Mechanisms of proximo-distal polarity establishment and tissue patterning in Hibiscus petals

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PhD project strategic theme: Understanding the rules of life The colourful patterns on the petal of flowering plants are key to attracting pollinators and participate directly in the reproductive success of a species. These patterns are often highly elaborate and combine differences in pigmentation, cell shape and ornamentation of the cuticle so their development must be tightly regulated to generate neighbouring tissues with distinct properties. How such clear boundaries are established within the petal epidermis as it grows remains to be understood.The Moyroud group at the Sainsbury Laboratory (University of Cambridge) has developed a species of Hibiscus as a new model system to understand how those patterns form on petals. Using a transcriptomic approach, they identified genes whose expression is restricted to distinct parts of the petal in very early stages of development, before pattern formation. Those constitute candidate genes likely to act as upstream regulators of pattern formation.The proposed project will aim at (i) testing a new hypothesis regarding the nature of the signal that organises the petal base-to-tip polarity, (ii) exploring the interplay between cell polarity and tissue polarity in petals, and (iii) identifying the downstream gene regulatory network(s) responsible for pattern formation. To do so, a range of molecular biology techniques will be used in combination with state-of-the art genetic manipulations in an emerging model system (cloning, quantitative PCR, construction of overexpression and CRISPR/Cas9 knock-out Hibiscus lines, production of transgenic plants expressing fluorescent sensors for metabolites of interest and transcriptomics). This project will also involve external assays: candidate molecules will be applied to developing buds in planta or on isolated petals using a custom-made in vitro petal growth system to assess their ability to interfere with petal patterning. Finally, confocal, Raman and scanning electron microscopy methods will be used to analyse phenotypes of treated buds/petals, transgenic lines and mutants with defect in pattern formation recently identified in a genetic screen.