Transient gene expression in western white pine using agroinfiltration

A method for transient gene expression was developed for western white pine (WWP, Pinus monticola Dougl. ex D.Don) using reporter gene uidA encoding β-glucuronidase (GUS). GUS was transiently expressed in cross sections of primary and secondary needles, cotyledons, and current and second year stems of WWP via vacuum-infiltration with Agrobacterium tumefaciens. Histochemical assays of cross sections of secondary needles showed stronger blue color indicating GUS expression at day 1 and 2 than on other days post agroinfiltration (dpa). GUS activity expressed inside WWP cells was confirmed using light microscopy. In fluorometric assays, GUS expression was high at 1 dpa and lasted until 4 dpa in detached secondary needles, while similarly high expression levels only lasted until 2 dpa in attached secondary needles then dropped significantly. Although the length of GUS-staining zones varied among different WWP organs and between growth and dormant seasons, all tested WWP tissues using the protocol had high levels of transient GUS expression. Thus, heterologous candidate genes or endogenous silencing can be expressed in various WWP tissues or organs using this agroinfiltration approach. The current protocol for efficient transient gene expression will aid functional genomics study of WWP and its pathogens and related conifer species.