A novel approach for pollen identification and quantification using
hybrid capture-based DNA metabarcoding
Abstract
Efforts to explore optimal molecular methods for identifying plant
mixtures, particularly pollen, are increasing. Pollen identification
(ID) and quantification is important in many fields, including
pollination ecology and agricultural sciences, but quantifying mixture
proportions remains challenging. Traditional pollen ID using microscopy
is time-consuming, requires expertise, and has limited accuracy and
throughput. Molecular barcoding approaches being explored offer improved
accuracy and throughput. The common approach, amplicon sequencing,
employs PCR amplification to isolate DNA barcodes, but introduces
significant bias, impairing downstream quantification. We apply a novel
molecular hybridisation capture approach to artificial pollen mixtures,
to improve upon current taxon ID and quantification methods. The method
randomly fragments DNA, and uses RNA baits to capture DNA barcodes,
which allows for PCR duplicate removal, reducing downstream
quantification bias. Metabarcoding was tested using two reference
libraries constructed from publicly available sequences; the matK
plastid barcode, and RefSeq complete chloroplast references. Single
barcode-based taxon ID did not consistently resolve to species or genus
level. The RefSeq chloroplast database performed better qualitatively
but had limited taxon coverage (relative to species used here) and
introduced ID issues. At family level, both databases yielded comparable
qualitative results, but the RefSeq database performed better
quantitatively. A restricted matK database containing only mixture
species yielded sequence proportions highly correlated with input pollen
proportions, demonstrating that hybridization capture usefulness for
metabarcoding and quantifying pollen mixtures. The choice of reference
database remains one of the most important factors affecting qualitative
and quantitative accuracy.