Petal colour intensity is an adaptation that flowering plants have made to lure pollinating insects. A conical-shaped petal epidermal cell has increased colour intensity because more incidental light is reflected into it. MIXTA, a MYB-related transcription factor, regulates conical cell shape development in snapdragon (Antirrhinum majus) petals. Cathie Martin and co-workers report that proteins closely related to MIXTA from both A. majus and other angiosperms have similar, but distinct, roles in petal epidermal cell shape formation (). Cell shape contributes to the overall petal curvature, and thus flower shape, a role not previously associated with MIXTA-like proteins. Using genetic mutants from snapdragon and petunia (Petunia hybrida),the authors reveal the occurrence of flatter epidermal cells in mixtamutants and of shallow, conically shaped cells in petunia phmyb1mutants. They propose that an altered direction of growth, followed by growth extension, generates cell shape in this setting. This family of transcription factors, in modifying the petal epidermal cell shape, fulfil a crucial role in attracting insects, thus ensuring pollination.
