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.
Garden asparagus is one of the most important crops worldwide. Since this crop is dioecious and male plants generally have higher yields compared to female plants, several DNA markers for sex ...identification have been developed for acceleration of asparagus breeding. Among these markers, Asp1-T7sp and MSSTS710 were found to be effective in sex determination for many asparagus cultivars. However, we previously found that these markers were not completely suitable for sex identification in the purple asparagus cultivar ‘Pacific Purple’. There are two types of male individuals in this cultivar: One type is PP-m, which is identified the sex type by Asp1-T7sp and MSSTS710 markers, while the other type is PP-m* whose sex type is not identified by these markers. Since the sex identification markers are located on the non-recombining Y region, it was expected that the sequence around this region might be different between PP-m and PP-m*. In this study, the sequence of one of the sex-determining genes,
MSE1/AoMYB35/AspTDF1
, was analyzed, and a comparative analysis was conducted among PP-m and PP-m* of ‘Pacific Purple’,
A. officinalis
and related species
A. maritimus
. The results revealed that PP-m and PP-m* has the similar sequence of
MSE1/AoMYB35/AspTDF1
gene from
A. officinalis
and
A. maritimus
, respectively. ‘Pacific Purple’ is a cultivar developed through polycross hybrid from Italian landrace ‘Violetto d’Albenga’ (VA), suggesting that VA originated from an interspecific crossing between
A. officinalis
and
A. maritimus
and that the pollen parent used in ‘Pacific Purple’ breeding contained two types of male individuals with different
MSE1/AoMYB35/AspTDF1
sequence. As a result, PP-m and PP-m* of ‘Pacific Purple’ harbors the similar sequences of the
MSE1/AoMYB35/AspTDF1
gene from
A. officinalis
and
A. maritimus
, respectively.
In
, the E-class
(
) genes are generally expressed across all floral whorls. These genes play fundamental roles in floral organ fate determination during development by interacting with other ...MADS-box gene products, such as those from A-, B-, and C-class genes. However, the function of
genes in orchid remains obscure. Here, we analyzed a mutant orchid cultivar with greenish flowers in
and found that this phenotype is caused by the absence of SEP function. Wild type
flowers contain a column and two perianth whorls consisting of three greenish sepals, two white petals, and a lip (labellum). By contrast, the flowers of
cultivar 'Ryokusei' appear greenish, with three normal sepals in whorl 1, two greenish petals and a lip in whorl 2, and several sepaloid organs and a ventral column in whorls 3 and 4. We isolated two
-like genes (
and
) and two
-like genes (
and
) from wild type
and compared their expression in the wild type vs. the mutant cultivar.
and
were expressed in the column in the wild type, whereas these genes were expressed in the ventral column and in sepaloid organs that had been converted from a column in 'Ryokusei.'
and
were expressed in all floral organs in the wild type. However, in the mutant cultivar,
was expressed in all floral organs, while
expression was not detected. Thus, we analyzed the genomic structures of
in the wild type and 'Ryokusei' and identified a retrotransposon-like element in its first exon in 'Ryokusei.' Yeast two-hybrid assays demonstrated that HrSEP-1 interacts with HrDEF, HrAG-1, and HrAG-2. These results indicate that the mutant phenotype of 'Ryokusei' flowers is caused by the loss of function of
. Therefore, this gene plays an important role in column, lip, and petal development in
flowers.
The genus Asparagus comprises approximately 200 species, some of which are commercially cultivated, such as the garden asparagus (A. officinalis). Many Asparagus species, including A. officinalis, ...are dioecious and have been grouped into a subgenus distinct from that of hermaphroditic species. Although many interspecific crossings have been attempted to introduce useful traits into A. officinalis, only some of the dioecious species were found to be cross-compatible with A. officinalis. Here, molecular phylogenetic analyses were conducted to determine whether interspecific crossability is proportional to the genetic distance between the crossing pairs and to further clarify the evolutionary history of the Asparagus genus. A clade with all cross-compatible species and no cross-incompatible species was recovered in the phylogenetic tree based on analyses of non-coding cpDNA regions. In addition, a sex-linked marker developed for A. officinalis amplified a male-specific region in all cross-compatible species. The phylogenetic analyses also provided some insights about the evolutionary history of Asparagus; for example, by indicating that the genus had its origin in southern Africa, subsequently spreading throughout the old world through intensive speciation and dispersal. The results also suggest that dioecious species were derived from a single evolutionary transition from hermaphroditism in Asparagus. These findings not only contribute towards the understanding of the evolutionary history of the genus but may also facilitate future interspecific hybridization programs involving Asparagus species.
The dynamic activity of the serine/threonine kinase Akt is crucial for the regulation of diverse cellular functions, but the precise spatiotemporal control of its activity remains a critical issue. ...Herein, we present a photo-activatable Akt (PA-Akt) system based on a light-inducible protein interaction module of Arabidopsis thaliana cryptochrome2 (CRY2) and CIB1. Akt fused to CRY2phr, which is a minimal light sensitive domain of CRY2 (CRY2-Akt), is reversibly activated by light illumination in several minutes within a physiological dynamic range and specifically regulates downstream molecules and inducible biological functions. We have generated a computational model of CRY2-Akt activation that allows us to use PA-Akt to control the activity quantitatively. The system provides evidence that the temporal patterns of Akt activity are crucial for generating one of the downstream functions of the Akt-FoxO pathway; the expression of a key gene involved in muscle atrophy (Atrogin-1). The use of an optical module with computational modeling represents a general framework for interrogating the temporal dynamics of biomolecules by predictive manipulation of optogenetic modules.
