CYC-like Genes Research Articles

RETARDED PALEA1 Controls Palea Development and Floral Zygomorphy in Rice

Poaceae, one of the largest flowering plant families in angiosperms, evolved distinct inflorescence and flower morphology diverging from eudicots and other monocots. However, the mechanism underlying the specification of flower morphology in grasses remains unclear. Here we show that floral zygomorphy along the lemma-palea axis in rice (Oryza sativa) is partially or indirectly determined by the CYCLOIDEA (CYC)-like homolog RETARDED PALEA1 (REP1), which regulates palea identity and development. The REP1 gene is only expressed in palea primordium during early flower development, but during later floral stages is radially dispersed in stamens and the vascular bundles of the lemma and palea. The development of palea is significantly retarded in the rep1 mutant and its palea has five vascular bundles, which is similar to the vascular pattern of the wild-type lemma. Furthermore, ectopic expression of REP1 caused the asymmetrical overdifferentiation of the palea cells, altering their floral asymmetry. This work therefore extends the function of the TCP gene family members in defining the diversification of floral morphology in grasses and suggests that a common conserved mechanism controlling floral zygomorphy by CYC-like genes exists in both eudicots and the grasses.

Positive Selection and Expression Divergence Following Gene Duplication in the Sunflower CYCLOIDEA Gene Family

Members of the CYCLOIDEA (CYC)/TEOSINTE-BRANCHED1 (TB1) group of transcription factors have been implicated in the evolution of zygomorphic (i.e., bilaterally symmetric) flowers in Antirrhinum and Lotus and the loss of branching phenotype during the domestication of maize. The composite inflorescences of sunflower (Helianthus annuus L. Asteraceae) contain both zygomorphic and actinomorphic (i.e., radially symmetric) florets (rays and disks, respectively), and the cultivated sunflower has evolved an unbranched phenotype in response to domestication from its highly branched wild progenitor; hence, genes related to CYC/TB1 are of great interest in this study system. We identified 10 members of the CYC/TB1 gene family in sunflower, which is more than found in any other species investigated to date. Phylogenetic analysis indicates that these genes occur in 3 distinct clades, consistent with previous research in other eudicot species. A combination of dating the duplication events and linkage mapping indicates that only some of the duplications were associated with polyploidization. Cosegregation between CYC-like genes and branching-related quantitative trait loci suggest a minor, if any, role for these genes in conferring differences in branching. However, the expression patterns of one gene suggest a possible role in the development of ray versus disk florets. Molecular evolutionary analyses reveal that residues in the conserved domains were the targets of positive selection following gene duplication. Taken together, these results indicate that gene duplication and functional divergence have played a major role in diversification of the sunflower CYC gene family.

Significance of RT-PCR expression patterns of CYC-like genes in Oreocharis benthamii (Gesneriaceae)

We isolated and characterized two CYC-like genes from Oreocharis benthamii Clark (Gesneriaceae) in order to investigate their expression patterns. Phylogenetic analysis demonstrates that the two CYC-like genes, ObCYC1 and ObCYC2, belong to GCYC1 and GCYC2 clades in Gesneriaceae, respectively. Gene-specific RT-PCR results show that they have different spatio-temporal expression patterns. ObCYC1 is mainly expressed in the adaxial region of developing flowers as CYC is in Antirrhinum majus. The expression pattern of ObCYC1 demonstrates its basic function of controlling the adaxial floral organ development that is similar to that of CYC in Antirrhinum, which is in correlation with their conserved function domains, i.e. TCP and R domains. However, ObCYC1 is likely to repress the growth of both the adaxial petals and adaxial staminode. In addition, the weak- ened expression of ObCYC1 near flowering is correlated with the flower morphology of Oreocharis which is characteristic of weak zygomorphy. ObCYC2 exhibits a remarkable differentiation in protein sequence of TCP and R domain in comparison with those of ObCYC1 and CYC. Correlatively, ObCYC2 is inactive in floral tissue. This unique feature of ObCYC2 needs to be investigated by further comparative study both in expression and function in order to understand its basic function and evolutionary pathway in Gesneriaceae and related families.

Diversity and Evolution of CYCLOIDEA-Like TCP Genes in Relation to Flower Development in Papaveraceae

Monosymmetry evolved several times independently during flower evolution. In snapdragon (Antirrhinum majus), a key gene for monosymmetry is CYCLOIDEA (CYC), which belongs to the class II TCP gene family encoding transcriptional activators. We address the questions of the evolutionary history of this gene family and of possible recruitment of genes homologous to CYC in floral development and symmetry in the Papaveraceae. Two to three members of the class II TCP family were found in each species analyzed, two of which were CYC-like genes, on the basis of the presence of both the TCP and R conserved domains. The duplication that gave rise to these two paralogous lineages (named PAPACYL1 and PAPACYL2) probably predates the divergence of the two main clades within the Papaveraceae. Phylogenetic relationships among angiosperm class II TCP genes indicated that (1) PAPACYL genes were closest to Arabidopsis (Arabidopsis thaliana) AtTCP18, and a duplication at the base of the core eudicot would have given rise to two supplementary CYC-like lineages; and (2) at least three class II TCP genes were present in the ancestor of monocots and eudicots. Semiquantitative reverse transcription-polymerase chain reaction and in situ hybridization approaches in three species with different floral symmetry indicated that both PAPACYL paralogs were expressed during floral development. A pattern common to all three species was observed at organ junctions in inflorescences and flowers. Expression in the outer petals was specifically observed in the two species with nonactinomorphic flowers. Hypotheses concerning the ancestral pattern of expression and function of CYC-like genes and their possible role in floral development of Papaveraceae species leading to bisymmetric buds are discussed.

