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Science 29 June 2007:
Vol. 316. no. 5833, pp. 1862 - 1866
DOI: 10.1126/science.1143986
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Review
Genome Plasticity a Key Factor in the Success of Polyploid Wheat Under Domestication
Jorge Dubcovsky* and
Jan Dvorak
Department of Plant Sciences, University of California, One Shields Avenue, Davis, CA 95616, USA.
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Fig. 1. Wheat spikes showing (A) brittle rachis, (B to D) nonbrittle rachis, (A and B) hulled grain, and (C and D) naked grain. (A) Wild emmer wheat (T. turgidum ssp. dicoccoides), (B) domesticated emmer (T. turgidum ssp. dicoccon), (C) durum (T. turgidum ssp. durum), and (D) common wheat (T. aestivum). White scale bars represent 1 cm. Letters at the lower right corner indicate the genome formula of each type of wheat. Gene symbols: Br, brittle rachis; Tg, tenacious glumes; and Q, square head. [Photos by C. Uauy]
[View Larger Version of this Image (73K GIF file)]
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Fig. 2. The origin and current distribution of wheat. The wheat production map was provided by Dave Hodson, CIMMYT (20). The solid line ovals in the inset indicate the putative geographic regions of origin of the cultivated forms, whereas the dotted red line indicates a southern center of domesticated emmer diversity. The approximate distributions of wild emmer and Ae. tauschii are indicated by dots, and that of wild einkorn by yellow shading (3). Numbers indicate archaeological sites where remains of domesticated cereals dating back more than 9000 years BP were found: 1, Tell Aswad; 2, Abu Hureyra; 3, Cafer Höyük; 4, Jericho; 5, Cayönü; 6, Nahal Hemar; and 7, Nevali Cori [from (2)].
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Fig. 3. DNA insertions and deletions in orthologous VRN2 regions from the Am genome of T. monococcum (AY485644) and the A genome of durum wheat variety Langdon (new sequence EF540321). These regions diverged 1.1 ± 0.1 My ago. The red lines connect orthologous regions (>96% identical). Arrows represent genes: red, orthologous; blue, ortholog absent; and violet, pseudogene. Rectangles represent repetitive elements in their actual nested structure: red, orthologous; blue, insertions after divergence; green, deletion in the opposite genome (yellow region); and black, not determined. Only 31% of the orthologous intergenic regions have not been replaced. [See SOM text for details.]
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Fig. 4. Decay of the proportion of conserved sequences [C(t)] in orthologous intergenic regions with divergence time. The upper and lower red curves were calculated with two independent decay rate constants (K1 and K2), and the blue curve with the average rate constant. The circle labeled A represents identical sequences at the initial time of divergence. The comparison between T. urartu and durum A genome PSR920 regions (circle B) was used to estimate K1 (upper red curve) (30). The comparison between einkorn and durum A genome VRN2 regions(circle C) was used to estimate K2 (lower red curve). Comparison of orthologous intergenic regions between wheat B genome (AY368673) and D genome (AF497474) GLU1 regions (circle D) (59). Comparison of orthologous intergenic regions between wheat (AF459639) and barley (AY013246) VRN1 regions (circle E) (41, 42). [See SOM text for details.]
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