Triticeae

Triticeae is a tribe within the Pooideae subfamily of grasses that includes genera with many domesticated species. Major crop genera are found in this tribe including wheat (See Wheat taxonomy), barley, and rye; crops in other genera include some for human consumption and others used for animal feed or rangeland protection. Among the world's cultivated species this tribe has some of the most complex genetic histories. An example is bread wheat, which contains the genomes of three species, only one of them originally a wheat Triticum species. Seed storage proteins in Triticeae are implicated in various food allergies and intolerances.

Triticeae Genera

This list of tribes broadly follows that in Grass Genera of World. Although there are taxonomic disagreements about the precise circumscription of some genera, this scheme is typical of those used in taxonomic literature.

Cultivated or Edible Species

Aegilops

Amblyopyrum

Elmyus

Various species are cultivated for pastoral purposes or to protect fallow land from opportunistic or invasive species

Hordeum

Leymus

Secale

Triticum

Genetics

Triticeae and its sister tribe Bromeae (possible cultivars: Bromus mango S. America) when joined form a sister clade with Poeae and Aveneae (oats). Inter-generic gene flow characterized these taxa from the early stages. For example, Poeae and Aveneae share a genetic marker with barley and 10 other members of Triticeae, whereas all 19 genera of Triticeae bear a wheat marker along with Bromeae.^[2] Genera within Triticeae contain diploid, allotetraploid and/or allohexaploid genomes, the capacity to form allopolyploid genomes varies within the tribe. In this tribe, the majority of diploid species tested are closely related to Aegilops, the more distal members (earliest branch points) include Hordeum (Barley), Eremian, Psathyrostachys. The broad distribution of cultivars within the Tribe and the properties of the proteins have implication in the treatment of certain digestive diseases and autoimmune disorders.

Evolution of the Tribe

One of the earliest branches in Triticeae, to Psuedoroegeneria, produces the genome StSt and another Hordeum then genome = HH. Allotetraploid combinations of Psuedoroegeneria and Hordeum and are seen in Elmyus (HHStSt),^[3] but also shows introgression from Australian and Agropyron wheatgrasses.^[4] Elymus contains mostly Psuedoroegeneria mtDNA.^[5]

Many genera and species of Triticeae are exemplary of allopolyploids, having more chromosomes than seen in typical diploids. Typically allopolyploids are tetraploid or hexaploid, XXYY or XXYYZZ. The creation of polyploid species results from natural random events tolerated by polyploid capable plants. Likewise natural allopolyploid plants may have selective benefits and may allow the recombination of distantly related genetic material facilitating at a later time a reversion back to diploid. Poulard wheat is an example of a stable allotetraploid wheat.

The Secale (domesticated rye) may be a very early branch from the goat grass clad (or goat grasses are a branch of early rye grasses), as branch these are almost contemporary with the branching between monoploid wheat and Aegilops tauschii. Studies in Anatolia now suggest Rye (Secale) was cultivated, but not domesticated, prior to the holocene and to evidence for the cultivation of wheat. As climate changed the favorablitiy of Secale declined. At that time other strains of barley and wheat may have been cultivated, but humans did little to change them.

Goat Grasses and the Evolution of Bread Wheat

Tetraploidation in Wild Emmer Wheat

Aegilops appears to be basal to several taxa such as Triticum, Ambylopyrum, and Crithopsis. Certain species such as Aegilops speltoides could potentially represent core variants of the taxa. The generic placement may be more a matter of nomenclature. Aegilops and Triticum genera are very closely related as the image to the right illustrates the Aegilops species occupy most of the basal branch points in bread wheat evolution indicating that Triticum genus evolved from Aegilops after an estimated 4 million years ago.^[6] The divergence of the genomes is followed by allotetraploidation of a speltoid goatgrass x basal wheat species Triticum boeoticum with strains in the middle eastern region giving rise to cultivated emmer wheat.^[7]

Hexaploidation of tetraploid wheat

Hybridization of tetraploid wheat with Ae. tauschii produced a hulled wheat similar to spelt, suggesting T. spelta is basal. The tauschii species can be subdivided into subspecies tauschii (eastern Turkey to China or Pakistan) and strangulata (Caucasus to S. Caspian, N. Iran). The D genome of bread wheat is closer to A.t. strangulata than A.t. tauschii. It is suggested that Ae. tauschii underwent rapid selective evolution prior to combining with tetraploid wheat.

