What determines plant species diversity along the Modern Silk Road in the east?

Potential of plant DNA information in determining the provenance and identify of unknown victims

Determination of the personal identity of victims is particularly important for the settlement of criminal cases. Unfortunately, useful information for identification is not always available. We here propose that the particles (pollens) of some plants with specific geographical distributions extracted from human lung tissues contribute to further determining the provenance or long-term residence of unknown victims, thereby considerably narrowing the search scope of the victims. We collected lung tissues from 155 victims with diverse causes of death, extracted DNA from lung tissues, sequenced the DNA fragments of plants on the Illumina Hiseq platform, and barcoded the plant species using phylogenetic methods. Finally, 108 unique plant sequences were detected in 55 samples and identified to belong to 36 species in 32 genera of 29 families. These plants were predominantly insect-pollinated crops and ornamental plants. No significant difference was observed between male and female samples, between urban and rural samples, or among samples of different ages and different sample sizes. There were 16 samples with 21 wild plant species. The original sources of 15 samples were overlapped with the distribution regions of detected plants; 2 samples narrowed the original sources to 2 provinces, which were quite coincident with their source places; 1 sample had no overlapping with its victim source region. Although plant information was only found in one-third of the samples, we further demonstrated the great potential of plant eDNA in identifying the source of unnamed corpses in a real-world case. We used plant eDNA from lung tissues to explore the provenance of an unknown female corpse found in Beijing. The source place of this victim was narrowed to Guangdong and Guangxi provinces, and finally, we confirmed her true identity in the list of missing persons in Guangxi Province. In the presence of a well-covered local reference library, the plant species detected in the lungs can be accurately identified. In difficult criminal cases where physical evidence is relatively weak, plant DNA information may provide new clues. In conclusion, the plant particles trapped in the lungs are promising to help forensic experts narrow the search scope for the identity of unknown victims.