Epigenetic regulation of seed size in Arabidopsis: harnessing ecotype variation in paternal killer genes
Student: Catherine Wilkins
Supervisors: Dr James Doughty (Department of Biology and Biochemistry, University of Bath), Prof Rod Scott (Department of Biology and Biochemistry, University of Bath)
Many plants, including agronomically important species, exhibit post-zygotic barriers to hybridization, in both interploidy crosses within a species and interspecific crosses between related species, even at the same ploidy levels. These barriers prevent production of potentially valuable new hybrids, but importantly also provide opportunities to manipulate seed size and potentially seed yield in crop plants. This is important in helping to address food security issues that continue to intensify due to population growth.
Genetic variation exists in the operation of the post-zygotic hybridization barrier in Arabidopsis thaliana. Most Arabidopsis ecotypes (land-races) tolerate reciprocal diploid by tetraploid hybridizations (2xX4x and 4xX2x) to produce viable large and small seeds respectively that contain triploid embryos. However, a small number of ectotypes, including Columbia (Col) (Dilkes et al PlosB, 2008), tolerate 4xX2x crosses but are acutely sensitive to paternal excess 2xX4x crosses, with most of the resulting seed dying due to severe over-proliferation of endosperm tissue (seeds try to get too large and fail). Thus the Col ecotype operates an asymmetric hybridization barrier, where paternal excess causes lethality but maternal excess does not. This Col-killer effect is associated with 2x sperm produced by tetraploid plants, is independent of the mechanism leading to chromosome doubling, and is under epigenetic control. Gaining a mechanistic understanding of the Col-killer effect will provide us with important information on how seed size is regulated and opens up exciting opportunities for the biotechnological improvement of seed yield in crop plants.
This project will
i) utilize tetraploid recombinant inbred lines developed at Bath to map and identify the Col-killer genes,
ii) through molecular genetic approaches decipher the mode of action of the candidate gene(s) in diploid and tetraploid parents,
iii) establish the epigenetic status of the Col-killer genes in diploid and tetraploid lines as well as non-‘killer’ ecotypes,
iv) develop strategies to deploy these genes for crop improvement.
Pesticide “hang-overs” and social disruption in pollinator societies
Student: Sam Duckerin
Supervisors: Dr Seirian Sumner (School of Biological Sciences, University of Bristol), Dr. Heather Whitney (School of Biological Sciences, University of Bristol) and Dr. Richard James (Department of Physics and Centre for Networks and Collective Behaviour, University of Bath).
Insect pollinators are essential for our food security. The recent global declines of key pollinators are therefore of great concern for global food production. The social bees are one of the most important crop pollinators, with their services valued at over $200billion per year. One major concern is whether pesticide use is responsible for the observed declines in pollinator populations. Recent research has shown that pesticides affect physiology and brain function of individual bees, and that pesticide exposure may be detrimental to foraging efficiency of workers and brood productivity. Yet, we lack essential mechanistic understanding of how pesticides disrupt insect behaviour, from genes to phenotype.
This studentship will explore how pesticides disrupt social behaviours and colony-level interaction networks in pollinator societies, and whether such social disruption leads to suboptimal colony performance. Exposure to pesticides may impair the ability of individuals to interact, communicate and cooperate with their colony mates. There may be transient effects of individual-level exposure on colony function which ‘end-point’ studies miss. For example, what colony-level impact does a pesticide ‘hang-over’ have, where individuals may be affected for only a short time period after exposure? Finally, we know nothing about the genes associated with changes in behavior after pesticide exposure.
Do agri-environment schemes enhance biodiversity under the challenge of agricultural intensification?
Student: Jeremy Froidevaux
Supervisors: Professor Gareth Jones (School of Biological Sciences, University of Bristol) and Professor Richard Wall (School of Biological Sciences, University of Bristol).
While increases in crop yield and agricultural system productivity are essential to maintain food security it is vital that biodiversity is also conserved. Agricultural landscapes are especially important for biodiversity as they comprise three-quarters of the UK’s land area (Defra 2008). However, agricultural intensification has contributed to biodiversity declines in a wide range of taxa over the past 50 years (Krebs et al. 1999: Nature 400: 611-612; Robinson & Sutherland 2002: Journal of Applied Ecology 39: 157–176).
Agri-environment schemes can potentially reverse negative impacts of agricultural intensification. Defra operates Environmental Stewardship schemes in which landowners are paid to enhance habitats in areas where threatened species occur. Evidence for whether these schemes are successful is lacking. Indeed recent studies suggested that although moth abundance was higher on farms involved in agri-environment schemes specific to Scotland, the activity of pipistrelle bats was higher on conventionally-managed farms (Fuentes-Montemayor et al. 2011a,b: Biological Conservation 144: 2233-2246; Journal of Applied Ecology 48: 532–542). These schemes appear, therefore to have complex impacts on ecosystem community structure.
Here we will compare the diversity, activity and abundance of key indicator organisms in agricultural landscapes under Environmental Stewardship compared with matched sites not under stewardship.
For this we will use bats and their invertebrate prey as bioindicators. The activity and species richness of bats and their insect prey (Wickramasinghe, Jones et al. 2003; 2004: Journal of Applied Ecology 40: 984-993; Conservation Biology 18: 1283-1292) are higher on organic farms compared with matched conventional counterparts. Organic farms retain many features typical of farms before agricultural intensification, suggesting that intensification had a detrimental effect on bats and their insect prey.
How does circadian regulation increase water use efficiency?
Student: Noriane Simon
Supervisors: Dr Antony Dodd (School of Biological Sciences, University of Bristol) and Professor Alistair Hetherington (School of Biological Sciences, University of Bristol).
Circadian regulation in plants increases photosynthesis and water use efficiency (WUE) (Dodd et al. Science 2005). The mechanisms underlying the circadian optimization of WUE are unknown. We will address this question, using Arabidopsis-based underpinning research. This question is important for future food security, because a research priority is to develop productive crops that use less water (Royal Society, 2009). The student will:
1. Produce a toolkit of transgenic plants with misregulated guard cell circadian oscillators. Guard cell-specificity will be achieved with the guard cell-specific promoter MYB60 and GAL4-GFP enhancer trap lines. AD has produced a preliminary toolkit with arrhythmic guard cells.
2. Position circadian oscillator components within the daily regulation of stomatal aperture and identify oscillator components that optimize WUE. Circadian regulation of stomatal opening, transpiration and photosynthesis will be investigated using the toolkit described. Experiments will determine whether specific oscillator components contribute to WUE at specific times of day or under certain abiotic stresses.
3. Using their data, the student will use linear time invariant (LTI) models to approximate the control relationship between oscillator components and WUE alterations over circadian and diel cycles. LTI models are ideal for mapping system inputs to system outputs where network topology and biochemical rate constants are unknown (as is the case for circadian control of stomata) (Dalchau et al. 2012).
4. Use LTI model predictions to form hypotheses concerning oscillator states that determine specific WUE outcomes. These will be tested with experimental manipulations to oscillator and environment.