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Plant Day 2012

Our last post looked forward with heightened anticipation to Wild about Plants, Sheffield Uni’s contribution to Fascination of Plants Day 2012.  This was a festival of plant sciences, developed in partnership with science clubs at two local secondary schools, and run on the day for three local primary schools. The day was a great success: everything went to plan, the activities worked out, and the primary school kids had a lot of fun. But most impressive was how the Y9s from King Edwards and King Ecgberts Secondary Schools took charge on the day, running each activity with a fantastic level of confidence and expertise. What stars!

So, a big thanks to all the schools that took part, to our university ambassadors for their hard work in developing the activities, the university Outreach department for their support, and Science Brainwaves, especially Dominic Swain, for helping to put it all together. Here’s the story of the day in photos ….

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Wild about Plants

Friday 18th May is the first international “Fascination of Plants Day”, and Sheffield Uni are joining this jamboree with a festival of plant science for school kids. Our teams of researchers and students have developed Wild about Plants in partnership with Y9 after-school clubs at King Edwards and King Ecgberts secondary schools in Sheffield. The emphasis has been on having a bit of fun, whilst demonstrating some cool things that plants do: focusing on photosynthesis, transpiration, pollination and defence. We’ve put together a diverse range of hands-on activities for the event, and on the day will run these for Y5s visiting from Westways primary school in Sheffield, and St Dominics and Holy Cross primary schools in Barnsley. Other activities on the day include a “match the product to the plant” treasure hunt, a “design and make your own seed” workshop, and a Project Sunshine photovoltaic verses photosynthesis show-down. We’re excited about the day ahead of us, and looking forward to having fun with our visitors. Photos of the day will appear on Colin’s twitter feed (@sheffieldplants) and in a future post. Watch this space …

Lateral transmission of genes for C4 photosynthesis

The origin of complex traits, such as eyes and wings, has been studied by biologists since Darwin. In all cases looked-at so far, new traits have arisen through the modification of genes inherited from ancestors, and we’ve long understood how these evolutionary adaptations are passed from parents to offspring. But in a new paper published this month in Current Biology, we’ve discovered an exception to this rule, showing that adaptive genes required for a complex trait can be transmitted between distant plant cousins without direct contact between the species.

We looked at the evolution of genes involved in the C4 photosynthetic pathway, a well-studied complex trait that boosts productivity in hot environments. Our study organism was Alloteropsis semialata, an African grass that’s a favourite of ours for work on C4 evolution and ecology. For the first time, our work has revealed that crucial elements of this pathway have been transmitted between distantly related grass species. This unexpected discovery of adaptation by “lateral gene transfer” adds to growing evidence that the evolutionary tree of life is better described as a tangled bush. Crucially, it shows that genetic adaptations can cross the species boundary and spread among unrelated plants.

Lateral gene transfer. Credit: Les Watson and Wikipedia Commons

Lateral gene transfer among grass species: photo credits Les Watson and Wikipedia Commons.

Dr Hui Liu!

Congratulations to lab member Hui Liu who successfully defended her PhD thesis today. The celebrations have begun….

Hui’s thesis examined phylogenetic patterns in the ecology, morphology and physiology of grasses. Look out for papers on these topics from Hui in the coming months. The first is due out in Oecologia.

New hypothesis on C4 evolution

Colin has published a new hypothesis about the evolution of C4 photosynthesis in a paper with Lawren Sack from UCLA appearing in this month’s Philosophical Transactions of The Royal Society. In it, we argue that plant hydraulics should be considered an important aspect of C4 plant evolution (link to paper).  An interaction with CO2 arises because atmospheric CO2 starvation forces plants to open stomata wider, causing greater loss of water.  C4 plants reduce this problem with a CO2-concentrating mechanism that boosts photosynthesis without the need for high water loss. The paper was reported today by the online magazine Planet Earth: read more here. The paper is part of a theme issue of Phil. Trans. B looking at the roles played by atmospheric CO2 in plant evolution (link to journal).

