Floral Organ Identity Research Articles

Temperature-responsive module of OfAP1 and OfLFY regulates floral transition and floral organ identity in Osmanthus fragrans

The MADS-box transcription factor APETELA1 (AP1) is crucially important for reproductive developmental processes. The function of AP1 and the classic LFY-AP1 interaction in woody plants are not widely known. Here, the OfAP1-a gene from the continuously flowering plant Osmanthus fragrans ‘Sijigui’ was characterized, and its roles in regulating flowering time, petal number robustness and floral organ identity were determined using overexpression in Arabidopsis thaliana and Nicotiana tabacum. The expression of OfAP1-a was significantly induced by low ambient temperature and was upregulated with the floral transition process. Ectopic expression OfAP1-a revealed its classic function in flowering and flower ABC models. The expression of OfAP1-a is inhibited by LEAFY (OfLFY) through direct promoter binding, as confirmed by yeast one-hybrid and dual luciferase assays. Arabidopsis plants overexpressing OfAP1-a exhibited accelerated flowering and altered floral organ identities. Moreover, OfAP1-a-overexpressing plants displayed variable petal numbers. Likewise, the overexpression of OfLFY in Arabidopsis and Nicotiana altered petal number robustness and inflorescence architecture, partially by regulating native AP1 in transformed plants. Furthermore, we performed RNA-seq analysis of transgenic Nicotiana plants. DEGs were identified by transcriptome analysis, and we found that the expression of several floral homeotic genes was altered in both OfAP1-a and OfLFY-overexpressing transgenic lines. Our results suggest that OfAP1-a may play important roles during floral transition and development in response to ambient temperature. OfAP1-a functions as a petal number modulator and may directly activate a subset of flowers to regulate floral organ formation. OfAP1-a and OfLFY mutually regulate the expression of each other and coregulate genes that might be involved in these phenotypes related to flowering. The results provide valuable data for understanding the function of the LFY-AP1 module in the reproductive process and shaping floral structures in woody plants.

Arabidopsis leaf-expressed AGAMOUS-LIKE 24 mRNA systemically specifies floral meristem differentiation.

Plants can record external stimuli in mobile mRNAs and systemically deliver them to distal tissues to adjust development. Despite the identification of thousands of mobile mRNAs, the functional relevance of mobile mRNAs remains limited. Many mobile mRNAs are synthesized in the source cells that perceive environmental stimuli, but specifically exert their functions upon transportation to the recipient cells. However, the translation of mobile mRNA-encoded protein in the source cells could locally activate downstream target genes. How plants avoid ectopic functions of mobile mRNAs in the source cells to achieve tissue specificity remains to be elucidated. Here, we show that Arabidopsis AGAMOUS-LIKE 24 (AGL24) is a mobile mRNA whose movement is necessary and sufficient to specify floral organ identity. Although AGL24 mRNA is expressed in vegetative tissues, AGL24 protein exclusively accumulates in the shoot apex. In leaves, AGL24 proteins are degraded to avoid ectopically activating its downstream target genes. Our results reveal how selective protein degradation in source cells provides a strategy to limit the local effects associated with proteins encoded by mobile mRNAs, which ensures that mobile mRNAs specifically trigger systemic responses only in recipient tissues.

Evolutionary Dynamics of FLC-like MADS-Box Genes in Brassicaceae.