Wild Triticeae use by humans

Intense use of wild Triticeae' can be seen in the Levant as early as 23,000 years ago.^[8] This site, Ohala II (Israel), also shows that Triticeae grains were processed and cooked.^[9] Many cultivars appear to have been domesticated in the region of the upper Fertile Crescent, Levant and central Anatolia.^[10]^[11] More recent evidence suggests that cultivation of wheat from emmer's wheat required a longer period with wild seeding maintaining a presence in archaeological finds.^[12]

Pastoral Grasses

Triticeae has a pastoral component that some contend goes back to the Neolithic period and is referred to as the Garden Hunting Hypothesis. In this hypothesis grains could be planted or shared for the purpose of attracting game animals so that they could be hunted close to settlements.

Today, rye and other Triticeae cultivars are used to grazing animals, particularly cattle. Rye grasses in the New World have been used to selectively for use as fodder, but also to protect grasslands without the introduction of invasive old world species.

Triticeae and health

Glutens (storage proteins) in the Triticeae tribe have been linked to gluten-sensitive diseases. While it was once believed that [oat]s carried similar potentials, recent studies indicate that most-oat sensitivity is the result of contamination. Triticeae glutens examines of the proteins of Triticeae, important in the link between gluten, gastrointestinal, allergic and autoimmune diseases^[13] Some of the recently discovered biochemical and immunochemical properties of these proteins suggest they evolved for protection against dedicated or continuous consumption by mammalian seed eaters.^[14]^[15] One recent publication even raises doubts about wheat's safety for anyone to eat^[16] Overlapping properties with regard to food preparation have made these proteins much more useful as cereal cultivars and a balanced perspective suggest a variable tolerance to Triticeae glutens reflects early childhood environment and genetic predisposition.^[17]^[18]^[19]^[20]

