Why plants can be great models for studying genetics

Gregor Mendel studied the inheritance of a number of pea traits including seed colour (yellow or green) and seed shape (smooth or wrinkled).

In 1866, a paper on the inheritance of traits in pea plants was published. The author was Gregor Mendel, a monk living in Brno (now in the Czech Republic). In the paper Mendel described how traits such as pea seed colour (yellow or green) and seed shape (smooth or wrinkled) were inherited and by doing so he built the foundations for modern genetics. Unfortunately, the paper stimulated little interest and Mendel died in 1884 with his scientific work largely unknown. It wasn’t until the early 1900’s that his work was rediscovered and more fully appreciated. It was supported by a number of prominent scientists of the time including William Bateson (the first director of the John Innes Horticultural Institution), who coined the term “genetics”.

Mesorhizobium loti: a bacterium with many friends

Mesorhizobium loti growing on TY agar. Can form a nitrogen-fixing symbiosis with the legume Lotus japonicus. Kazamia and colleagues (2012) found that it can also form a symbiotic interaction with the algae providing vitamin B12 in exchange for carbon. Image credit: Photograph by Ninjatacoshell distributed under a CC BY-SA 3.0 licence.

Last week I attended a PhD student symposium. It was a very interesting day filled with student research talks and poster sessions and networking. One of the talks was given by Matt Cooper (Alison Smith’s group University of Cambridge) about algal requirements for vitamin B12 and how these can be met by symbiotic (mutually beneficial) interactions with bacteria. One of the interactions mentioned was between the green alga Lobomonas rostrata and the gram negative bacteria Mesorhizobium loti.

I am familiar with M. loti as a nitrogen-fixing symbiont of the legume Lotus japonicus so I was surprised to hear it is able to provide vitamin B12 to algae. I resolved to find out more…

Medicago truncatula: a model legume

Medicago truncatula or barrel medic is native to the Mediterranean. It is a member of the legume family of flowering plants. More famous members of the family include pea, soybean, beans, peanuts and clover. It is grown as a forage crop (grown to be eaten by livestock) in Australia and has become a “model” species to study legumes. From a research perspective using  M. truncatula has the advantages that it is relatively small, has a short life cycle (3-4 months seed-to-seed) and can be transformed (have genes inserted into it). M. truncatula is the first legume to have its genome sequenced (1), providing a valuable tool for studying it and other legumes.

Medicago truncatula is a “creeper” so when we grow it in the lab we use stakes to enable us to fit more plants in a smaller space

The legume family is able to form a symbiosis, a mutually beneficial relationship with soil-living bacteria called rhizobia. The rhizobia are able to fix nitrogen gas from the atmosphere into ammonia, a form of nitrogen that plants can take up and use. Nitrogen is an essential plant nutrient and is in relatively short supply in the soil giving legumes an advantage over their non-legume competitors. In return for gaining a source of nitrogen the legume develops special organs on its roots called to house the rhizobia, providing sugars and a low oxygen environment to maximise nitrogen fixation.