Triticeae Genomics For Sustainable Agriculture

Triticeae is a botanical tribe within the subfamily Pooideae of grasses that includes genera with many domesticated species. Major crop genera found in this tribe include 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 with only one being a wheat ''Triticum'' species. Seed storage proteins in the Triticeae are implicated in various food allergies and intolerances.

Genera of Triticeae

Genera recognized in Triticeae according to Robert Soreng et al.:

*'' Aegilops''
*'' Agropyron''
*''Amblyopyrum''
*''Anthosachne''
*''Australopyrum''
*'' Connorochloa''
*''Crithopsis''
*''Dasypyrum''
*'' Douglasdeweya''
*'' Elymus'' (syn. ''Campeiostachys'', ''Elytrigia'', '' Hystrix'', ''Roegneria'', ''Sitanion'')
*''Eremopyrum''
*''Festucopsis''
*'' Henrardia''
*''Heteranthelium''
*''Hordelymus''
*''Hordeum'' (syn. '' Critesion'')
*''Kengyilia''
*'' Leymus'' (syn. '' Aneurolepidium'', '' Eremium'', '' Macrohystrix'', '' Microhystrix'')
*''Pascopyrum''
*'' Peridictyon''
*''Psathyrostachys''
*''Pseudoroegneria''
*''Secale''
*''Stenostachys''
*''Taeniatherum''
*''Thinopyrum''
*''Triticum''

Cultivated or edible species

''Aegilops''

*Various species (rarely identifiable to species in archaeological material) occur in pre-agrarian archaeobotanical remains from Near Eastern sites. Their edible grains were doubtless harvested as wild food resources.
* '' speltoides''
ancient food grain
putative source of B genome in bread wheat and G genome in ''T. timopheevii''
* '' tauschii'' - Source of D genome in wheat

''Amblyopyrum''

* ''muticum'' - Source of T genome.

''Elymus''

Various species are cultivated for pastoral purposes or to protect fallow
land from opportunistic or invasive species
* '' canadensis''
edible, bread-flour capable, fiddly seeds
* '' trachycaulus''
pastoral cultivar

''Hordeum''

Many barley cultivars
* '' vulgare'' - common barley (6 subspecies, ~100 cultivars)
* ''bulbosum''
edible seeds
* '' murinum'' (mouse barley)
cooked as piñole, bread-flour capable
medicinal: diuretic.

''Leymus''

* '' arenarius'' (Lyme grass)
bread-flour capable, possible food additive
* '' racemosus'' (Volga Wild Rye)
drought tolerant cereal, used in Russia
* '' condensatus'' (Giant Wild Rye)
Edible seeds, harvesting problematic small seeds
* '' triticoides'' (Squaw grass)
used in North America, seed hairs must be singed

''Secale''

Ryes
* '' cereale'' (Cereal Rye) - Livestock feed and sour dough bread - 6 subspecies.
* ''cornutum'' (spurred rye) - herbal medicine: ergot (ergot of spurred rye) at very low doses; dangerously toxic as food.
* ''strictum''
actively cultivated
* ''sylvestre'' - (Tibetan Rye)
actively cultivated
in Tibet and China highlands.
* ''vavilovii'' (Armenian Wild Rye)
edible seeds, thickener

''Triticum''

(Wheat)
* '' aestivum'' (bread wheat) - (AABBDD Genome)
** ''compactum'' (club wheat)
** ''macha'' (hulled)
** ''spelta'' (hulled, spelt)
** ''sphaerococcum'' (shot wheat)
* ''monococcum'' (Einkorn wheat) (A Genome)
* '' timopheevii'' (Sanduri wheat)
* ''turgidum'' (poulard wheat) (AABB Genome)
** '' carthlicum'' (Persian black wheat)
** ''dicoccoides'' (wild emmer wheat)
** '' dicoccum'' (cultivated emmer wheat) - used to make Farro
** '' durum'' (durum wheat)
** ''paleocolchicum''
** '' polonicum'' (Polish wheat)
** '' turanicum''

Genetics

Triticeae and its sister tribe ''Bromeae'' (bromes or cheat grasses) 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 mtDNA genetic marker with barley and 10 other members of Triticeae, whereas all 19 genera of Triticeae bear a wheat marker along with Bromeae.

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 ''Pseudoroegeneria'', produces the genome StSt and another ''Hordeum'' then genome = HH. Allotetraploid combinations of ''Pseudoroegeneria'' and ''Hordeum'' and are seen in ''Elmyus'' (HHStSt), but also shows introgression from Australian and Agropyron wheatgrasses. Elymus contains mostly ''Pseudoroegeneria'' mtDNA.

Many genera and species of Triticeae are allopolyploids, having more chromosomes than seen in typical diploids. Typical allopolyploids are tetraploid or hexaploid, XXYY or XXYYZZ. The creation of polyploid species results from natural random events tolerated by polyploid-capable plants. Natural allopolyploid plants may have selective advantages and some may permit the recombination of distantly related genetic material. 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

Tetraploidization in wild emmer wheat

''Aegilops'' appears to be basal to several taxa such as ''Triticum'', ''Amblyopyrum'', 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. Genera ''Aegilops'' and ''Triticum'' are very closely related; as the adjacent image illustrates, the ''Aegilops'' species occupy most of the basal branch points in bread wheat evolution indicating that genus ''Triticum'' evolved from ''Aegilops'' after an estimated 4 million years ago. The divergence of the genomes is followed by allotetraploidization of a speltoid goatgrass x basal wheat species ''Triticum boeoticum'' with strains in the middle eastern region giving rise to cultivated emmer wheat.

Hexaploidization 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. This site, Ohala II (Israel), also shows that Triticeae grains were processed and cooked. Many cultivars appear to have been domesticated in the region of the upper Fertile Crescent, Levant and central Anatolia. 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.

Pastoral grasses

Triticeae has a pastoral component that some contend goes back to the Neolithic period and is referred to as th
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 graze animals, particularly cattle. Rye grasses in the New World have been used selectively 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 oats carried similar potentials, recent studies indicate that most oat sensitivity is the result of contamination. Triticeae glutens studies are important in determining the links between gluten and gastrointestinal, allergic, and autoimmune diseases. 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. One recent publication even raises doubts about wheat's safety for anyone to eat. Overlapping properties with regard to food preparation have made these proteins much more useful as cereal cultivars, and a balanced perspective suggests a variable tolerance to Triticeae glutens reflects early childhood environment and genetic predisposition.

References

External links

Pubmed:Triticeae

Database of Edible Seed Plants


- An excellent resource for the ancestral genetics of Triticeae.







Triticeae germplasm

{{Taxonbar, from=Q148694

Pooideae
Cereals
Poaceae tribes
Taxa named by Carl Linnaeus