Submitted to: Workshop Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 5/20/2004
Publication Date: 5/22/2004
Citation: Faris, J.D., Gill, B.S., Simons, K.J., Fellers, J.P., Trick, H.N. 2004. Positional cloning of the Q gene in wheat. International Triticeae Mapping Initiative Workshop Proceedings. May 22-25, 2004, Minneapolis, MN. 2004 Program Abstracts. p. 22.
Technical Abstract: The Q gene is largely responsible for the domestication of wheat because it confers the free-threshing character and influences a repertoire of other domestication-related traits such as glume shape and toughness, rachis fragility, spike length, and culm height. Using AFLP and mRNA differential display with overlapping chromosome deletion lines and bulked-segregant analysis, we saturated the genomic region containing Q with molecular markers and constructed a high-resolution genetic map of the region in a population of 930 gametes. A marker linked to Q at a distance of 0.7 cM was identified and used as a starting point for chromosome walking. A Triticum monococcum BAC library was used to assemble a BAC contig spanning the Q locus. Analysis of recombination data and fast neutron-induced deletion mutants delineated the Q gene to a 100 kb segment, which contained an open reading frame with a high degree of similarity to APETALA2 (AP2)-like genes. AP2 genes are known to play a central role in the regulation of floral homeotic gene expression, and therefore, AP2 was a likely candidate for Q. The AP2-like gene was PCR-amplified from the free-threshing cultivar Chinese Spring and from three independent EMS-induced speltoid mutants in the Chinese Spring background. Sequence analysis revealed that all three mutants had single base-pair substitutions within the AP2-like coding region compared to Chinese Spring, thus providing strong evidence that the AP2-like gene was Q. In addition, the cultivar Bobwhite was transformed with the AP2-like gene from Langdon durum under the native promoter. Some transgenic plants had speltoid spikes while others had very compact spikes. Expression analysis indicated that the transgene and the native AP2-like gene were silenced in the speltoid transgenics, and multiple copies of the AP2-like gene were expressed in the transgenics with compact spikes. This result agrees with earlier studies that showed Q is dosage dependant. Q is expressed at lower levels in leaves and stems compared to immature spikes, but it is expressed in the spikes at the same level for Chinese Spring (free-threshing) and T. dicoccoides (non free-threshing), which suggests no differences for promoter activity between Q and q. Comparison of the deduced amino acid sequences of the AP2-like gene from four free-threshing species (T. aestivum, T. turgidum, T. carthlicum, and T. dicoccum) and four non free-threshing species (T. monococcum, T. urartu, T. spelta, and T. dicoccoides) indicated only one amino acid that consistently differentiated between the free-threshing and the non free-threshing species. Now that we have isolated the Q gene, we will proceed to study its regulatory function and investigate the origin and evolution of domesticated wheat