•Sets of MADS-box genes were isolated from three sepal-bearing Trilliaceae species.•Sepal-specific loss of E-class SEP3-like gene expression was found in all species.•Molecular analyses indicated a ...role for SEP3-like gene in normal B-class function.•Relation between the SEP3-like gene nonexpression and sepal formation was discussed.
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.
Asparagus kiusianus is a disease-resistant dioecious plant species and a wild relative of garden asparagus (Asparagus officinalis). To enhance A. kiusianus genomic resources, advance plant science, ...and facilitate asparagus breeding, we determined the genome sequences of the male and female lines of A. kiusianus. Genome sequence reads obtained with a linked-read technology were assembled into four haplotype-phased contig sequences (∼1.6 Gb each) for the male and female lines. The contig sequences were aligned onto the chromosome sequences of garden asparagus to construct pseudomolecule sequences. Approximately 55,000 potential protein-encoding genes were predicted in each genome assembly, and ∼70% of the genome sequence was annotated as repetitive. Comparative analysis of the genomes of the two species revealed structural and sequence variants between the two species as well as between the male and female lines of each species. Genes with high sequence similarity with the male-specific sex determinant gene in A. officinalis, MSE1/AoMYB35/AspTDF1, were presented in the genomes of the male line but absent from the female genome assemblies. Overall, the genome sequence assemblies, gene sequences, and structural and sequence variants determined in this study will reveal the genetic mechanisms underlying sexual differentiation in plants, and will accelerate disease-resistance breeding in garden asparagus.
Summary
Habenaria radiata (Orchidaceae) has two whorls of perianth, comprising three greenish sepals, two white petals and one lip (labellum). By contrast, the pseudopeloric (with a decreased degree ...of zygomorphy) mutant cultivar of H. radiata, ‘Hishou’, has changes in the identities of the dorsal sepal to a petaloid organ and the two ventral sepals to lip‐like organs. Here, we isolated four DEFICIENS‐like and two AGL6‐like genes from H. radiata, and characterized their expression. Most of these genes revealed similar expression patterns in the wild type and in the ‘Hishou’ cultivar, except HrDEF‐C3. The HrDEF‐C3 gene was expressed in petals and lip in the wild type but was ectopically expressed in sepal, petals, lip, leaf, root and bulb in ‘Hishou’. Sequence analysis of the HrDEF‐C3 loci revealed that the ‘Hishou’ genome harbored two types of HrDEF‐C3 genes: one identical to wild‐type HrDEF‐C3 and the other carrying a retrotransposon insertion in its promoter. Genetic linkage analysis of the progeny derived from an intraspecific cross between ‘Hishou’ and the wild type demonstrated that the mutant pseudopeloric trait was dominantly inherited and was linked to the HrDEF‐C3 gene carrying the retrotransposon. These results indicate that the pseudopeloric phenotype is caused by retrotransposon insertion in the HrDEF‐C3 promoter, resulting in the ectopic expression of HrDEF‐C3. As the expression of HrAGL6‐C2 was limited to lateral sepals and lip, the overlapping expression of HrDEF‐C3 and HrAGL6‐C2 is likely to be responsible for the sepal to lip‐like identity in the lateral sepals of the ‘Hishou’ cultivar.
Significance Statement
Unlike wild‐type Habenaria radiata flowers, which have a single modified medial petal formed into a lip, the mutant cultivar ‘Hishou’ flowers exhibit two additional lip‐like organs replacing the lateral sepals. Here, we identified the Hret2 retrotransposon insertion in the HrDEF‐C3 gene promoter as the cause of the pseudopeloric phenotype of ‘Hishou’. Based on DEF‐ and AGL6‐like gene expression patterns in the wild type and ‘Hishou’, the differential dorsoventral expression of the HrAGL6‐C2 gene is correlated with the transformation of lateral sepals into lip‐like structures.
Dioecy is a plant mating system in which individuals of a species are either male or female. Although many flowering plants evolved independently from hermaphroditism to dioecy, the molecular ...mechanism underlying this transition remains largely unknown. Sex determination in the dioecious plant Asparagus officinalis is controlled by X and Y chromosomes; the male and female karyotypes are XY and XX, respectively. Transcriptome analysis of A. officinalis buds showed that a MYB‐like gene, Male Specific Expression 1 (MSE1), is specifically expressed in males. MSE1 exhibits tight linkage with the Y chromosome, specific expression in early anther development and loss of function on the X chromosome. Knockout of the MSE1 orthologue in Arabidopsis induces male sterility. Thus, MSE1 acts in sex determination in A. officinalis.
A MYB‐like gene, MSE1, located on the Y chromosome and mutated on the X, acts in sex determination by inducing male‐specific anther development in Asparagus officinalis.
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