Figure 4.

Evolution of grass MLE transposases and accompanying intron gains. (a) Diversification of plant MLEs and possible intron gains during grass evolution. Relationships among grass taxa and estimated divergence times are from refs. 20 and 21. Uncertain divergence times are represented by dashed lines. MLE lineages detected in each taxa are shown by their respective capital letters. Arrowheads indicate the presence of a particular lineage before the divergence of the descending species. It was assumed that sequences from dicots and Iridaceae are related to lineage A of grasses, although this relationship was not strongly supported by bootstrap analysis (see Fig. 2). (b) Positions of introns in different grass MLE transposases. Introns are depicted as triangles. Numbers above or below the triangles refer to the position of coding nucleotides interrupted by the intron. The distribution and range of lengths for each type of intron are shown (see also Fig. 2).