MADS-box genes encode transcription factors that play important roles in the development and evolution of plants. There are more than a dozen clades of MADS-box genes in angiosperms, of which those with functions in the specification of floral organ identity are especially well-known. From what has been elucidated in the model plant Arabidopsis thaliana, the clade of FLC-like MADS-box genes, comprising FLC-like genes sensu strictu and MAF-like genes, are somewhat special among the MADS-box genes of plants since FLC-like genes, especially MAF-like genes, show unusual evolutionary dynamics, in that they generate clusters of tandemly duplicated genes. Here, we make use of the latest genomic data of Brassicaceae to study this remarkable feature of the FLC-like genes in a phylogenetic context. We have identified all FLC-like genes in the genomes of 29 species of Brassicaceae and reconstructed the phylogeny of these genes employing a Maximum Likelihood method. In addition, we conducted selection analyses using PAML. Our results reveal that there are three major clades of FLC-like genes in Brassicaceae that all evolve under purifying selection but with remarkably different strengths. We confirm that the tandem arrangement of MAF-like genes in the genomes of Brassicaceae resulted in a high rate of duplications and losses. Interestingly, MAF-like genes also seem to be prone to transposition. Considering the role of FLC-like genes sensu lato (s.l.) in the timing of floral transition, we hypothesize that this rapid evolution of the MAF-like genes was a main contributor to the successful adaptation of Brassicaceae to different environments.

Dynamic cytological and transcriptomic analyses provide novel insights into the mechanisms of sex determination in Castanea henryi.

Castanea henryi is a monoecious woody food tree species whose yield and industrialization potential are limited by its low female-to-male flower ratio. Here, the male flowers on the male inflorescence of C. henryi were converted to female flowers by triple applications of exogenous cytokinin (CK) (N-(2-chloro-4-pyridyl)-N'-phenylurea, CPPU). To study the role of exogenous CK in flower sex determination, cytological and transcriptomic analyses were performed on samples from the five stages after CK treatment. Cytological analysis showed that stage 3 (nine days after the last CK treatment) was the critical stage in the differential development of the pistil primordium and stamen primordium. On this basis, one key module and two modules with significant positive correlations with stage 3 were identified by weighted gene co-expression network analysis (WGCNA), combined with transcriptome data. The CK and GA biosynthesis- and signaling-related genes, three transcription factor (TF) families, and 11 floral organ identity genes were identified in the related modules. In particular, the TFs WRKY47, ERF021, and MYB4, and floral organ identity genes AGL11/15, DEF, and SEP1 with large differences are considered to be critical regulators of sex determination in C. henryi. Based on these results, a genetic regulatory network for exogenous CK in the sex determination of flowers in C. henryi is proposed. This study contributes to the understanding of the role of CK in the sex regulation of flowers and provides new insights into the regulatory network of sex determination in C. henryi.

Genome-wide analysis of the MADS-box gene family in Lonicera japonica and a proposed floral organ identity model

BackgroundLonicera japonica Thunb. is widely used in traditional Chinese medicine. Medicinal L. japonica mainly consists of dried flower buds and partially opened flowers, thus flowers are an important quality indicator. MADS-box genes encode transcription factors that regulate flower development. However, little is known about these genes in L. japonica.ResultsIn this study, 48 MADS-box genes were identified in L. japonica, including 20 Type-I genes (8 Mα, 2 Mβ, and 10 Mγ) and 28 Type-II genes (26 MIKCc and 2 MIKC*). The Type-I and Type-II genes differed significantly in gene structure, conserved domains, protein structure, chromosomal distribution, phylogenesis, and expression pattern. Type-I genes had a simpler gene structure, lacked the K domain, had low protein structure conservation, were tandemly distributed on the chromosomes, had more frequent lineage-specific duplications, and were expressed at low levels. In contrast, Type-II genes had a more complex gene structure; contained conserved M, I, K, and C domains; had highly conserved protein structure; and were expressed at high levels throughout the flowering period. Eleven floral homeotic MADS-box genes that are orthologous to the proposed Arabidopsis ABCDE model of floral organ identity determination, were identified in L. japonica. By integrating expression pattern and protein interaction data for these genes, we developed a possible model for floral organ identity determination.ConclusionThis study genome-widely identified and characterized the MADS-box gene family in L. japonica. Eleven floral homeotic MADS-box genes were identified and a possible model for floral organ identity determination was also developed. This study contributes to our understanding of the MADS-box gene family and its possible involvement in floral organ development in L. japonica.

The regulation of chromatin configuration at AGAMOUS locus by LFR-SYD-containing complex is critical for reproductive organ development in Arabidopsis.

