Molecular Mechanism Regulating Floral Architecture in Monocotyledonous Ornamental Plants

Abstract

Molecular and genetic analyses of flower development have been conducted primarily in dicot model plants such as Arabidopsis thaliana and Antirrhinum majus. The obtained data are the basis for the ABC model, which was extended to the ABCE model of floral development. This model has been validated in many dicot species using genetic transformation studies and mutant analyses. Many dicot flowers have two distinctive perianth whorls, which include greenish sepals and showy petals. By contrast, the monocot lily flower has two almost identical petaloid whorls, the inner and outer tepals. To explain this type of floral morphology, a modified ABC model, the further extended modified ABCE model, was proposed. According to this model, B-class genes are expressed in whorls 1-3, and whorls 1 and 2 form petaloid structures. This review describes the molecular mechanisms regulating flower development in monocots. Since the showy perianth is one of the most important traits in floricultural crops, we focused on the B-and C-class genes, which are related to the development and modification of the perianth. The review describes the expression patterns of floral organ identity genes, and presents functional studies using double-flowered and viridiflora cultivars in some monocot species. Besides lily-type flowers, there are several types of monocot flower, such as commelina type with two whorls of distinctive perianth, orchid and grass flowers. The review also describes the molecular analyses of these types of monocot flower.

Expression Pattern and Functional Characterization of PISTILLATA Ortholog Associated With the Formation of Petaloid Sepals in Double-Flower Eriobotrya japonica (Rosaceae)

“…the petaloid sepals (Singh et al, 2014). In the flowers of monocot such as Zingiberales, Commelinales, Alismatales, and Liliales, expanded expression of class B genes into the first floral whorl was correlated with the formation of petaloid organs (Kanno et al, 2007;Hsu et al, 2015;Kanno, 2015;. These results suggested that altering expression pattern of PI orthologous genes caused the transformation from sepal to petaloid organ in flowers.…”

Expression and Functional Analyses of Five B-class Genes in the Grape Hyacinth (<i>Muscari armeniacum</i>)

“…Although preliminary RT-PCR analysis showed MaDEF2 expression in all whorls (referred as an unpublished data in Kanno, 2016;Kanno et al, 2007), this was likely because of an excess of PCR cycles in the RT-PCR. Overall, expression profiles of MaGLOA1 and MaDEF1 were consistent with those of the typical Bclass genes proposed in the modified ABC model (Kanno, 2016;Kanno et al, 2003;van Tunen et al, 1993). Among the remaining genes, MaGLOA2 and MaDEF2 seem to have supplemental or perhaps redundant functions, as the expression levels of these genes were low.…”

“…Genetic analysis of floral homeotic mutants of Arabidopsis thaliana and Antirrhinum majus has led to the classical ABC model (Coen and Meyerowitz, 1991;Weigel and Meyerowitz, 1994). This model explains the dicot floral structure comprising four floral organs, sepals, petals, ABC model to the ABCE model (Honma and Goto, 2001;Kanno, 2016;Pelaz et al, 2000Pelaz et al, , 2001.…”

“…Similarly, in Agapanthus praecox, two types of B-class genes (ApDEF and ApGLO) are expressed in the outer three whorls (Nakamura et al, 2005), which is consistent with the modified ABC model. Furthermore, the modified ABC model has been further extended to the modified ABCE model after the discovery of the E-function genes (Kanno, 2016;Soltis et al, 2007).…”

Phytoplasma-conserved phyllogen proteins induce phyllody across the Plantae by degrading floral MADS domain proteins

“…Flowers exhibit a wide variety of shapes and colors, and sometimes have abnormal phenotypes ( Meyer, 1966 ), including phyllody (replacement of floral organs by leaf-like structures) and double flowers (flowers with extra petals or petal-like structures). Plants with such abnormal flower phenotypes have often been used as commercial cultivars ( Kanno, 2016 ) and genetic resources to study molecular mechanisms of floral development ( Meyerowitz et al , 1989 ; Wellmer et al , 2014 ). In model eudicots such as Arabidopsis thaliana , the identity of floral organs is regulated by floral homeotic genes divided into ABCE-classes based on function (the ABCE-model): A- and E-class genes specify sepal identity; A-, B-, and E-class genes petal identity; B-, C-, and E-class genes stamen identity; and C- and E-class genes carpel identity ( Krizek and Fletcher, 2005 ; Soltis et al , 2007 ; Rijpkema et al , 2010 ).…”