Targeting trichome traits in tomato
Epidermal hairs (trichomes) protect plants from pests, UV and drought and secrete high-value products, including important pharmaceuticals. The control of trichome development is therefore a target for agriculture and biotechnology. Much is known about the control of Arabidopsis trichomes, but these are unusual because they are unicellular and evolved independently to the multicellular trichomes founds in almost all other species.
We have used Antirrhinum (snapdragon) species to understand control of multicellular trichome development. A former EASTBIO student identified a repressor of trichomes that is responsible for differences in hair density between species, and we have since found three different genes needed for trichome formation. As expected, none are present in Arabidopsis, though we already know that one of them has a conserved role in tomato. The orthologous genes of crop species could be targeted to alter trichome density. As a first translational step to crops, this project will test the role of these genes in hair formation in tomato—a crop and genetic model in the same Asterid I clade as Antirrhinum with similar secretory trichomes.
Are trichome genes conserved between species? Testing this will involve i) phylogenetics to identify orthologous tomato genes--all are members of fairly large gene families so it is important to understand whether genes duplicated in tomato; ii) RNA expression studies (RNA-seq and in situ hybridisation) to confirm that candidate orthologues are expressed in the epidermis and iii) testing the roles of the genes in trichome development by mis-expressing them in transgenic tomato plants or reducing their activity with CRISPR-induced mutations.
Tomato plants with different trichome densities will then use used to address one of two questions, depending on the student’s interests. 1) How do trichome genes interact in a regulatory network? This would involve testing how altered expression of one gene affects the activity of the others and whether gene products interact physically. Classic trichome mutations would also be incorporated in this analysis. How trichomes are spaced is of particular interest, because all of the genes we have identified so far are expressed throughout the epidermis, suggesting trichome cells are specified by a post-translational mechanism. 2) Are there disadvantages of trichomes? Not all species are densely hairy, suggesting trichomes have disadvantages that trade-off against their protective roles—e.g., because they reduce photosynthesis. This is an important consideration for crop improvement. Plants with different hair densities 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 with the help of Alistair McCormick, an expert in physiology and measuring plant growth by image analysis.
The project will provide training in phylogenetics and bioinformatics (including RNAseq analysis), statistics, plant molecular genetics, tomato transformation (training provided by collaborators), plant physiology and automated image analysis of plant growth, in collaboration with computer scientists.
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.
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.
If you wish to apply for this project, please go to this link.