Switch defective/sucrose non-fermentable (SWI/SNF) chromatin remodeling complexes are evolutionarily conserved, multi-subunit machinery that play vital roles in the regulation of gene expression by controlling nucleosome positioning and occupancy. However, little is known about the subunit composition of SPLAYED (SYD)-containing SWI/SNF complexes in plants. Here, we show that the Arabidopsis thaliana Leaf and Flower Related (LFR) is a subunit of SYD-containing SWI/SNF complexes. LFR interacts directly with multiple SWI/SNF subunits, including the catalytic ATPase subunit SYD, in vitro and in vivo. Phenotypic analyses of lfr-2 mutant flowers revealed that LFR is important for proper filament and pistil development, resembling the function of SYD. Transcriptome profiling revealed that LFR and SYD shared a subset of co-regulated genes. We further demonstrate that the LFR and SYD interdependently activate the transcription of AGAMOUS (AG), a C-class floral organ identity gene, by regulating the occupation of nucleosome, chromatin loop, histone modification, and Pol II enrichment on the AG locus. Furthermore, the chromosome conformation capture (3C) assay revealed that the gene loop at AG locus is negatively correlated with the AG expression level, and LFR-SYD was functional to demolish the AG chromatin loop to promote its transcription. Collectively, these results provide insight into the molecular mechanism of the Arabidopsis SYD-SWI/SNF complex in the control of higher chromatin conformation of the floral identity gene essential to plant reproductive organ development.

SUPER WOMAN 2 (SPW2) maintains organ identity in spikelets by inhibiting the expression of floral homeotic genes OsMADS3, OsMADS58, OsMADS13, and DROOPING LEAF

Flower organ identity in rice is mainly determined by the A-, B-, C- and E-class genes, with the majority encoding MADS-box transcription factors. However, few studies have investigated how the expression of these floral organ identity genes is regulated during flower development. In this study, we identified a gene named SUPER WOMAN 2 (SPW2), which is necessary for spikelet/floret development in rice by participating in the regulation of the expression of pistil identity genes such as OsMADS3, OsMADS13, OsMADS58 and DL. In the spw2 mutant, ectopic stigma/ovary-like tissues were observed in the non-pistil organs, including sterile lemma, lemma, palea, lodicule, and stamen, suggesting that the identities of these organs were severely affected by mutations in SPW2. SPW2 was shown to encode a plant-specific EMF1-like protein that is involved in H3K27me3 modification as an important component of the PRC2 complex. Expression analysis showed that the SPW2 mutation led to the ectopic expression of OsMADS3, OsMADS13, OsMADS58, and DL in non-pistil organs of the spikelet. The ChIP-qPCR results showed significant reductions in the levels of H3K27me3 modification on the chromatin of these genes. Thus, we demonstrated that SPW2 can mediate the process of H3K27me3 modification of pistil-related genes to regulate their expression in non-pistil organs of spikelets in rice. The results of this study expand our understanding of the molecular mechanism by which SPW2 regulates floral organ identity genes through epigenetic regulation.

Combined genome-wide association studies and expression quantitative trait locus analysis uncovers a genetic regulatory network of floral organ number in a tree peony (Paeonia suffruticosa Andrews) breeding population.

Great progress has been made in our understanding of floral organ identity determination and its regulatory network in many species; however, the quantitative genetic basis of floral organ number variation is far less well understood for species-specific traits from the perspective of population variation. Here, using a tree peony (Paeonia suffruticosa Andrews, Paeoniaceae) cultivar population as a model, the phenotypic polymorphism and genetic variation based on genome-wide association studies (GWAS) and expression quantitative trait locus (eQTL) analysis were analyzed. Based on 24 phenotypic traits of 271 representative cultivars, the transcript profiles of 119 cultivars were obtained, which indicated abundant genetic variation in tree peony. In total, 86 GWAS-related cis-eQTLs and 3188 trans-eQTL gene pairs were found to be associated with the numbers of petals, stamens, and carpels. In addition, 19 floral organ number-related hub genes with 121 cis-eQTLs were obtained by weighted gene co-expression network analysis, among which five hub genes belonging to the ABCE genes of the MADS-box family and their spatial-temporal co-expression and regulatory network were constructed. These results not only help our understanding of the genetic basis of floral organ number variation during domestication, but also pave the way to studying the quantitative genetics and evolution of flower organ number and their regulatory network within populations.

