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      On the Origin of the Non-brittle Rachis Trait of Domesticated Einkorn Wheat

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          Abstract

          Einkorn and emmer wheat together with barley were among the first cereals domesticated by humans more than 10,000 years ago, long before durum or bread wheat originated. Domesticated einkorn wheat differs from its wild progenitor in basic morphological characters such as the grain dispersal system. This study identified the Non-brittle rachis 1 ( btr1) and Non-brittle rachis 2 ( btr2) in einkorn as homologous to barley. Re-sequencing of the Btr1 and Btr2 in a collection of 53 lines showed that a single non-synonymous amino acid substitution (alanine to threonine) at position 119 at btr1, is responsible for the non-brittle rachis trait in domesticated einkorn. Tracing this haplotype variation back to wild einkorn samples provides further evidence that the einkorn progenitor came from the Northern Levant. We show that the geographical origin of domesticated haplotype coincides with the non-brittle domesticated barley haplotypes, which suggest the non-brittle rachis phenotypes of einkorn and barley were fixed in same geographic area in today’s South-east Turkey.

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          Distribution of wild wheats and barley.

          If we accept the evidence at face value, we are led to conclude that emmer was probably domesticated in the upper Jordan watershed and that einkorn was domesticated in southeast Turkey. Barley could have been domesticated almost anywhere within the arc bordering the fertile crescent. All three cereals may well have been harvested in the wild state throughout their regions of adaptation long before actual farming began. The primary habitats for barley, however, are not the same as those for the wheats. Wild barley is more xerophytic and extends farther downslope and into the steppes and deserts along the wadis. It seems likely that, while all three early cereals were domesticated within an are flanking the fertile crescent, each was domesticated in a different subregion of the zone. Lest anyone should be led to think the problem is solved, we wish to close with a caveat. Domestication may not have taken place where the wild cereals were most abundant. Why should anyone cultivate a cereal where natural stands are as dense as a cultivated field? If wild cereal grasses can be harvested in unlimited quantities, why should anyone bother to till the soil and plant the seed? We suspect that we shall find, when the full story is unfolded, that here and there harvesting of wild cereals lingered on long after some people had learned to farm, and that farming itself may have orig inated in areas adjacent to, rather than in, the regions of greatest abundance of wild cereals. We need far more specific information on the climate during incipient domestication and many more carefully conducted excavations of sites in the appropriate time range. The problem is far from solved, but some knowledge of the present distribution of the wild forms should be helpful.
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            Site of Einkorn Wheat Domestication Identified by DNA Fingerprinting

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              Sequencing of Chloroplast Genomes from Wheat, Barley, Rye and Their Relatives Provides a Detailed Insight into the Evolution of the Triticeae Tribe

              Using Roche/454 technology, we sequenced the chloroplast genomes of 12 Triticeae species, including bread wheat, barley and rye, as well as the diploid progenitors and relatives of bread wheat Triticum urartu, Aegilops speltoides and Ae. tauschii. Two wild tetraploid taxa, Ae. cylindrica and Ae. geniculata, were also included. Additionally, we incorporated wild Einkorn wheat Triticum boeoticum and its domesticated form T. monococcum and two Hordeum spontaneum (wild barley) genotypes. Chloroplast genomes were used for overall sequence comparison, phylogenetic analysis and dating of divergence times. We estimate that barley diverged from rye and wheat approximately 8–9 million years ago (MYA). The genome donors of hexaploid wheat diverged between 2.1–2.9 MYA, while rye diverged from Triticum aestivum approximately 3–4 MYA, more recently than previously estimated. Interestingly, the A genome taxa T. boeoticum and T. urartu were estimated to have diverged approximately 570,000 years ago. As these two have a reproductive barrier, the divergence time estimate also provides an upper limit for the time required for the formation of a species boundary between the two. Furthermore, we conclusively show that the chloroplast genome of hexaploid wheat was contributed by the B genome donor and that this unknown species diverged from Ae. speltoides about 980,000 years ago. Additionally, sequence alignments identified a translocation of a chloroplast segment to the nuclear genome which is specific to the rye/wheat lineage. We propose the presented phylogeny and divergence time estimates as a reference framework for future studies on Triticeae.
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                Author and article information

                Contributors
                Journal
                Front Plant Sci
                Front Plant Sci
                Front. Plant Sci.
                Frontiers in Plant Science
                Frontiers Media S.A.
                1664-462X
                04 January 2018
                2017
                : 8
                : 2031
                Affiliations
                [1] 1National Institute of Agrobiological Sciences , Tsukuba, Japan
                [2] 2Plant Breeding Institute, The University of Sydney , Cobbitty, NSW, Australia
                [3] 3The Institute for Cereal Crops Improvement, Tel Aviv University , Tel Aviv, Israel
                [4] 4Centre National de la Recherche Scientifique , Saint-André-de-Cruzières, France
                [5] 5Plant Germplasm Institute, Graduate School of Agriculture, Kyoto University , Kyoto, Japan
                [6] 6Global Crop Diversity Trust , Bonn, Germany
                [7] 7Institute of Crop Science, National Agriculture and Food Research Organization , Tsukuba, Japan
                Author notes

                Edited by: Paul Gepts, University of California, Davis, United States

                Reviewed by: Ahmad Arzani, Isfahan University of Technology, Iran; Guoxiong Chen, Chinese Academy of Sciences, China

                *Correspondence: Takao Komatsuda, takao@ 123456affrc.go.jp Mohammad Pourkheirandish, mohammad.pourkheirandish@ 123456sydney.edu.au

                Present address: Shun Sakuma, Faculty of Agriculture, Tottori University, Tottori, Japan

                This article was submitted to Plant Genetics and Genomics, a section of the journal Frontiers in Plant Science

                Article
                10.3389/fpls.2017.02031
                5758593
                29354137
                2362f2ba-e4be-409f-9d35-ea938a56b04e
                Copyright © 2018 Pourkheirandish, Dai, Sakuma, Kanamori, Distelfeld, Willcox, Kawahara, Matsumoto, Kilian and Komatsuda.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                History
                : 18 September 2017
                : 14 November 2017
                Page count
                Figures: 7, Tables: 0, Equations: 0, References: 49, Pages: 10, Words: 0
                Categories
                Plant Science
                Original Research

                Plant science & Botany
                agricultural origins,einkorn,wheat,non-brittle rachis,domestication
                Plant science & Botany
                agricultural origins, einkorn, wheat, non-brittle rachis, domestication

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