Figure 6.

Evolution of the Barley Mla Complex.

Of the 34 predicted genes in the Mla region, 24 have at least one homolog. The RGH1 and CI2 families represent the major gene duplications in the region and account for 16% of the sequence. The remaining gene duplications have arisen from tandem fragment duplications, of which 14 are located in the 40-kb gene-rich tandem repeat and 2 are located in the 2.6-kb tandem repeat.

(A) DNA sequence similarities of RGH1bcd, CI2d, and CI2c compared with RGH1a, CI2f, and CI2e in the opposite orientation indicate an ancient inversion event followed by divergent evolution.

(B) A more recent duplication and inversion to create RGH1e is indicated by the higher sequence similarity between RGH1bcd and RGH1e than that between RGH1bcd and RGH1a (Table 1). Similarly, CI2a possesses the highest sequence similarity with CI2b within the CI2 family (Table 2).

(C) Within the last 3 million years, extensive transposon insertions in addition to repeat propagation increased the size of the region approximately threefold.

(D) A 40-kb tandem duplication of the region containing RGH1e, RGH2a, and RGH3a is the most recent addition to the present-day Mla region.

Genes are shown in rectangles with different colors representing different families, and transposable elements are designated by triangles. Designated colors match those in Figures 1 and 3 for each element. + indicates forward strand transcription, and − designates complementary strand transcription.