Developmental and genetic basis of the androgynophore in Gynandropsis gynandra.

Flowering plants have evolved a vast array of floral features involved in plant-pollinator interactions. A feature that seemingly increases the chance of pollen transfer is the androgynophore, a stalk-like structure that raises the reproductive organs of the flower. However, little is known about the developmental and genetic basis of this structure despite its presence in multiple, distantly related taxa. Here, we address this gap by investigating Gynandropsis gynandra (Cleomaceae), a species with a prominent androgynophore. We combined morphological and anatomical analyses with a comparative transcriptomic study to provide a detailed description of the androgynophore throughout development, examine global gene expression patterns, and identify candidate genes putatively involved in androgynophore elongation. The radially symmetric androgynophore of G. gynandra rapidly lengthens primarily via cell elongation. Despite its structural uniformity, androgynophore development is characterized by complex gene expression patterns including differential expression of floral organ identity genes and genes associated with organ development and growth in Arabidopsis thaliana. Our morphological characterizations and high-quality transcriptome for G. gynandra suggest that the androgynophore is a novel structure formed via elaboration of both the receptacle and base of reproductive organs because it is structurally like an elongated internode but expresses the genetic repertoire typically associated with the reproductive organs. The drastic increase in cell length and uniform structure elevates the androgynophore as a potentially powerful model for cell elongation.

How flower development genes were identified using forward genetic screens in Arabidopsis thaliana.

In the later part of the 1980s, the time was ripe for identifying genes controlling flower development. In that pregenomic era, the easiest way to do this was to induce random mutations in seeds by chemical mutagens (or irradiation) and to screen thousands of plants for those with phenotypes specifically defective in floral morphogenesis. Here, we discuss the results of premolecular screens for flower development mutants in Arabidopsis thaliana, carried out at Caltech and Monash University, emphasizing the usefulness of saturation mutagenesis, multiple alleles to identify full loss-of-function, conclusions based on multiple mutant analyses, and from screens for enhancer and suppressor modifiers of original mutant phenotypes. One outcome was a series of mutants that led to the ABC floral organ identity model (AP1, AP2, AP3, PI, and AG). In addition, genes controlling flower meristem identity (AP1, CAL, and LFY), floral meristem size (CLV1 and CLV3), development of individual floral organ types (CRC, SPT, and PTL), and inflorescence meristem properties (TFL1, PIN1, and PID) were defined. These occurrences formed targets for cloning that eventually helped lead to an understanding of transcriptional control of the identity of floral organs and flower meristems, signaling within meristems, and the role of auxin in initiating floral organogenesis. These findings in Arabidopsis are now being applied to investigate how orthologous and paralogous genes act in other flowering plants, allowing us to wander in the fertile fields of evo-devo.

The Sapria himalayana genome provides new insights into the lifestyle of endoparasitic plants

BackgroundSapria himalayana (Rafflesiaceae) is an endoparasitic plant characterized by a greatly reduced vegetative body and giant flowers; however, the mechanisms underlying its special lifestyle and greatly altered plant form remain unknown. To illustrate the evolution and adaptation of S. himalayasna, we report its de novo assembled genome and key insights into the molecular basis of its floral development, flowering time, fatty acid biosynthesis, and defense responses.ResultsThe genome of S. himalayana is ~ 1.92 Gb with 13,670 protein-coding genes, indicating remarkable gene loss (~ 54%), especially genes involved in photosynthesis, plant body, nutrients, and defense response. Genes specifying floral organ identity and controlling organ size were identified in S. himalayana and Rafflesia cantleyi, and showed analogous spatiotemporal expression patterns in both plant species. Although the plastid genome had been lost, plastids likely biosynthesize essential fatty acids and amino acids (aromatic amino acids and lysine). A set of credible and functional horizontal gene transfer (HGT) events (involving genes and mRNAs) were identified in the nuclear and mitochondrial genomes of S. himalayana, most of which were under purifying selection. Convergent HGTs in Cuscuta, Orobanchaceae, and S. himalayana were mainly expressed at the parasite–host interface. Together, these results suggest that HGTs act as a bridge between the parasite and host, assisting the parasite in acquiring nutrients from the host.ConclusionsOur results provide new insights into the flower development process and endoparasitic lifestyle of Rafflesiaceae plants. The amount of gene loss in S. himalayana is consistent with the degree of reduction in its body plan. HGT events are common among endoparasites and play an important role in their lifestyle adaptation.

