Stability of transgene expression during vegetative propagation of protoplast-derived tall fescue (Festuca arundinacea Schreb.) plants

The expression of a beta-glucuronidase (GUS) transgene, under the control of the rice actin1 promoter and first intron, introduced via PEG-mediated transformation of protoplasts, has been followed through a number of generations of vegetative propagation (tillering) in the forage grass Festuca arundinacea. Gene expression was found to be particularly unstable during early generations of tillering, but more stable in the fourth or fifth tiller generation. Loss of transgene expression was not due to deletion of the transgene nor was it due to gross rearrangements in the transgene as demonstrated by Southern blot analysis of expressing and non-expressing tillers. Loss of transgene expression due to hypermethylation of the transgene promoter has been shown previously, but in this case it was not possible to detect differences in the methylation patterns of the coding and promoter regions of expressing and non-expressing tillers. The implications for screening of transgenic plants intended to be vegetatively propagated are discussed.