References

^ Eadie M (2004). "Ergot of rye-the first specific for migraine.". J Clin Neurosci 11 (1): 4–7. doi:10.1016/j.jocn.2003.05.002. PMID 14642357.
^ Kubo N, Salomon B, Komatsuda T, von Bothmer R, Kadowaki K (2005). "Structural and distributional variation of mitochondrial rps2 genes in the tribe Triticeae (Poaceae).". Theor Appl Genet 110 (6): 995–1002. doi:10.1007/s00122-004-1839-x. PMID 15754209.
^ Mason-Gamer R (2004). "Reticulate evolution, introgression, and intertribal gene capture in an allohexaploid grass.". Syst Biol 53 (1): 25–37. doi:10.1080/10635150490424402. PMID 14965898.
^ Liu Q, Ge S, Tang H, Zhang X, Zhu G, Lu B (2006). "Phylogenetic relationships in Elymus (Poaceae: Triticeae) based on the nuclear ribosomal internal transcribed spacer and chloroplast trnL-F sequences.". New Phytol 170 (2): 411–20. doi:10.1111/j.1469-8137.2006.01665.x. PMID 16608465.
^ Mason-Gamer R, Orme N, Anderson C (2002). "Phylogenetic analysis of North American Elymus and the monogenomic Triticeae (Poaceae) using three chloroplast DNA data sets.". Genome 45 (6): 991–1002. doi:10.1139/g02-065. PMID 12502243.
^ Dvorak J, Akhunov ED, Akhunov AR, Deal KR, and Luo MC (2006). "Molecular characterization of a diagnostic DNA marker for domesticated tetraploid wheat provides evidence for gene flow from wild tetraploid wheat to hexaploid wheat.". Mol Biol Evol. 23 (7): 1386–1396. doi:10.1093/molbev/msl004. PMID 16675504.
^ >Heun M, Schäfer-Pregl R, Klawan D, Castagna R, Accerbi M, Borghi B, and Salamini F (1997). "Site of Einkorn Wheat Domestication Identified by DNA Fingerprinting.". Science 278 (5341): 1312–1314. doi:10.1126/science.278.5341.1312.
^ Weiss E, Wetterstrom W, Nadel D, Bar-Yosef O (2004). "The broad spectrum revisited: evidence from plant remains.". Proc Natl Acad Sci U S A 101 (26): 9551–5. doi:10.1073/pnas.0402362101. PMID 15210984.
^ Piperno D, Weiss E, Holst I, Nadel D (2004). "Processing of wild cereal grains in the Upper Palaeolithic revealed by starch grain analysis.". Nature 430 (7000): 670–3. doi:10.1038/nature02734. PMID 15295598.
^ Lev-Yadun S, Gopher A, and Abbo S (2000). "(ARCHAEOLOGY:Enhanced:) The Cradle of Agriculture.". Science 288 (5471): 1602–1603. doi:10.1126/science.288.5471.1602. PMID 10858140.
^ Weiss E, Kislev ME, and Hartmann A (2006). "(Perspectives-Anthropology:) Autonomous Cultivation Before Domestication.". Science 312 (5780): 1608–1610. doi:10.1126/science.1127235. PMID 16778044.
^ Balter M (2007). "Seeking Agriculture's Ancient Roots". Science 316: 1830–1835. doi:10.1126/science.316.5833.1830. PMID 17600193.
^ Silano M, Dessì M, De Vincenzi M, Cornell H (2007). "In vitro tests indicate that certain varieties of oats may be harmful to patients with coeliac disease". J. Gastroenterol. Hepatol. 22 (4): 528–31. doi:10.1111/j.1440-1746.2006.04512.x. PMID 17376046.
^ Mamone G, Ferranti P, Rossi M, et al (2007). "Identification of a peptide from alpha-gliadin resistant to digestive enzymes: Implications for celiac disease". doi:10.1016/j.jchromb.2007.05.009. PMID 17544966.
^ Shan L, Qiao SW, Arentz-Hansen H, et al (2005). "Identification and analysis of multivalent proteolytically resistant peptides from gluten: implications for celiac sprue". J. Proteome Res. 4 (5): 1732–41. doi:10.1021/pr050173t. PMID 16212427.
^ Bernardo D, Garrote JA, Fernández-Salazar L, Riestra S, Arranz E (2007). "Is gliadin really safe for non-coeliac individuals? Production of interleukin 15 in biopsy culture from non-coeliac individuals challenged with gliadin peptides". Gut 56 (6): 889–90. doi:10.1136/gut.2006.118265. PMID 17519496.
^ Collin P, Mäki M, Kaukinen K (2007). "Safe gluten threshold for patients with celiac disease: some patients are more tolerant than others". Am. J. Clin. Nutr. 86 (1): 260; author reply 260–1. PMID 17616789.
^ Guandalini S (2007). "The influence of gluten: weaning recommendations for healthy children and children at risk for celiac disease". Nestlé Nutrition workshop series. Paediatric programme 60: 139–55. doi:10.1159/0000106366. PMID 17664902.
^ Bao F, Yu L, Babu S, et al (1999). "One third of HLA DQ2 homozygous patients with type 1 diabetes express celiac disease-associated transglutaminase autoantibodies". J. Autoimmun. 13 (1): 143–8. doi:10.1006/jaut.1999.0303. PMID 10441179.
^ Zubillaga P, Vidales MC, Zubillaga I, Ormaechea V, García-Urkía N, Vitoria JC (2002). "HLA-DQA1 and HLA-DQB1 genetic markers and clinical presentation in celiac disease". J. Pediatr. Gastroenterol. Nutr. 34 (5): 548–54. PMID 12050583.

Contents

Triticeae Genera

Cultivated or Edible Species

Aegilops

Amblyopyrum

Elmyus

Hordeum

Leymus

Secale

Triticum