Pushing the boundaries of organ identity: Homology of the grass lemma

Pushing the boundaries of organ identity: Homology of the grass lemma

Deregulation of ζ-carotene desaturase in Arabidopsis and tomato exposes a unique carotenoid-derived redundant regulation of floral meristem identity and function.

A level of redundancy and interplay among the transcriptional regulators of floral development safeguards a plant's reproductive success and ensures crop production. In the present study, an additional layer of complexity in the regulation of floral meristem (FM) identity and flower development is elucidated linking carotenoid biosynthesis and metabolism to the regulation of determinate flowering. The accumulation and subsequent cleavage of a diverse array of ζ-carotenes in the chloroplast biogenesis 5 (clb5) mutant of Arabidopsis results in the reprogramming of meristematic gene regulatory networks establishing FM identity mirroring that of the FM identity master regulator, APETALA1 (AP1). The immediate transition to floral development in clb5 requires long photoperiods in a GIGANTEA-independent manner, whereas AP1 is essential for the floral organ development of clb5. The elucidation of this link between carotenoid metabolism and floral development translates to tomato exposing a regulation of FM identity redundant to and initiated by AP1 and proposed to be dependent on the E class floral initiation and organ identity regulator, SEPALLATA3 (SEP3).

Genome-Wide Analysis of MIKCC-Type MADS-Box Genes Reveals Their Involvement in Flower Development in Malus Lineage

MIKCC-type MADS-box genes are involved in floral organ identity determination but remain less studied in the Malus lineage. Based on the conserved domains of this gene family, we identified 341 genes among 13 species. Classification results showed that the MIKCC-type were generated later than the M-type, after the formation of Chlamydomonas reinhardtii. By phylogenetic analysis, three different groups were divided among 12 plant species, and one group was an ancestral MIKCC-type MADS-box homologous gene cluster from lower moss to higher flowering plants. Comparative analysis of these genes in A. thaliana and Malus lineages revealed a similar pattern evolutionary relationship with the phylogenetic analysis. Three classes of genes of the ABC model in A. thaliana had orthologous genes in the Malus species, but they experienced different evolutionary events. Only a whole-genome duplication (WGD) event was considered to act on the expansion of ABC-model-related genes in the Malus lineage. Additionally, the expression pattern of genes showed to be involved in flowering development stages and anther development processes among different M. domestica cultivars. This study systematically traced the evolutionary history and expansion mechanism of the MIKCC-type MADS-box gene family in plants. The results also provided novel insights for ABC model research of flower development in the Malus lineage.

Synchrotron micro-computed tomography unveils the three-dimensional structure and origin of staminodes in the Plains Prickly Pear Cactus Opuntia polyacantha Haw. (Cactaceae).

