Advances in Research on the Regulation of Floral Development by CYC-like Genes

Abstract

CYCLOIDEA (CYC)-like genes belong to the TCP transcription factor family and play important roles associated with flower development. The CYC-like genes in the CYC1, CYC2, and CYC3 clades resulted from gene duplication events. The CYC2 clade includes the largest number of members that are crucial regulators of floral symmetry. To date, studies on CYC-like genes have mainly focused on plants with actinomorphic and zygomorphic flowers, including Fabaceae, Asteraceae, Scrophulariaceae, and Gesneriaceae species and the effects of CYC-like gene duplication events and diverse spatiotemporal expression patterns on flower development. The CYC-like genes generally affect petal morphological characteristics and stamen development, as well as stem and leaf growth, flower differentiation and development, and branching in most angiosperms. As the relevant research scope has expanded, studies have increasingly focused on the molecular mechanisms regulating CYC-like genes with different functions related to flower development and the phylogenetic relationships among these genes. We summarize the status of research on the CYC-like genes in angiosperms, such as the limited research conducted on CYC1 and CYC3 clade members, the necessity to functionally characterize the CYC-like genes in more plant groups, the need for investigation of the regulatory elements upstream of CYC-like genes, and exploration of the phylogenetic relationships and expression of CYC-like genes with new techniques and methods. This review provides theoretical guidance and ideas for future research on CYC-like genes.

Keywords: CYC2 clade; CYCLOIDEA (CYC)-like gene; TCP gene family; floral symmetry; molecular regulatory mechanism; phylogeny.

Figure 1

Phylogenetic tree of selected CYC-like genes in angiosperms. The number beside each node is the bootstrap support value.

Figure 2

Flowers of Cadia purpurea and Lupinus nanus [60]. (A) Flower of Cadia purpurea with actinomorphic corolla. (B) Flowers of Lupinus nanus with zygomorphic corolla. Reprinted with permission from Ref. [60]. Copyright © 2023, Oxford University Press.

Figure 3

Capitulum and florets of a wild-type sunflower plant and two mutants [79]. (A,B) Wild-type sunflower with disc and ray florets. (C,D) dbl mutant with disc and ray florets. (E,F) tub mutant with disc and ray florets. The florets from the disc center to the peripheral florets are arranged from left to right. Reprinted with permission from Ref. [79]. Copyright © 2023 Chapman et al.

Figure 4

G. hybrida with GhCYC2a overexpression (A–C) and inhibition (D–F) [71]. (A) Disc florets (df) of wild-type (wt) Gerbera hybrida and transgenic (tr) G. hybrida with obvious phenotypic differences. St, stamen. (B) Pollen presentation on the style of the disc florets of wild-type G. hybrida. (C) Disc florets of transgenic G. hybrida lacking functional stamens. (D) Transitional floret (tf) of wild-type and transgenic G. hybrida. (E) Capitulum of wild-type G. hybrida. (F) Capitulum of genetically modified G. hybrida. Reprinted with permission from Ref. [71]. Copyright © 2023 by The National Academy of Sciences of the USA.

Figure 5

Knockdown of ClCYC2g expression adversely affects the formation of symmetrical marginal florets in the radiate capitulum in chrysanthemum [97]. (A,B) Morphology of the capitulum of wild-type (WT) and transgenic C. lavandulifolium. (C) Ray and disc florets of wild-type C. lavandulifolium. (D) Ray-shaped florets with gradually increasing mutations. Orange and blue arrows indicate abnormal petals and stamens, respectively. (E,F) Expanded marginal florets of the transgenic lines. White and blue arrows indicate the bilabiate corolla with a deeply dentate limb apex and stamens, respectively. Reprinted with permission from Ref. [97]. Copyright © 2023 Society for Experimental Biology and John Wiley & Sons Ltd. (Hoboken, American).

Figure 6

Flowers of wild-type and mutant snapdragon plants [1]. Photographs of the dorsal corolla lobe (d), lateral corolla lobe (l), and ventral corolla lobe (v) of the wild-type snapdragon flower are presented. The characteristics of the different corolla lobes are shown to the right of each flower. Reprinted with permission from Ref. [1]. Copyright © 2023, Nature Publishing Group.

Figure 7

Front and side view and floral diagram of normal and peloric flowers of Petrocosmea sinensis [54]. (A–C) Front and side view and floral diagram of P. sinensis normal flowers, which have a typical bilaterally symmetrical corolla. (D–F) Front and side view and floral diagram of P. sinensis peloric flowers, which have a radially symmetrical corolla. DP, dorsal corolla lobes; DS, dorsal stamens; LS, lateral stamens; LP, lateral corolla lobes; VS, ventral stamens; VP, ventral corolla lobe. Reprinted with permission from Ref. [54]. Copyright © 2023, Oxford University Press.

Figure 8

Morphology of Canna indica flowers and expression of CiTBL genes [142] (Yu et al., 2020). (A) Flower morphology. A: anthers; C: carpel; L: labellum; P: petals; PA: petaloid appendage; PS: petaloid staminodes; S: sepals; St: staminodes. (B) Expression of CiTBL1a, CiTBL1b-1, and CiTBL1b-2 in young inflorescences and flowers at different developmental stages. Gene expression sites are indicated in blue, with the intensity of the coloration reflecting the expression level. AS: abortive staminodes; B: primary bracts; CM: meristem of monochasium; CP: common primordium of the petal and stamen; FM: floral meristem; IM: inflorescence meristem. Reprinted with permission from Ref. [142]. Copyright © 2023 Frontiers Media S.A.