Genetic analysis of threshability and other spike traits in the evolution of cultivated emmer to fully domesticated durum wheat

Authors: SHARMA, JYOTI - North Dakota State University; RUNNING, KATHERINE - North Dakota State University; Xu, Steven; ZHANG, QIJUN - North Dakota State University; PETERS, AMANDA - North Dakota State University; SHARMA, SAPNA - North Dakota State University; MCCLEAN, PHILLIP - North Dakota State University; Faris, Justin

Submitted to: Molecular Genetics and Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2019
Publication Date: 3/18/2019
Citation: Sharma, J.S., Running, K.L., Xu, S.S., Zhang, Q., Peters, A.R., Sharma, S., McClean, P.E., Faris, J.D. 2019. Genetic analysis of threshability and other spike traits in the evolution of cultivated emmer to fully domesticated durum wheat. Molecular Genetics and Genomics. 294(3):757-771. https://doi.org/10.1007/s00438-019-01544-0.
DOI: https://doi.org/10.1007/s00438-019-01544-0

Interpretive Summary: Genetic mutations in genes governing wheat threshability were critical for domestication. Knowing when these genes mutated during wheat evolution will provide more insight into the domestication process. We studied the genetic basis of seed threshability and other traits in domestic durum wheat and the more primitive, non-free-threshing durum wheat relative known as cultivated emmer wheat. We found that three genes work in an additive manner to prohibit the seed from being easily threshed in cultivated emmer wheat. These genes work to produce thick, rigid glumes, which hold the wheat seed very tightly making it difficult to liberate the seed from the wheat head. Each of these genes underwent mutations roughly 9,000 years ago, which led to the formation of modern free-threshing types. One of the three genes, referred to as the Q gene, also influenced other important traits such as plant height and head length and shape. These findings provide further insight into the timeline and possible pathways of wheat domestication and evolution, which provides researchers with useful knowledge to devise novel strategies to improve wheat.

Technical Abstract: Genetic mutations in genes governing wheat threshability were critical for domestication. Knowing when these genes mutated during wheat evolution will provide more insight into the domestication process and lead to further exploitation of primitive alleles for wheat improvement. We evaluated a population of recombinant inbred lines derived from a cross between the durum variety Rusty and the cultivated emmer accession PI 193883 for threshability, rachis fragility, and other spike-related traits. Quantitative trait loci (QTL) associated with spike length, spikelets per spike, and spike compactness were primarily associated with known genes such as the pleiotropic domestication gene Q. Interestingly, rachis fragility was not associated with the Q locus, suggesting that this trait, usually a pleiotropic effect of the q allele, can be influenced by the genetic background. Threshability QTL were identified on chromosome arms 2AS, 2BS, and 5AL corresponding to the tenacious glume genes Tg2A and Tg2B as well as the Q gene, respectively, further demonstrating that cultivated emmer harbors the primitive non-free-threshing alleles at all three loci. Genetic analysis indicated that the effects of the three genes are mostly additive, with Q having the most profound effects on threshability, and that free-threshing alleles are necessary at all three loci to attain a completely free-threshing phenotype. These findings provide further insight into the timeline and possible pathways of wheat domestication and evolution that led to the formation of modern day domesticated wheats.