Mechanisms and control of rapid genomic changes in flax

Abstract

Background and aims: The nuclear DNA of certain varieties of flax (Linum usitatissimum) can vary within a single generation when the plants are grown under specific environmental conditions. This review details the genomic variations that have been identified and associated with this environmental response.

Conclusions: The variation occurs across the whole spectrum of sequence repetition and has been shown to occur in the highly repeated, middle repetitive and low copy number sequences. Although the variation has been shown to be spread throughout the genome it does not occur at random, as similar molecular events have been shown to occur repeatedly. The changes in two labile regions in the nucleus, the ribosomal RNA genes and a site-specific insertion event, have been shown to occur within the period of vegetative growth and over a relatively short period of that growth. The gradual change in total nuclear DNA that has been described would then need to have arisen through an accumulation of changes occurring over the whole, or most of the, period of growth prior to flowering. The polymorphisms that result from these rapidly occurring genomic events have also been observed in many other flax and linseed varieties as well as in the wild progenitors of flax.

Fig. 1.

The relative positions of the primers used to follow the appearance of LIS-1 during growth of Pl under inducing conditions. Primers 1 and 2 only amplify a fragment if LIS-1 is absent, while primers 1 and 3, and 2 and 4 only amplify from sites where LIS-1 has been inserted.

Fig. 2.

Total nuclear DNA, rDNA and LIS-1 variation during growth. These data are a compilation of the nuclear DNA amount from Evans et al. (1966), rDNA variation from Cullis and Charlton (1981), and unpublished data for LIS-1 from Y. Chen and C. A. Cullis. The LIS-1 data represents the DNA isolated from six leaves equally spaced along the stem (1 being the lowest leaf and 6 being a leaf from the top of the stem at flowering) of a plant grown under inducing conditions that resulted in a small genotroph. As can be seen, by the fourth sample the leaves have become homozygous for the presence of LIS-1. A, Amplification using primers 1 and 2; B, amplification using primers 1 and 3; C, amplification using primers 2 and 4.