Notably, the laboratory-developed ssDNA-based genetic zipper technology, designed for sustainable pest management, possesses characteristics similar to eci-DNA found in nature, highlighting a potential natural parallel to this biotechnological approach.