Understanding how wheat measures the days and the seasons
Alex Webb, Head of Circadian Signal Transduction Group
Plants measure the seasons to produce flowers at the right time of year
In January we really notice the change of the seasons. One of the remarkable events that occurs at this time of year is the appearance of the flowers of the first snowdrops. In a few weeks the daffodils will appear, followed by the bluebells as we move fully into spring. This yearly progression of predictable flowering tells us that the flowering plants can measure the seasons. To ensure that plants produce their flowers at the right time of year, plants measure the length of the day and changes in temperature. Measuring the length of the day (or night) is achieved by internal 24-hour circadian clocks present in every cell of every plant acting as chronometers. These circadian clocks are conceptually similar to the ones in our brains; they are set by the day and light cycle and regulate daily events in the plant, but the genes that make up the components of the clocks are different between mammals and plants. The Webb laboratory is investigating how the genes of the circadian clock work together to produce a functional timing mechanism and how circadian clock genes might be used to improve crop production, particularly wheat.
The timing of grain production in wheat is an important agricultural trait
Wheat is the major crop in the UK. British wheat breeders have achieved incredible yields from our wheat fields, increasing from about 2 tonnes per hectare at the end of World War II, to around 8 tonnes per hectare currently. One of the contributors to our high productivity is the development of two main varieties that allow doubling cropping through the year; winter wheat is planted in the autumn and produces flowers, and therefore grains for harvest, in the spring. Spring wheat is then planted in the spring but produces its flowers at the end of the summer, for harvest in late August/September.
One of the main differences between spring and winter wheat is in the mechanisms by which they measure the seasons. Winter wheat can measure that the days are getting longer in early spring and once it detects this lengthening of the day, the plant produces flowers that go on to form the grain. However, this daylength-measuring mechanism is broken in spring wheat, which means spring wheat does not flower during the long days of early summer, and instead produces flowers as an old age response towards the middle and end of summer to ensure it reproduces the species before the end of the annual cycle of this plant. How wheat measures daylength, and the reasons why spring and winter wheat behave differently, are not understood in depth, but we do know some of the genes involved. As the climate changes we will need to tailor the timing of flowering and grain production to match local environments because prolonged heat, or cold, can damage the grain and reduce yield. We are providing the biological insight that will help breeders optimise the timing of wheat crop production.
We have characterised the role of one of the genes that regulates the timing of wheat crop production
We have found that one of the important genes involved in regulating flowering in wheat is what is now known as EARLY FLOWERING 3. We have discovered this gene has two independent roles in wheat. Firstly, we have shown that it forms part of the 24-hour clock present in every cell. Secondly, EARLY FLOWERING 3 has a direct role in regulating the flowering time of wheat, demonstrated by our field and laboratory studies of plants carrying different variants of the EARLY FLOWERING 3 gene, independent from its role in the circadian clock. This is exciting because it means it is possible to breed new wheat varieties with different flowering time properties, important as the climate changes, without affecting the essential functions of the 24-hour circadian clock in control growth, photosynthesis and the way the plant responds to pests and environmental stresses.
We are now trying to understand better how the EARLY FLOWERING 3 gene functions in the plant, and therefore the processes of daily and seasonal timing. We are doing this through experiments with plants with altered copies of this and other genes that we predict might be involved in the circadian clock and regulation of the timing of flowering. We are also making mathematical models that allow us to understand conceptuality how EARLY FLOWERING 3 and other genes work together to regulate the daily and seasonal events in wheat. The mathematical model will help describe the basic biology of the system, making it easier for breeders to select the gene varieties best suited for breeding for the specific trait they are interested in improving.
Cambridge is wonderful environment in which to perform this type of research. We have long experience of measuring the daily rhythms of plants, going back to Francis Darwin, son of Charles, who was interested in the daily plant movements. The Webb laboratory over the last 25 years developed specialised tools for measuring daily changes in physiology in the cells of wheat and other species, such as daily changes in leaf temperature caused by the opening and closing of stomata and activation and repression of genes. We are lucky also to be able to collaborate with Professor James Locke at the Sainsbury Laboratory Cambridge University, located at the Botanic Gardens, who is a leading expert in making mathematical models of circadian clocks. Our partners at NIAB in North West Cambridge have world leading expertise in wheat genetics and performing farm scale field trials, which has allowed us to extend our work from the laboratory to the farmer’s field.