Who do you think you are? Modern Bread Wheat edition

Who do you think you are_ Modern bread wheat edition

Wheat, what would I do without you. I wouldn’t have been able to eat my tasty bread roll for lunch, my breakfast would have been lacking – I don’t even want to think of what I would have eaten for 70% of my teatime meals at university (although of course pasta isn’t made bread wheat). Yes, wheat is an important staple of many of our diets today. I am sure every time you tuck into garlic bread, your first thought is “well how did this wheat come about?”. No? Of course garlic bread is too delicious to think about anything else I suppose. I am introducing to you the domestication series, where I tell you everything you could ever want to know about how agricultural crops have came to where they are today.

Geographically, wheat originated in the Fertile Crescent, with estimations of bread wheat being first cultivated from 10,000 years before present. I haven’t particularly got on very well with history before, but to me that sounds pretty ancient.

Fertile Crescent 2
The Fertile Crescent

 

 

Where does wheat sit in the grand scheme of the plant kingdom? Wheat is a member of the grass family (Poaceae for the botanically minded of you out there), it also belongs to the tribe (just a further classification of living things) Triticeae.

 

Poaceae family
Families in the Plant kingdom. Wheat is in the grass family, known as Poaceae.

 

Now, modern bread wheat didn’t just turn up one day, there are many species that have contributed to the evolution of modern bread wheat. Polyploidy – a term used to describe how many copies of a gene an organism has – is massively important in the evolution of wheat. Wait, what is polyploidy? So humans are known as diploid because we have two copies of each gene in our genome, one copy inherited from each parent. Genome is a word used to describe the genetic make-up of organism, all the genes that make an organism, usually organised into structures called chromosomes. Some of the species that were involved in the evolution of modern bread wheat are also diploid, however some are tetraploid, these contain four copies of each gene and others are hexaploid which contain six copies of each gene. The different copies of the gene belong to different sets of genomes, these are referred to as A, B and D genomes when talking about the evolution of wheat. So there will be two copies of the genes in the A genome, two copies of the genes in the B genome and two copies of the genes in the D genome. Your sandwich just got a whole more complicated right?

Human and wheat karyotypes
The genetic makeup of humans (left), which is organised into 22 pairs of chromosomes (+sex chromosomes). The genetic makeup of Modern Bread Wheat (right) (of the variety “Cappelle-Desprez”), which is organised into three genomes A, B and D which each contain 7 pairs of chromosomes.

Let’s begin. Step one in the evolution of modern bread wheat is the evolution of Einkorn wheat. Einkorn wheat is an ancient wheat which was cultivated until the bronze age. Initially this started with ancient wild Einkorn (also known Triticum boeoticum) which then evolved into Einkorn wheat (known as Triticum monococcum). The arrows shown in all the diagrams represent a series of changes, caused by changes in the genes and genetic makeup of the wheat which has led to a different species being formed.

Einkorn domestication(3)
Initial domestication of einkorn wheat

In another set of events, another member of the Triticum genus (Triticum uratu) , with a further evolved A genome has hybridised (bred) with an unknown species, which has a B genome. This forms tetraploid wheats, with AB genomes: emmer and durum (pasta – yay!).

Step 2 wheat domestication
Hybridisation of A and B genomes

Emmer wheat and durum wheat somehow combined/bred together with a species that is a “goatgrass”. The ABD genome was then born, to form two hexaploid wheats: spelt (Triticum spelta) and modern bread wheat (Triticum aestivum).

Step 3 wheat domestication
Hybridisation of A and B genomes with D genome to form spelt wheat and modern bread wheat

You may notice the names of some of the other forms of wheat: emmer, spelt or einkorn. Many researchers are looking at these as a source of diversity to enhance the characteristics of modern bread wheat by breeding – I can talk about this in another post. Some hipster-folks and others are also looking at these ancient wheats to incorporate them into our food today.

Hope this post was semi-intersting, if you want to know more or I explained something badly let me know on twitter (@alicefoxall) or comment and I’ll get back to you. Also let me know if there are any more crops you would love to hear about.

I am using information from the things that I remember from university, but of course I can provide references if you so wish 🙂

 

 

 

 

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