Reduction in organ–organ friction is critical for corolla elongation in morning glory

Abstract

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.

Leaf morphogenesis: The multifaceted roles of mechanics

“…For example, fop1 mutants of Arabidopsis (Takeda et al, 2013) and ''cup flower'' mutants of Japanese morning glory (Ipomoea nil [L.] Roth, syn. Pharbitis nil [L.] Choisy) (Shimoki et al, 2021) show a folded-petal phenotype (Figure 7A). The stunted growth and folding of petals are due not to altered growth potential but to mechanical buckling induced by frictional forces between the petal surface and the neighboring sepals during growth (Figure 7B).…”

Petal segmentation in CT images based on divide-and-conquer strategy

“…However, it is impossible to survey how petals order and develop in three-dimensional (3D) space because the flowers have been decomposed. Importantly, it is known that surface interactions between petals and other floral organs in highly packed floral bud stage can influence the final flower shape ( Shimoki et al., 2021 ). To understand the process of petal growth and interactions among floral organs in flower bud stage, we need precise information on 3D arrangements of petals without destruction.…”

“…In recent years, computed tomography (CT) has been used to obtain nondestructive morphological information about flowers ( Hsu et al., 2017 ; Shimoki et al., 2021 ). Figure 1 shows the Camellia japonica 3D volume data used in this study.…”