Floral appendages display an array of shapes and sizes. Among these organs, staminodes are morphologically diverse structures that have lost the ability to produce pollen, but in some instances, they produce fertile pollen grains. In the family Cactaceae staminodes are uncommon and range from simple linear to flat to spatulate structures, but studies describing their structural attributes are scanty. This study highlights the advantages of synchrotron radiation for sample preparation and as a research tool for plant biology. It describes the internal morphology of floral parts, particularly stamen, tepal, and staminode in the Plains Prickly Pear Cactus, Opuntia polyacantha, using synchrotron radiation micro-computed tomography (SR-μCT). It also shows the different anatomical features in reconstructed three-dimensional imaging of reproductive parts and discuss the advantages of the segmentation method to detect and characterize the configuration and intricate patterns of vascular networks and associated structures of tepal and androecial parts applying SR-μCT. This powerful technology led to substantial improvements in terms of resolution allowing a more comprehensive understanding of the anatomical organization underlying the vasculature of floral parts and inception of staminodes in O. polyacantha. Tepal and androecial parts have uniseriate epidermis enclosing loose mesophyll with mucilage secretory ducts, lumen, and scattered vascular bundles. Cryptic underlying structural attributes provide evidence of a vascularized pseudo-anther conjoint with tepals. The undefined contours of staminodial appendages (pseudo-anther) amalgamated to the tepals' blurred boundaries suggest that staminodes originate from tepals, a developmental pattern supporting the fading border model of floral organ identity for angiosperms.

Floral Homeotic Factors: A Question of Specificity.

MADS-domain transcription factors are involved in the control of a multitude of processes in eukaryotes, and in plants, they play particularly important roles during reproductive development. Among the members of this large family of regulatory proteins are the floral organ identity factors, which specify the identities of the different types of floral organs in a combinatorial manner. Much has been learned over the past three decades about the function of these master regulators. For example, it has been shown that they have similar DNA-binding activities and that their genome-wide binding patterns exhibit large overlaps. At the same time, it appears that only a minority of binding events lead to changes in gene expression and that the different floral organ identity factors have distinct sets of target genes. Thus, binding of these transcription factors to the promoters of target genes alone may not be sufficient for their regulation. How these master regulators achieve specificity in a developmental context is currently not well understood. Here, we review what is known about their activities and highlight open questions that need to be addressed to gain more detailed insights into the molecular mechanisms underlying their functions. We discuss evidence for the involvement of cofactors as well as the results from studies on transcription factors in animals that may be instructive for a better understanding of how the floral organ identity factors achieve regulatory specificity.

Flower transcriptional response to long term hot and cold environments in Antirrhinum majus.

Short term experiments have identified heat shock and cold response elements in many biological systems. However, the effect of long-term low or high temperatures is not well documented. To address this gap, we grew Antirrhinum majus plants from two-weeks old until maturity under control (normal) (22/16°C), cold (15/5°C), and hot (30/23°C) conditions for a period of two years. Flower size, petal anthocyanin content and pollen viability obtained higher values in cold conditions, decreasing in middle and high temperatures. Leaf chlorophyll content was higher in cold conditions and stable in control and hot temperatures, while pedicel length increased under hot conditions. The control conditions were optimal for scent emission and seed production. Scent complexity was low in cold temperatures. The transcriptomic analysis of mature flowers, followed by gene enrichment analysis and CNET plot visualization, showed two groups of genes. One group comprised genes controlling the affected traits, and a second group appeared as long-term adaptation to non-optimal temperatures. These included hypoxia, unsaturated fatty acid metabolism, ribosomal proteins, carboxylic acid, sugar and organic ion transport, or protein folding. We found a differential expression of floral organ identity functions, supporting the flower size data. Pollinator-related traits such as scent and color followed opposite trends, indicating an equilibrium for rendering the organs for pollination attractive under changing climate conditions. Prolonged heat or cold cause structural adaptations in protein synthesis and folding, membrane composition, and transport. Thus, adaptations to cope with non-optimal temperatures occur in basic cellular processes.

Identification of SHORT VEGETATIVE PHASE (SVP)-like genes and necessary responsibility of CmSVPc for the development of lateral branches in melon (Cucumis melo L.)

