A Comprehensive High-Quality DNA and RNA Extraction Protocol for a Range of Cultivars and Tissue Types of the Woody Crop Avocado

High-quality DNA and RNA forms the basis of genomic and genetic investigations. The extraction of DNA and RNA from woody trees, like avocado (Persea americana Mill.), is challenging due to compounds which interact with nucleic acids and influence separation. Previously reported methods of DNA and RNA extraction from avocado have issues of low yield, quality and applicability across different cultivars and tissue types. In the current study, methods have been optimised for high-quality DNA extraction from 40 avocado cultivars and RNA extraction from multiple tissue types, including roots, stem, leaves, flowers and fruits. The method is based on the modification of the cetyltrimethylammonium bromide buffer, centred around the specific optimisation of chemicals, such as sodium dodecyl sulphate, polyvinylpyrrolidone, sodium sulphite, polyethylene glycol and β-mercaptoethanol. The DNA extraction method yielded high-molecular weight DNA from the leaf tissue of 40 avocado cultivars belonging to Mexican, Guatemalan and West Indian avocado horticultural groups. The method was further optimised for RNA extraction from different avocado plant parts, enabling extraction using amounts as low as ~10 mg of starting material. The DNA and RNA extracted was successfully used for long- and short-read sequencing and gene expression analysis. The methods developed may also be applicable to other recalcitrant plant species.