Abstract
Flowers are vital for attracting pollinators to plants and in horticulture for humans. Petal morphogenesis is a central process of floral development. Petal development can be divided into three main processes: the establishment of organ identity in a concentric pattern, primordia initiation at fixed positions within a whorl, and morphogenesis, which includes petal elongation through the narrow spaces within the bud. Here, we show that the FOLDED PETALS 2 (FOP2) gene, encoding a member of the half-size ATP binding cassette (ABC) transporter family ABCG13, is involved in straight elongation of petals in Arabidopsis thaliana. In fop2 mutants, flowers open with folded petals, instead of straight-elongated ones found in the wild type. The epicuticular nanoridge structures are absent in many abaxial epidermal cells of fop2 petals, and surgical or genetic generation of space in young fop2 buds restores the straight elongation of petals, suggesting that the physical contact of sepals and petals causes the petal folding. Similar petal folding has been reported in the fop1 mutant, and the petals of fop2 fop1 double mutants resemble those of both the fop1 and fop2 single mutants, although the epidermal structure and permeability of the petal surface is more affected in fop2. Our results suggest that synthesis and transport of cutin or wax in growing petals play an important role for their smooth elongation through the narrow spaces of floral buds.
Highlights
Petals have evolved to have various colors, shapes, and fragrances, and, their morphogenesis is critical in attracting pollinators for plants and in horticulture for humans
During a screen for floral organ defective mutants in Arabidopsis thaliana, we found a couple of mutants defective in the petal elongation process
Their flowers open with folded petals instead of wild-type straight-elongated ones, so we named these mutants folded petals
Summary
Petals have evolved to have various colors, shapes, and fragrances, and, their morphogenesis is critical in attracting pollinators for plants and in horticulture for humans. First is the identity determination, described by the floral ABCE model, which explains that the organ identity is established in a concentric pattern by combined functions of the floral homeotic genes [1,2,3,4] In addition to these main factors, miRNA172 and other transcription factors such as AINTEGUMENTA, LEUNIG, SEUSS, RABBIT EARS (RBE), and STERILE APETALA, are involved in fine-tuning of expression of the floral ABCE genes in Arabidopsis thaliana [5,6,7,8,9,10,11,12,13]. Is expressed in growing petals, suggesting that FOP1 is involved in production of fatty acids that makes petal elongation smooth in narrow space in floral buds, and that petal morphogenesis is affected by the physical interaction of floral organs. Our results suggest that FOP2 regulates petal elongation at distinct stages of the same pathway of FOP1, and that export of cutin and/or wax to the surface of the petal epidermis is important for petal morphogenesis
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