Epidermal hairs (trichomes) protect plants from pests (and the diseases they carry), UV light and drought. Some also secrete high-value products, including important pharmaceuticals. Increasing hair coverage is therefore a potential target for both increasing natural resistance of crops in a sustainable way and for biotechnology. However, there are currently two obstacles to achieving this. 1) We know relative little about the networks that control hair development, which could be targeted to alter hair density. 2) We do not know whether increasing hair density will have undesirable side effects on plant performance.
Though control of hair development is well understood in Arabidopsis, its hairs are single celled and are not regulated in the same way as the multicellular hairs found in most other plants. We, and others, have identified genes that regulate multicellular hairs: specifying which epidermal cells will become hairs and then which hairs will form secretory glands. We have also developed a model to explain how these genes interact in a regulatory network. However, we have not been able to test this model fully because its components come from different species (e.g., snapdragon, tomato, cucumber).
The first phase of this project will involve genome-editing tomato plants to introduce mutations in hair-regulating genes known from other species and to examine how these affect tomato hairs. This will test the assumption that gene functions are conserved between species. The next step is to examine how the gene interact in a regulatory network (e.g., whether one gene promote or inhibits expression of another), to test whether interactions known in other species are also conserved and to discover new interactions. This information will be used to identify which genes may be altered to increase hair density with fewest side effects. Repressors of hair formation are key targets, because they would allow use of natural or genome edited loss-of-function mutations to increase hair density, rather than GM.
Tomato lines with different hair densities will be use used to test whether there disadvantages, as well as advantages of trichomes. Not all species are densely hairy, suggesting trichomes have penalties that trade-off against their protective roles—e.g., because they reduce photosynthesis. Plants will be compared for performance (growth rate and yield) in different environments (light intensity, humidity temperature etc) and the effects of hairs on photosynthesis and water loss examined in detail. These experiments will be done in collaboration with experts in physiology and measuring plant growth by image analysis within Edinburgh. There is a lot of evidence that trichomes protect against pests. However, the evidence for protection against drought or UV is less certain. We can test this by comparing water loss in bald and hairy plants and whether bald plants are more prone to being damaged by UV radiation.
The project will provide training in in plant molecular genetics, microscopy (light and scanning EM), bioinformatics (including RNAseq analysis), genome editing and plant transformation, plant physiology and automated imaging of plant growth (in collaboration with computer scientists).
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Tan Y, Barnbrook M, Wilson Y, Molnár A, Hudson A. Loss of a glutaredoxin gene underlies parallel evolution of multicellular trichome patterns in the genus Antirrhinum. http://biorxiv.org/cgi/content/short/518183v2.
Glas JJ et al., (2012). Plant glandular trichomes as targets for breeding or engineering of resistance to herbivores. doi: 10.3390/ijms131217077.
HuchelmannA, Boutry M, Hachez C (2017). Plant glandular trichomes: natural cell factories of high biotechnological interest. doi: https://doi.org/10.1104/pp.17.00727.
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