The expression patterns of three class B genes in two distinctive whorls of petaloid tepals in Alstroemeria ligtu

Suppression of B function by chimeric repressor gene-silencing technology (CRES-T) reduces the petaloid tepal identity in transgenic Lilium sp

Some monocotyledonous plants, including liliaceous, amaryllidaceous and iridaceous ones, produce flowers with petaloid tepals in whorls 1 and 2 organs. For explaining the molecular mechanism of two-layered petaloid tepal development, the modified ABC model has been proposed, in which B class genes are expressed in whorl 1 organs as well as in whorls 2 and 3 organs. We have previously obtained results strongly support the modified ABC model by chimeric repressor gene-silencing technology (CRES-T)-mediated suppression of B function in the liliaceous plant Tricyrtis sp. In the present study, we introduced a CRES-T construct derived from the B class gene of Tricyrtis sp. (TrihDEFa-SRDX) into Lilium sp. in order to examine the effect of suppressing B function on the floral organ identity. Flowers of transgenic plants did not open fully and had pale pink-colored tepals with decreased numbers of papillae on the adaxial side in whorls 1 and 2 compared with those of non-transgenic plants. No apparent morphological alterations were observed in whorls 3 and 4 organs. Both the amount of total anthocyanins and the expression levels of endogenous flavonoid biosynthesis-related genes (LhMYB12, LhbHLH2, LhCHS, LhF3H, LhF3’H, LhDFR and LhANS) decreased in whorls 1 and 2 organs of transgenic plants compared with non-transgenic plants. In addition, the expression levels of endogenous B class genes (LFDEF, LFGLOA and LFGLOB) decreased in transgenic plants and the level was negatively correlated with the degree of morphological alteration. Thus suppression of B function may reduce the identity of petaloid tepals in whorls 1 and 2 of transgenic Lilium sp.

Expression pattern of ABCDE model genes in floral organs of bolting garlic clone

A correct understanding of the ABCDE model genes expression, especially genes involved in the development of the reproductive floral organs, in bolting and fertile garlic clones improves the process of its fertilization and breeding programs. Therefore, Real-Time PCR was employed to evaluate the temporal and spatial expression patterns of some floral organ identity genes in the inflorescence and different floret organs in the two stages of green and purple florets of bolting garlic clone. Relative expression of the studied genes, except AsSTK, in the mature inflorescence increased significantly during the early stages of initiation and differentiation of floral organs. Relative expression of the AsAP1 in the tepal and carpel, and AsAP2 in the tepal, stamen and carpel increased significantly. The highest relative expression levels of the AsAP1 and AsAP2 were found in the tepal of green florets and in the carpel of purple florets, respectively. AsAP3 and AsPI expression increased significantly in the stamen and carpel, and the highest relative expression of these two genes were observed in the green floret tepal. Relative expression of the AsAG increased significantly only in the reproductive floral organs and decreased significantly both in the carpel and stamen at floret maturity. The AsSEP1, 3 were expressed in all floral organs, but the AsSTK was only expressed in the carpel and its relative expression increased significantly at floret maturity. Finally, since considerable expression levels of the above genes were observed in the floral organs, these genes seem to be influential in the formation of floral organs in bolting garlic.

Petal, Sepal, or Tepal? B-Genes and Monocot Flowers

In petaloid monocots expansion of B-gene expression into whorl 1 of the flower results in two whorls of petaloid organs (tepals), as opposed to sepals in whorl 1 of typical eudicot flowers. Recently, new gene-silencing technologies have provided the first functional data to support this, in the genus Tricyrtis (Liliaceae).

Suppression of B function strongly supports the modified ABCE model in Tricyrtis sp. (Liliaceae)

B class MADS-box genes play important roles in petal and stamen development. Some monocotyledonous species, including liliaceous ones, produce flowers with petaloid tepals in whorls 1 and 2. A modified ABCE model has been proposed to explain the molecular mechanism of development of two-layered petaloid tepals. However, direct evidence for this modified ABCE model has not been reported to date. To clarify the molecular mechanism determining the organ identity of two-layered petaloid tepals, we used chimeric repressor gene-silencing technology (CRES-T) to examine the suppression of B function in the liliaceous ornamental Tricyrtis sp. Transgenic plants with suppressed B class genes produced sepaloid tepals in whorls 1 and 2 instead of the petaloid tepals as expected. In addition, the stamens of transgenic plants converted into pistil-like organs with ovule- and stigma-like structures. This report is the first to describe the successful suppression of B function in monocotyledonous species with two-layered petaloid tepals, and the results strongly support the modified ABCE model.

Analysis of the floral MADS-box genes from monocotyledonous Trilliaceae species indicates the involvement of SEPALLATA3-like genes in sepal-petal differentiation

The evolution of greenish sepals from petaloid outer tepals has occurred repeatedly in various lineages of non-grass monocots. Studies in distinct monocot species showed that the evolution of sepals could be explained by the ABC model; for example, the defect of B-class function in the outermost whorl was linked to the evolution of sepals. Here, floral MADS-box genes from three sepal-bearing monocotyledonous Trilliaceae species, Trillium camschatcense, Paris verticillata, and Kinugasa japonica were examined. Unexpectedly, expression of not only A- but also B-class genes was detected in the sepals of all three species. Although the E-class gene is generally expressed across all floral whorls, no expression was detected in sepals in the three species examined here. Overexpression of the E-class SEPALLATA3-like gene from T. camschatcense (TcamSEP) in Arabidopsis thaliana produced phenotypes identical to those reported for orthologs in other monocots. Additionally, yeast hybrid experiments indicated that TcamSEP could form a higher-order complex with an endogenous heterodimer of B-class APETALA3/DEFICIENS-like (TcamDEF) and PISTILLATA/GLOBOSA-like (TcamGLO) proteins. These results suggest a conserved role for Trilliaceae SEPALLATA3-like genes in functionalization of the B-class genes, and that a lack of SEPALLATA3-like gene expression in the outermost whorl may be related to the formation of greenish sepals.

