Isolation and characterization of the C-class MADS-box gene involved in the formation of double flowers in Japanese gentian

Abstract

BackgroundGenerally, double-flowered varieties are more attractive than single-flowered varieties in ornamental plants. Japanese gentian is one of the most popular floricultural plants in Japan, and it is desirable to breed elite double-flowered cultivars. In this study, we attempted to characterize a doubled-flower mutant of Japanese gentian. To identify the gene that causes the double-flowered phenotype in Japanese gentian, we isolated and characterized MADS-box genes.ResultsFourteen MADS-box genes were isolated, and two of them were C-class MADS-box genes (GsAG1 and GsAG2). Both GsAG1 and GsAG2 were categorized into the PLE/SHP subgroup, rather than the AG/FAR subgroup. In expression analyses, GsAG1 transcripts were detected in the second to fourth floral whorls, while GsAG2 transcripts were detected in only the inner two whorls. Transgenic Arabidopsis expressing GsAG1 lacked petals and formed carpeloid organs instead of sepals. Compared with a single-flowered gentian cultivar, a double-flowered gentian mutant showed decreased expression of GsAG1 but unchanged expression of GsAG2. An analysis of the genomic structure of GsAG1 revealed that the gene had nine exons and eight introns, and that a 5,150-bp additional sequence was inserted into the sixth intron of GsAG1 in the double-flowered mutant. This insert had typical features of a Ty3/gypsy-type LTR-retrotransposon, and was designated as Tgs1. Virus-induced gene silencing of GsAG1 by the Apple latent spherical virus vector resulted in the conversion of the stamen to petaloid organs in early flowering transgenic gentian plants expressing an Arabidopsis FT gene.ConclusionsThese results revealed that GsAG1 plays a key role as a C-functional gene in stamen organ identity. The identification of the gene responsible for the double-flowered phenotype will be useful in further research on the floral morphogenesis of Japanese gentian.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0569-3) contains supplementary material, which is available to authorized users.

RNA interference suppression of AGAMOUS and SEEDSTICK alters floral organ identity and impairs floral organ determinacy, ovule differentiation, and seed‐hair development in Populus

“…In Arabidopsis , flowers in strong ag mutants usually lose reproductive organs and have a ‘rose‐like’ phenotype with the stamens transformed to petals and the central gynoecium transformed to a sepal‐ or petal‐looking internal structure (Bowman et al ., ; Yanofsky et al ., ). Similar loss‐of‐function phenotypes in the eu AG / PLE lineage have been observed in other bisexual species, such as in Antirrhinum , petunia, California poppy ( Eschscholzia californica ), opium poppy ( Papaver somniferum ), Thalictrum thalictroides , Japanese gentian ( Gentiana scabra ), Nicotiana benthamiana , and apple ( Malus domestica ) (Davies et al ., ; Kapoor et al ., ; Yellina et al ., ; Hands et al ., ; Fourquin & Ferrándiz, ; Galimba et al ., ; Nakatsuka et al ., ; Klocko et al ., ), and also in dioecious species such as spinach ( Spinacia oleracea L.) (Sather et al ., ). Additionally, AG acts as an activator of the NOZZLE / SPOROCYTELESS gene and controls pollen formation at late stages of flower development in Arabidopsis (Ito et al ., , ; Wilson & Zhang, ).…”

Thermal Control Suitable for Increasing Petals in <i>Eustoma grandiflorum</i> (Raf.) Shinn.

“…Loss of expression of the Arabidopsis C-class gene AGAMOUS (AG) results in the conversion of stamens and carpels to petals and sepals, respectively and indeterminacy of the floral meristem, leading to double flowers with excess petals. The same mechanism as that of Arabidopsis can be adopted in some floricultural plants such as Ipomea nil, Gentiana scabra, and Thalictrum thalictroides (Galimba et al, 2012;Nakatsuka et al, 2015;Nitasaka, 2003). In the case of the double-flowered Eustoma, several theories have been postulated about the genetic mechanism.…”

Floral Morphology and MADS Gene Expression in Double-flowered Japanese Evergreen Azalea

“…Thus, attenuated Cclass function could increase petal development, inhibit stamen development, and also increase the floral organ number, which is consistent with the formation of double flowers. Double-flowered phenotypes result from C-function repression in a number of horticultural plants, including Gentiana scabra (Nakatsuka et al, 2015), Camellia japonica (Sun et al, 2014), Petunia hybrida (Noor et al, 2014), and Cyclamen persicum (Tanaka et al, 2013). Therefore, it is likely that the double flowers of Japanese azalea cultivars result from lost or impaired C-function genes.…”

“…In a doubleflowered mutant of Japanese gentian (G. scabra), in which the stamens are substituted with petals, GsAG1 expression was down-regulated by insertion of a Tgs1 (transposable element of G. scabra 1) in the intron of the GsAG1 gene (Nakatsuka et al, 2015). Similar to these reports, it is highly possible that the AG/PLE homolog of double-flowered azaleas carries a transposon insertion mutation on account of the very low expression of the AG/PLE homolog in all floral organs of azalea double flowers (Fig.…”