Reduction in organ-organ friction is critical for corolla elongation in morning glory.

In complex structures such as flowers, organ–organ interactions are critical for morphogenesis. The corolla plays a central role in attracting pollinators: thus, its proper development is important in nature, agriculture, and horticulture. Although the intraorgan mechanism of corolla development has been studied, the importance of organ–organ interactions during development remains unknown. Here, using corolla mutants of morning glory described approximately 200 years ago, we show that glandular secretory trichomes (GSTs) regulate floral organ interactions needed for corolla morphogenesis. Defects in GST development in perianth organs result in folding of the corolla tube, and release of mechanical stress by sepal removal restores corolla elongation. Computational modeling shows that the folding occurs because of buckling caused by mechanical stress from friction at the distal side of the corolla. Our results suggest a novel function of GSTs in regulating the physical interaction of floral organs for macroscopic morphogenesis of the corolla. Shimoki and Tsugawa et al. propose that the reduction in inter-organ friction is an important factor in shaping flower morphology in morning glory. Using corolla mutants, they show that defects in glandular secretory trichomes result in folding of the corolla tube and release of mechanical stress by sepal removal restores corolla elongation.