PEPG mini-symposium

Several members of the group attended the first annual BES Plant Environmental Physiology Group mini-symposium in London. After a long day of interesting talks at Charles Darwin House, the discussion continued in a local pub.

Expedition to Madagascar

Russell Hall just got back from a plant collecting expedition to Madagascar to seek out grasses in the Forest Shade Clade – a group of around 150 species, including both C3 and C4 lineages. The main goal was to collect fresh material for DNA extraction, as part of the effort to construct a densely sampled phylogeny of the Forest Shade Clade of grasses. The phylogeny will be used to explore the history and causes of photosynthesis evolution in this clade using comparative methods.

Madagascar was targeted for collection as a third of the species in the clade grow in Madagascar, and a fifth of them are endemic to Madagascar.

A brief account of the expedition is given on the eMonocot project website.

Evolution: there and back again?

The C4 pathway is a turbo-charger for photosynthesis that has evolved from the ancestral C3 type of photosynthesis many times in nature. But just how many times remains an open question. This is important because scientists are currently working hard to bioengineer highly productive C4 rice crops in the laboratory. Learning that the pathway is easy to evolve would bring great hope to this enterprise.

Origins of the C4 pathway are inferred by looking at its distribution across the evolutionary tree of life. Purely C4 lineages interspersed by C3 lineages can be interpreted as independent evolutionary origins of the pathway. However, evolutionary theory tells us that a complex trait like C4 photosynthesis should be easier to lose than it is to acquire. If this is true, it would mean the pathway could actually have evolved very few times, way back in time, with many lineages subsequently reverting back to the ancestral C3 type of photosynthesis.

We tackle this problem in a paper published this month in Trends in Ecology and Evolution, arguing that assembly and deconstruction of the C4 pathway are equally difficult. There is no reason to expect evolutionary loss of C4 photosynthesis to be more common than evolutionary origins. Current genetic evidence backs this claim; reversal back to the C3 pathway seems to be extremely rare and may not even occur at all. However, the piecewise evolutionary assembly of C4 photosynthesis seems to involve a huge number of steps, and could well have been reversed many times before it was completed. In order to detect these reversals, we will need a much better understanding of the genetics underpinning the pathway.

Download the paper here

Grassland origins

The origin of C4 photosynthesis is the most important evolutionary innovation in plants since the evolution of flowers. It has dramatic effects on plant performance, and turbo-charges growth in hot sunny environments. Today, grasses using the C4 photosynthetic pathway dominate tropical savannas and warm-climate grasslands across large areas of the Earth’s surface. The geological record tells us this ecological dominance arose suddenly around 8-3 million years ago. Why?

For a long time, the C4 pathway itself has been considered a crucial part of the answer, the argument being that this new form of photosynthesis gave a performance advantage to the grasses that used it. In a new paper published in Science, we suggest that the drivers of C4 grassland expansion were significantly more complex. It is time to start looking beyond the C4 pathway to other traits that could allow species to dominate grassland ecosystems.

In our paper, we propose a new way forward, in which grass evolutionary biology is synthesized with grassland ecosystem science. We think this will help to increase our knowledge of the evolution of plant traits that promote dominance in grassland systems, and better our understanding of the key question: just how important was C4 photosynthesis in transforming ecosystems across large regions of the Earth’s surface?

Download the paper here

Efficiency savings

At high temperatures, the C4 pathway greatly increases the efficiency of photosynthesis over the C3 type. This means that C4 leaves can use less water and nitrogen than their C3 counterparts, without cost to photosynthesis. That’s the theory at least and, until now, it’s been backed by experimental data.

We challenge this view in a new paper, which reports an experimental comparison of more than 30 grass species from closely related C3 and C4 groups. We find no evidence of a C3 / C4 difference in nitrogen content. This result raises the intriguing possibility that evolutionary history may be more critical for plant nitrogen usage than photosynthetic pathway. But what about water? Just as expected, the C4 species used less than their C3 relatives, providing significant improvements in plant water status.

Download the paper here