Specific Sequences Involved In Genome Size Evolution In Flax CA Cullis

CA Cullis

Department of Biology, Case Western Reserve University, Cleveland, OH 44106-7080, USA
Back to Kews Plant Genome Size Meeting Papers


    The genomic structure involving the interspersion of repetitive sequences and the genic regions is complex. Flax, which has a very restricted proportion of dispersed intermediately repetitive DNA (probably representing the families of transposable elements) is a useful model for looking at the occurrence of genomic events resulting in this interspersion. This genome structure, allied to the response of the genome to environmental growth conditions, makes it possible to follow these events within and between generations. Genomic changes have been identified using restriction fragment length polymorphisms, random amplification of polymorphic DNAs, representational difference analysis, and by the characterization of a complex insertion. Natural flax populations are polymorphic at every one of these regions that have been tested. Both the ribosomal RNA genes and the appearance of an insertion event, LIS-1, have been followed during the growth of plants under a range of growth conditions. For LIS-1, it becomes homozygous before flowering and is always transmitted to all the progeny under some conditions. Under other conditions it is never transmitted to the next generation. Therefore the presence of the insertion under some conditions has the potential to be adaptive, even though it is difficult to demonstrate that such a response is indeed adaptive. Some of the components included in the complex insertion also highlight polymorphisms elsewhere in the genome, suggesting that these fragments are active in far-reaching, rapid stress-related genome restructuring.