When ABC becomes ACB

Understanding how the information contained in genes is mapped onto the phenotypes, and deriving formal frameworks to search for generic aspects of developmental constraints and evolution remains one of the main challenges of contemporary biological research. The Mexican endemic triurid Lacandonia schismatica (Lacandoniaceae), a mycoheterotrophic monocotyledonous plant with hermaphroditic reproductive axes is alone among 250,000 species of angiosperms, as it has central stamens surrounded by a peripheral gynoecium, representing a natural instance of a homeotic mutant. Based on the classical ABC model of flower development, it has recently been shown that the B-function gene APETALA3 (AP3), essential for stamen identity, was displaced toward the flower centre in L. schismatica (ABC to ACB) from the early stages of flower development. A functional conservation of B-function genes from L. schismatica through the rescue of B-gene mutants in Arabidopsis thaliana, as well as conserved protein interactions, has also been demonstrated. Thus, it has been shown that relatively simple genetic alterations may underlie large morphological shifts fixed in extant natural populations. Nevertheless, critical questions remain in order to have a full and sufficient explanation of the molecular genetic mechanisms underlying L. schismatica's unique floral arrangement. Evolutionary approaches to developmental mechanisms and systems biology, including high-throughput functional genomic studies and models of complex developmental gene regulatory networks, constitute two main approaches to meet such a challenge. In this review, the aim is to address some of the pending questions with the ultimate goal of investigating further the mechanisms of L. schismatica's unique homeotic flower arrangement and its evolution.

Reduced transcription of a LEAFY-like gene in Alstroemeria sp. cultivar Green Coral that cannot develop floral meristems

Alstroemeria sp. cv. Green Coral has numerous bracts instead of flowers, and its cyme structures are repeated eternally. Observations of the development and morphology of inflorescence in cv. Green Coral revealed that transition from inflorescence to floral meristem was restricted. We isolated and characterized floral meristem identity genes LEAFY-like (AlsLFY) and SQUAMOSA-like (AlsSQa and AlsSQb) genes from Alstroemeria ligtu. In situ hybridization results indicated that AlsSQa and AlsSQb were expressed in the dome-shaped floral meristems and all floral organ primordia in A. ligtu. Transcripts of AlsLFY accumulated early in the dome-shaped floral meristems; the signals were restricted later to the outer region of the floral meristem. These results indicate that AlsLFY, AlsSQa, and AlsSQb function as floral meristem identity genes. Expression profiles of AlsLFY, AlsSQa, AlsSQb, and other MADS-box genes were compared between A. ligtu and cv. Green Coral. AlsLFY, AlsDEFa, and AlsAGL6 transcripts were not detected at the shoot apices of cv. Green Coral but were detected in A. ligtu. The early induction and accumulation of AlsLFY transcripts in the inflorescence meristem of A. ligtu prior to development of the floral meristem suggest that downregulation of AlsLFY is likely to restrict the inflorescence-to-floral meristem transition in cv. Green Coral.

Functional analysis of B and C class floral organ genes in spinach demonstrates their role in sexual dimorphism

BACKGROUND

Evolution of unisexual flowers entails one of the most extreme changes in plant development. Cultivated spinach, Spinacia oleracea L., is uniquely suited for the study of unisexual flower development as it is dioecious and it achieves unisexually by the absence of organ development, rather than by organ abortion or suppression. Male staminate flowers lack fourth whorl primordia and female pistillate flowers lack third whorl primordia. Based on theoretical considerations, early inflorescence or floral organ identity genes would likely be directly involved in sex-determination in those species in which organ initiation rather than organ maturation is regulated. In this study, we tested the hypothesis that sexual dimorphism occurs through the regulation of B class floral organ gene expression by experimentally knocking down gene expression by viral induced gene silencing.

RESULTS

Suppression of B class genes in spinach resulted in the expected homeotic transformation of stamens into carpels but also affected the number of perianth parts and the presence of fourth whorl. Phenotypically normal female flowers developed on SpPI-silenced male plants. Suppression of the spinach C class floral organ identity gene, SpAG, resulted in loss of reproductive organ identity, and indeterminate flowers, but did not result in additional sex-specific characteristics or structures. Analysis of the genomic sequences of both SpAP3 and SpPI did not reveal any allelic differences between males and females.

CONCLUSION

Sexual dimorphism in spinach is not the result of homeotic transformation of established organs, but rather is the result of differential initiation and development of the third and fourth whorl primordia. SpAG is inferred to have organ identity and meristem termination functions similar to other angiosperm C class genes. In contrast, while SpPI and SpAP3 resemble other angiosperms in their essential functions in establishing stamen identity, they also appear to have an additional function in regulating organ number and identity outside of the third whorl. We present a model for the evolution of dioecy in spinach based on the regulation of B class expression.

Isolation and characterization of the plant glsA promoter from Alstroemeria

The differentiation of a vegetative cell and a generative cell is a critical event during pollen development. The Lilium GlsA is known to localize in pollen and is considered to be involved in development of the generative cell. Here, we cloned a glsA ortholog from Alstroemeria, a commercially important cut flower. The expression of AaglsA (Alstroemeria aurea glsA) transcripts increased gradually after pollen mitosis I (PMI) and reached a significant level when the generative cell started to elongate. Analysis of the promoter of AaglsA suggests that AaglsA expression is controlled by several cis-regulatory elements during pollen development. This is the first investigation of reproductive factors regulating male gametogenesis in Alstroemeria.