A CYCLOIDEA-like gene mutation in sunflower determines an unusual floret type able to produce filled achenes at the periphery of the pseudanthium

Abstract

The pseudanthium of sunflower (Helianthus annuus L.) consists of two floret types: zygomorphic sterile ray florets and\ud actinomorphic hermaphrodite disc florets. In the tubular ray flower (turf) mutant, the loss-of-function of a CYCLOIDEA (CYC) gene\ud generates hermaphrodite tubular-like ray florets that replace the normal sterile ray florets. We evaluated whether tubular-like\ud ray florets have a multifaceted set of floral traits and the presence of heteromorphic seeds in the turf inflorescence. During early\ud stages of floral ontogeny, primordia of both tubular-like ray florets and typical ray florets displayed a comparable shape. In\ud contrast, during later stages of development, the form of tubular-like ray floret primordia was most similar to disc floret\ud primordia. In mature tubular-like ray florets, corolla and ovary had both ray and disc floret characteristics but also displayed\ud distinct identity traits. In open-pollinated tubular-like ray florets, the seed set was low, but a noteworthy increase of filled\ud achenes was obtained by hand pollination. Wild type ray achenes were always empty. Embryos of tubular-like ray florets were\ud shorter and lighter than the embryos of disc florets but able to produce fertile plants. In conclusion, the different identity\ud characteristics combined in tubular-like ray florets of the mutant evolved a capitulum type not described in the genus Helianthus

Quantitative Classification of the Morphological Traits of Ray Florets in Large-flowered Chrysanthemum

“…There have been some reports of floral organ regulation in the Compositae. For example, some studies have shown that CYC-like genes play an important role in the symmetry of ray floret in members of the Compositae (Chapman et al, 2012;Juntheikki-Palovaara et al, 2014;Liu et al, 2016;Mizzotti et al, 2015). Ray floret architecture in chrysanthemum may range from a flat type (lateral symmetry) to tubular type (radial symmetry), and we found that there are many intermediate states between these extremes, suggesting that this is quantitative character.…”

Ligulate inflorescence of Helianthus × multiflorus, cv. Soleil d'Or, correlates with a mis‐regulation of a CYCLOIDEA gene characterised by insertion of a transposable element

“…The high number of anther/flower in ray‐like flowers might be a related to the origin of these flowers from hermaphrodite actinomorphic disc flowers (Mizzotti et al . ). The presence of anther and styles also in true ray flowers (Table , Fig.…”

“…; Mizzotti et al . ). In addition, the incomplete filaments attached at the base of the corolla tube of ray flowers of sunflower are likely a remnant of ancestral stamens.…”

“…Inside the anther tube is the style, terminating in a divided stigma with receptive surfaces in close contact in the bud stage before the flower opens (Mizzotti et al . ).…”

High-density genetic map construction and identification of loci controlling flower-type traits in Chrysanthemum (Chrysanthemum × morifolium Ramat.)

“…For example, some researchers have suggested that the petal type of Compositae species shows a change from bilateral asymmetry (flat type) to radial symmetry (tubular type). Therefore, researchers have focused on genes related to floral symmetry, such as the CYC-like gene 41,42 . However, our study suggests that many intermediate types exist between the flat and tubular types in chrysanthemum, which means that the variation in petal type (redefined in our study as CTMD) is partly determined by floral symmetry.…”