A comparison of early floral ontogeny in wild-type and floral homeotic mutant phenotypes of Primula

Abstract

Primula flowers are heteromorphic with individual plants producing either pin-form or thrum-form flowers. We have used scanning electron microscopy to observe early development of wild-type flowers of primrose (Primula vulgaris), cowslip (P. veris), and the polyanthus hybrid (P. · tommasinii · P. vulgaris). Floral ontogeny in Primula is different from that observed in the well-studied models Antirrhinum majus and Arabidopsis thaliana and our studies reveal morphological landmark events that define the sequence of early floral development in Primula into specific stages. Pinform and thrum-form flowers are indistinguishable during early development with differentiation of the two floral morphs occurring beyond the differentiation of floral organs. Early ontogeny of flowers with homeotic mutant phenotypes was also studied to determine the timing of developmental reprogramming in these mutants. Phenotypes studied included Hose in Hose and Jack in the Green that develop petaloid sepals and leafy sepals, respectively, and Jackanapes plants that carry both these dominant mutations. Recessive double and semi-double flowers that produce additional whorls of petals and/or stamens in place of carpels were also studied. We describe a previously undocumented recessive Primula mutant phenotype, sepaloid, that produces sepals in place of petals and stamens, and a new nonhomeotic, dominant mutant phenotype Split Perianth, in which sepals and petals fail to fuse to form the typical calyx and corolla structures. The molecular basis of these mutant phenotypes in relation to the ABC model is discussed.

A new day dawning: Hemerocallis (daylily) as a future model organism

“…Even the basic histology and developmental biology are yet to be investigated. Such studies would complement recent work on dicots, chiefly Primula (primrose) cultivars with aberrant floral development (Webster and Gilmartin 2003; Li et al 2008, 2010).

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Oakleaf: an S locus‐linked mutation of Primula vulgaris that affects leaf and flower development

“…In order to explore the influence of Oakleaf on leaf and petal development and to examine whether the effects are organ-specific or whorl-specific, we combined Oakleaf with the following mutant phenotypes: Hose in Hose (Webster & Grant, 1990;Li et al, 2010), a dominant mutant phenotype in which sepals are converted to petals; Jack in the Green (Webster & Gilmartin, 2003), a dominant mutant phenotype in which sepals undergo a homeotic transformation to leaves; and Jackanapes (Webster & Gilmartin, 2003), a double mutant carrying both Jack in the Green and Hose in Hose dominant alleles, which produces hybrid petal/leaf structures in the first floral whorl.…”

“…Plants were grown as described previously (Webster & Gilmartin, 2006). Hose in Hose, Jack in the Green and Jackanapes (Webster & Grant, 1990;Webster & Gilmartin, 2003) were crossed with Oakleaf, and controlled crosses between Oakleaf and wild-type were performed, in insect-free environments following emasculation of pollen recipients by removal of corolla and anthers. Seed was harvested from ripe seed capsules and stored at c. 4°C in air-tight containers.…”

“…Floral apical meristems and developing buds were dissected using scalpels and razor blades with a 920 hand lens. Samples were prepared for cryo-SEM, analysed and images recorded as described previously (Webster & Gilmartin, 2003).…”

“…Several genes linked to the S locus in P. sinensis and P. vulgaris, but not directly involved in floral heteromorphy, have been identified through analysis of mutants and phenotypic variation, including flower pigment genes (Gregory et al, 1923;De Winton & Haldane, 1933, 1935Kurian, 1996), Hose in Hose (Ernst, 1942;Webster & Grant, 1990;Webster & Gilmartin, 2003;Webster, 2005) and sepaloid (Webster & Gilmartin, 2003;Webster, 2005;Li et al, 2008). Related studies on differential gene expression also identified genes that are differentially regulated in response to the S locus (McCubbin et al, 2006), and genes and polymorphisms located at, or close to, the S locus (Manfield et al, 2005;Li et al, 2007).…”