Epidermal hairs (trichomes) protect plants from herbivores, UV light or desiccation and are important sources of high-values compounds including pharmaceuticals and flavours. Increasing trichome density might improve resistance of crops or product yields. However, we know very little about the mechanisms that control development of multicellular trichomes – the type found in most species -- except that they are not shared with Arabidopsis. Therefore we do not yet have the tools to change trichome density. We also do not understand the potential downsides of increasing hairiness.
We have addressed this knowledge gap using snapdragons (Antirrhinum) as a model. We identified the Hairy gene that represses trichome formation in some species, making them bald. Hairy encodes a glutaredoxin that modifies TGA and HD-Zip transcription factor proteins, which we propose promote trichome formation. We have identified a fourth gene, Bald, which is needed for trichome production and inactive in some bald species.
The project aims to 1) confirm the role of the TGA and HD-Zip genes by using virus-induced gene silencing to reduce their expression in Antirrhinum, 2) identify Bald, by a combination of genome resequencing and transcriptomics, 3) further investigate the roles and interactions of these four genes, using molecular genetic approaches. This will provide understanding and a toolkit to attempt changing trichome density in a crop model.
Tomato, which has similar types of multicellular trichomes to Antirrhinum, will be used to test whether control of trichome development is conserved. Orthologues of the TGA and HD-Zip genes are found in tomato, so the function of these genes and of the Bald orthologue will be tested by changing their expression in transgenic tomato plants.
Hairiness in Antirrhinum can evolve by a single mutation yet many species remain bald, implying that trichomes can be a disadvantage in some conditions. Knowing the relative advantages and disadvantages is important when considering crop improvement. This will be examined in two ways. 1) We have created isogenic Antirrhinum lines that differ only in being bald or hairy. They will be compared for performance under different environments (temperature, humidity, light), for resistance to herbivores (aphids, caterpillars or snails), desiccation and UV light and for photosynthetic efficiency. 2) A large Antirrhinum hybrid zone in SE Spain contains both bald and hairy plants (reflecting inheritance of Hairy alleles). Geographic information system (GIS) analysis will be used to test association between environmental factors and hairiness across the region to find the conditions under which hairiness or baldness are favoured.
The project will provide training in areas spanning molecular genetics, plant transformation, bioinformatics (genomics transcriptomics and phyllogenetics), animal-plant interactions, field work, plant physiology and GIS.