Efficient polyethylene glycol (PEG) mediated transformation of the moss Physcomitrella patens

A simple and efficient method to transform Physcomitrella pantens protoplasts is described. This method is adapted from protocols for Physocmitrella protonemal protoplast and Arabidopsis mesophyll protoplast transformation. Due to its capacity to undergo efficient mitotic homologous recombination, Physcomitrella patens has emerged as an important model system in recent years. This capacity allows high frequencies of gene targeting, which is not seen in other model plants such as Arabidopsis. To take full advantage of this system, we need an effective and easy method to deliver DNA into moss cells. The most common ways to transform this moss are particle bombardment and PEG-mediated DNA uptake. Although particle bombardment can produce a high transformation efficiency, gene guns are not readily available to many laboratories and the protocol is difficult to standardize. On the other hand, PEG mediated transformation does not require specialized equipments, and can be performed in any laboratory with a sterile hood. Here, we show a simple and highly efficient method for transformation of moss protoplasts. This method can generate more than 120 transient transformants per microgram of DNA, which is an improvement from the most efficient protocol previously reported. Because of its simplicity, efficiency, and reproducibility, this method can be applied to projects requiring large number of transformants as well as for routine transformation.