Diversification of CYCLOIDEA‐like TCP Genes in the Basal Eudicot Families Fumariaceae and Papaveraceae s.str.

CYCLOIDEA-like genes belong to the TCP family of transcriptional regulators and have been shown to control different aspects of shoot development in various angiosperm lineages, including flower monosymmetry in asterids and axillary meristem growth in monocots. Genes related to the CYC gene from ANTIRRHINUM show independent duplications in both asterids and rosids. However, it remains unclear to what extent this affected the evolution of flower symmetry and shoot branching in these and other eudicot lineages. Here, we show that CYC-like genes have also undergone duplications in two related Ranunculales families, Fumariaceae and Papaveraceae s.str. These families exhibit morphological diversity in flower symmetry and inflorescence architecture that is potentially related to functions of CYC-like genes. We present sequences of 14 CYC-related genes covering 9 genera. Phylogenetic analyses indicate the presence of three clades of CYC-like genes. Shared motifs in the region between the TCP and R domains of CYC-like genes between Fumariaceae, Papaveraceae s.str., and AQUILEGIA (Ranunculaceae) indicate that the observed duplications originated from a single CYC gene present in all Ranunculales. RT-PCR expression data suggest that gene duplication and diversification in Fumariaceae and Papaveraceae s.str. was accompanied by divergence in expression patterns.

Isolation and sequence analysis of two CYC-like genes, SiCYC1A and SiCYC1B, from zygomorphic and actinomorphic cultivars of Saintpaulia ionantha (Gesneriaceae)

Using the mTAIL-PCR method, we have isolated the two CYC-like genes, SiCYC1A and SiCYC1B, from zygomorphic and actinomorphic cultivars of Saintpaulia ionantha respectively in Gesneriaceae. The two genes, SiCYC1A and SiCYC1B, from the zygomorphic cultivar both contain the whole regulation domain, i.e. TCP and R domains. Therefore, they should be functional in the floral symmetry establishment, homologous with CYC in Antirrhinum majus. Unexpectedly, the two genes from the actinomorphic cultivar are identical to those from the zygomorphic in DNA sequence, respectively. Based on comparative analysis of the molecular alteration at CYC-like genes, which are responsible for the morphological transformation from zygomorphy to actinomorphy, we suggest that the two closely related genes SiCYC1A and SiCYC1B might be regulated by a common upstream regulator, whose change would result in silence of both SiCYC1A and SiCYC1B in controlling the development of the adaxial and lateral organs in a flower. In addition, an mTAIL-PCR method was shown to have the technological advantages of the unknown sequence for isolation.

Floral zygomorphy, the recurring evolution of a successful trait

The flowers of the primitive angiosperm plants were radially symmetrical (actinomorphic). Flowers with bilateral symmetry (zygomorphic) evolved in several clades independently as an adaptation to specialized methods of pollination and played an important role in the diversification of flowering plants. In the model species Antirrhinum majus (snapdragon), the related genes CYCLOIDEA (CYC) and DICHOTOMA (DICH) are key in the development of this trait. This raises the question of whether they played a role in the evolution of floral bilateral symmetry. To address this, the evolution of CYC in relation to the evolution of zygomorphy is being investigated. Phylogenetic and functional analyses of CYC-like genes are being carried out in groups either closely related to Antirhinum or in families where zygomorphy evolved as an independent event. In addition, the origin of zygomorphy is being studied by comparing the function of CYC-like genes in species with zygomorphic flowers with their function in species with radially symmetrical flowers.

Molecular evolution of cycloidea-like genes in Fabaceae.

The cycloidea (CYC) gene controls floral symmetry in snapdragon (Antirrhinum majus). We investigated the evolution of CYC-like genes in some species of legumes that have zygomorphic flowers. Two to four CYC-like genes were isolated from a single species. The results of NJ and ML analyses indicate that CYC-like genes in legumes group into two monophyletic clades; one group consists of eight CYC-like genes (Clade 1) and the other contains three CYC-like genes and TB1 of maize (Clade 2). These phylogenetic trees and the Shimodaira-Hasegawa test suggest that Clade 1 is a sister of the original CYC group (Clade 3). Moreover, the result of the GeneTree analysis showed that the CYC-like genes experienced repeated duplication events during the evolution of legumes. We herein speculate as to the role of CYC-like genes in legumes and discuss the evolutionary processes that these genes have undergone.