The InMYB1 promoter from Japanese morning glory is active specifically in petals of various dicotyledonous plants. To determine whether this promoter functions by recognizing whorl position within the floral meristem or petal identity, Azuma et al. (on pp. 580-587) examined its activity in various mutant and transgenic Arabidopsis plants in which ABC model genes had been modified. They found that the InMYB1 promoter specifically recognizes petaloid cell identity, suggesting that this promoter can be used as a reliable cell type-specific marker in plants.