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. 2024 Nov 5;151(21):dev203027. doi: 10.1242/dev.203027

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© 2024. Published by The Company of Biologists Ltd

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.

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Fig. 1. — Gene regulatory networks (GRNs) involved from flower initiation to anthesis in Arabidopsis thaliana and Antirrhinum majus. (A) Schematics of four developmental milestones in flowering: establishment of inflorescence architecture, specification of floral organ identity, establishment of symmetry and establishment of flower colour. Inflorescence architecture is very similar between the two model species, as is the specification of floral organ identity, but differences emerge when floral symmetry and flower colour is established during the later stages of development. This results in the Antirrhinum flower being bilaterally symmetrical (zygomorphic) and coloured, while the Arabidopsis flower is radially symmetrical (actinomorphic) and unpigmented. br, bract; c, carpel; IM, inflorescence meristem; LM, lateral meristem; p, petal; s, sepal; st, stamen. (B-E) Simplified gene regulatory networks (GRNs) controlling four developmental pathways contributing to floral display. (B) The GRN controlling inflorescence architecture establishment in Arabidopsis, where the central regulator LFY is essential for activation of floral meristem identity. LFY is repressed in the inflorescence meristem by TFL1 to maintain indeterminacy of the inflorescence. Later in development, LFY and UFO interact to initiate expression of floral organ identity genes. AP1, APETALA 1; FM, floral meristem; IM, inflorescence meristem; LFY, LEAFY; SAM, shoot apical meristem; TFL1, TERMINAL FLOWER 1; UFO, UNUSUAL FLOWER ORGANS. (C) The GRN controlling floral organ identity specification in the Arabidopsis floral meristem, where the ABCE family transcription factors are expressed in overlapping domains, and in particular combinations, to specify the identity of different organs. A-function genes are green, B-function genes are purple, C-function genes are orange and E-function genes are blue. AG, AGAMOUS; AP1/3, APETALA 1/3; LFY, LEAFY; PI, PISTILLATA; SEP, SEPALLATA; UFO, UNUSUAL FLOWER ORGANS. (D) The GRN controlling establishment of flower symmetry in Antirrhinum, where the ventralising factor DIV is repressed in the dorsal parts of the flower by RAD. RAD itself is activated by dorsally expressed CYC. This ultimately results in the specification of dorsal, lateral and ventral petals. CYC, CYCLOIDEA; DICH, DICHOTOMA; DIV, DIVARICATA; RAD, RADIALIS. (E) The GRN controlling flower colour in Antirrhinum via anthocyanin production, where MBW complexes comprising different combinations of MYB and bHLH transcription factors and a scaffold protein (WDR) activate expression of genes encoding enzymes that drive red anthocyanin biosynthesis in different parts of the flower. ELUTA (EL), also a MYB protein, represses anthocyanin production in the petal lobes. A silencing RNA in the SULFUREA (SULF) locus results in yellow pigment being localised to the opening of the corolla tube. DEL, DELILA; INC1, INCOLORATA 1; ROS, ROSEA; VE, VENOSA; WDR, WD REPEAT PROTEINS.