Dr Stuart Casson

Commencing in August 2013

Career History

Research Interests

My laboratory is interested in understanding the mechanisms that regulate plant development and in particular, how environmental signals regulate core developmental pathways. For this purpose I am using stomatal development as a model. Stomata are microscopic pores on the surface of leaves that regulate gas exchange between the plants and their environment, allowing the uptake of carbon dioxide for photosynthesis whilst restricting water loss. This ability to control their gas exchange has allowed plants to colonise a number of environments and was arguably a crucial evolutionary step in the colonization of the land by higher plants.

Stomata can regulate plant gas exchange through short term changes in stomatal aperture. However, my research is focused on a longer term mechanism whereby plants adapt to changes in their environment by regulating their stomatal development, resulting in new leaves with altered stomatal numbers. Light and CO2 are particularly important in regulating these changes in stomatal development and we are beginning to identify the key components that regulate stomatal development in response to these signals. Understanding how these environmental signals interact to regulate stomatal development is vital if we are to accurately model plant water use and performance in a changing environment

Figure 1.
The epidermis of a developing leaf of the model plant Arabidopsis thaliana. Mature stomata (starred) consist of a pair of guard cells and arise from a series of stereotypical cell divisions.

Figure 2 (adapted from [4])
The key stages in stomatal differentiation are regulated by three closely related transcription factors; SPEECHLESS, MUTE and FAMA. SPCH has been shown to be targeted by a MAP kinase signaling cascade, although there is evidence that this MAPK pathway can act at each stage of stomatal development and is not always inhibitory. A set of membrane bound receptors act upstream of this MAPK pathway and the receptors bind a series of EPIDERMAL PATTERNING FACTORS, which are small peptides. Some of these EPFs, such as EPF1 and EPF2, negatively regulate stomatal development whilst STOMAGEN acts as a positive regulator. A protease, SDD1, negatively regulates stomatal development although its target has yet to be identified.

Figure 3 (from [4])
Environmental control of stomatal development. Light quantity and CO2 regulate epidermal cell fates leading to either an increase (light) or decrease (CO2) in stomatal numbers. The HIGH CARBON DIOXIDE (HIC) gene regulates stomatal development in response to CO2, whilst the red light photoreceptor phytochrome B and the transcription factor PIF4, regulate stomatal development in response to light signals.

Publications

1. Casson SA, Hetherington AM (2012) GSK3-like kinases integrate brassinosteroid signaling and stomatal development. Sci. Signal. 5, pe30 .

2. Ruszala EM, Beerling DJ, Franks PJ, Chater C, Casson SA, Gray JE, Hetherington AM (2011) Land plants acquired active stomatal control early in their evolutionary history. Curr Biol. 21: 1030-1035.

3. Barcala M, García A, Cabrera J, Casson S, Lindsey K, Favery B, García-Casado G, Solano R, Fenoll C, Escobar C (2010) Early transcriptomic events in microdissected Arabidopsis nematode-induced giant cells. Plant J. 61: 698-712.

4. Casson SA, Hetherington AM (2010) Environmental regulation of stomatal development. Curr. Op. Plant. Biol. 13: 90-95.

5. Portillo M, Lindsey K, Casson S, García-Casado G, Solano R, Fenoll C, Escobar C. (2009) Isolation of RNA from laser-capture-microdissected giant cells at early differentiation stages suitable for differential transcriptome analysis. Mol. Plant Pathol. 10: 523-535.

6. Casson SA, Franklin KA, Gray JE, Grierson CS, Whitelam GC, Hetherington AM. (2009) phytochrome B and PIF4 regulate stomatal development in response to light quantity. Curr Biol. 19: 229-234.

7. Casson SA, Topping JF, Lindsey K. (2009) MERISTEM-DEFECTIVE, an RS domain protein, is required for the correct meristem patterning and function in Arabidopsis. Plant J. 57: 857-869.

8. Gray JE, Casson S, Hunt L (2008) Intercellular Peptide Signals Regulate Plant Meristematic Cell Fate Decisions. Sci. Signal. 1: pe53.

9. Casson S, Gray JE. (2008) The Influence of Environmental Factors on Stomatal Development. New Phytologist. 178: 9-23.

10. Spencer MW, Casson SA, Lindsey K. (2007) Transcriptional profiling of the Arabidopsis embryo. Plant Physiol.143: 924-940.

11. Chilley PM, Casson SA, Tarkowski P, Hawkins N, Wang KL, Hussey PJ, Beale M, Ecker JR, Sandberg GK, Lindsey K. (2006) The POLARIS peptide of Arabidopsis regulates auxin transport and root growth via effects on ethylene signaling. Plant Cell 11: 3058-3072.

12. Casson SA, Lindsey K. (2006) The turnip mutant of Arabidopsis reveals that LEC1 expression mediates the effects of auxin and sugars to promote embryonic cell identity. Plant Physiol. 142: 526-541.

13. Casson S, Spencer M, Walker K, Lindsey K. (2005) Laser capture microdissection for the analysis of gene expression during embryogenesis of Arabidopsis. Plant J. 42: 111-123.

14. Mur LAJ, Xu RL, Casson SA, Stoddart WM, Routledge APM, Draper J. (2004) Characterization of a proteinase inhibitor from Brachypodium distachyon suggests the conservation of defence signalling pathways between dicotyledonous plants and grasses. Molecular Plant Pathology 5: 267-280.

15. Dean G, Casson S, Lindsey K. (2004) KNAT6 gene of Arabidopsis is expressed in roots and is required for correct lateral root formation.
Plant Mol Biol. 54: 71-84.

16. Casson SA, Lindsey K. (2003) Tansley Review: Genes and signalling in root development. New Phytologist 158: 11-38.

17. Casson SA, Chilley PM, Topping JF, Evans IM, Souter MA, Lindsey K. (2002) The POLARIS gene of Arabidopsis encodes a predicted peptide required for correct root growth and leaf vascular patterning. Plant Cell 14: 1705-21.