SVP acts as a central suppressor for floral transition and floral organ identity but also involves in the diverse functions among different species, such as abscission zones formation, plant height and dormancy. In this study, four SVP homologs were identified in melon and designated as CmSVPa, CmSVPb, CmSVPc and CmSVPd based on the similarity of their proteins to AtSVP. CmSVPc exhibited a clear difference in gene structure from the other CmSVP-like genes owing to its longer first and fifth introns. The results of exogenous gibberellin (GA3) and treatments with temperature and light suggested that CmSVPc and CmSVPd could be regulated by exogenous GA3 and all four CmSVPs involved in temperature and light responsive pathways. The results of RT-PCR indicated that transcripts of four CmSVPs were highly accumulated in shoot apices (MA and LA) and young leaves (YL) but they were present at relatively low levels in opening corolla (MF and BF). Compared with CmSVPa, CmSVPb and CmSVPd, the transcripts of CmSVPc were highest in all detected tissues except for LA in which CmSVPb accumulated to the highest level. Due to the specificity of gene structure and abundant transcripts of CmSVPc in melon, CmSVPc was chosen for further study. Subcellular localization revealed that CmSVPc was localized to the nucleus. Overexpression of CmSVPc in Arabidopsis led to increased numbers of lateral branches, delayed floral transition, and abnormal flower development compared with the wild type. However, CmSVPc-RNAi plants in melon inhibited the normal development of lateral branches, and the transgenic plants in which CmSVPc was downregulated also displayed shorter internodes, smaller petals and shorter fruits compared with the control. These results indicated that CmSVPc plays an important role in maintaining the growth of lateral branches in melon.

Systematic analysis of MADS-box gene family in the U's triangle species and targeted mutagenesis of BnaAG homologs to explore its role in floral organ identity in Brassica napus.

MADS-box transcription factors play an important role in regulating floral organ development and participate in environmental responses. To date, the MADS-box gene family has been widely identified in Brassica rapa (B. rapa), Brassica oleracea (B. oleracea), and Brassica napus (B. napus); however, there are no analogous reports in Brassica nigra (B. nigra), Brassica juncea (B. juncea), and Brassica carinata (B. carinata). In this study, a whole-genome survey of the MADS-box gene family was performed for the first time in the triangle of U species, and a total of 1430 MADS-box genes were identified. Based on the phylogenetic relationship and classification of MADS-box genes in Arabidopsis thaliana (A. thaliana), 1430 MADS-box genes were categorized as M-type subfamily (627 genes), further divided into Mα, Mβ, Mγ, and Mδ subclades, and MIKC-type subfamily (803 genes), further classified into 35 subclades. Gene structure and conserved protein motifs of MIKC-type MADS-box exhibit diversity and specificity among different subclades. Comparative analysis of gene duplication events and syngenic gene pairs among different species indicated that polyploidy is beneficial for MIKC-type gene expansion. Analysis of transcriptome data within diverse tissues and stresses in B. napus showed tissue-specific expression of MIKC-type genes and a broad response to various abiotic stresses, particularly dehydration stress. In addition, four representative floral organ mutants (wtl, feml, aglf-2, and aglf-1) in the T0 generation were generated by editing four AGAMOUS (BnaAG) homoeologs in B. napus that enriched the floral organ variant phenotype. In brief, this study provides useful information for investigating the function of MADS-box genes and contributes to revealing the regulatory mechanisms of floral organ development in the genetic improvement of new varieties.

The 1991 review by Coen and Meyerowitz on the war of the whorls and the ABC model of floral organ identity.

The 1991 review paper by Coen and Meyerowitz on the control of floral organ development set out the evidence available at that time, which led to the now famous ABC model of floral organ identity control. The authors summarised the genetic and molecular analyses that had been carried out in a relatively short time by several laboratories, mainly in Arabidopsis thaliana and Antirrhinum majus. The work was a successful example of how systematic genetic and molecular analysis can decipher the mechanism that controls a developmental process in plants. The ABC model is a combinatorial model in which each floral whorl acquires its identity through a unique combination of floral homeotic gene activities. The review also highlights the similarities in the regulation of floral organ identity between evolutionarily distant plant species, emphasising the general relevance of the model and paving the way for comprehensive studies of the evolution of floral diversity.