Non-destructive DNA extraction from herbarium specimens: a method particularly suitable for plants with small and fragile leaves.

Abstract

Protocols for DNA extraction from plants generally involve physical and chemical destruction of tissues. Use of these conventional methods precludes preservation of morphological information from herbarium specimens, especially for small plants with few leaves, and reduces the voucher value of specimens. Here, we developed a new, non-destructive DNA extraction protocol (Protocol 1) that only needs a small piece of leaf (< 25mm2) to obtain DNA suitable for DNA sequencing from fragile herbarium specimens. The protocol was very simple and rapid; an extraction buffer was placed on the leaf surface of an intact specimen for 30min at room temperature (20°C). The quality of extracted DNA was checked by PCR amplification of two standard plant DNA barcode regions, the maturase K gene (matK, ca. 850 bp) and the ribulose-1,5-bisphosphatecarboxylase/oxygenase gene (rbcL, ca. 550 bp), for 14 vascular plant species encompassing various taxonomic groups. The protocol retrieved sequences from 80.0% of specimens for matK and 46.2% of specimens for rbcL. Placing of the extraction buffer onto specimens did not cause any tears or deformation, but caused discoloration in some plants. To improve DNA yield for specimens incompatible with Protocol 1, we developed an alternative protocol for DNA extraction with minimally invasive destruction of specimens (Protocol 2). In this protocol, a cut leaf was immersed in the extraction buffer for 30min and stored subsequently in a fragment pocket on the specimen sheet. This alternative method retrieved matK sequences from 80.0% of specimens and rbcL sequences from 92.8% of specimens. The combination of Protocols 1 and 2 enabled us to obtain matK sequences from 90.0% of specimens and rbcL sequences form 92.8% of specimens. The new protocols facilitate the use of museum specimens for use of DNA of museum specimens while still preserving morphological information.