Flower Development and Regulation of Flowering (original) (raw)

Four concentric whorls around the flanks of the meristem develop to form a typical flower in angiosperms. From outer most to innermost, these four whorls are fated to become sepals, petals, stamens and ovary with two fused carpels. According to ABC model of flower development, three regions of floral meristem (A, B and C) and three types of genes (a, b and c) acting in these regions have regulatory functions. With the discovery of another class (E) of genes, a revised model, called ABCE model, was put forth which envisages four activities (A, B, C and E) around the four whorls in the flower. The specific function of four organs, namely, sepals, petals, stamens, and carpels, is based on the combination of these four activities in the flower. Initiation of flowering requires a shift from vegetative to reproductive phase. The multiprotein complexes of MADS-box proteins initiate the formation of concentric four whorls around the flower. The foremost step in reproduction is floral transition with the interplay activity of numerous external and internal signals. Flowers are derived from SAM. The emergence through environmental signals followed by changes in meristem and organ identity, stem cell termination and organogenesis mark the flower development process. The flower repression occurs only under specific environmental and developmental stage. Flowering time in non-inductive photoperiodic conditions need to be understood. The floral integrator gene Flowering locus T (FT) control flowering time in numerous plant species. FLOWERING LOCUS C (FLC) encodes a MADS domain protein that acts as a suppressor of flowering. The flowering time genes are involved in longday photoperiod, gibberellin, autonomous, and vernalization pathway. FLC regulation led to the emergence of chromatin-modifying systems that control the developmental shift from vegetative to flowering transition in plants. The suppressive H3K27me3 mark not only acts during floral induction by regulating FLC expression, and floral meristem recognition through leafy (LFY), it also contributes in the organogenesis during flower H3K4 demethylation, histone H3 Lysine-9 (H3K9) and H3 Lysine 27 (H3K27) methylation, and histone Arginine (R) methylation. The H3K4 hyper-trimethylation of FLC chromatin also corresponds to the flowering delay in winter-annual Arabidopsis. FLC in the Arabidopsis is suppressed by histone modifications through Vernalization 2 (VRN2) protein complex. The epigenetic factors reduce the flowering repression in winter to allow them to flower in spring season. Epigenetic modifications lead to the floral initiation and development through chromatin modifications under stress. The epigenetic mechanisms play vital role in the control of photoperiodic flowering. The genetic and epigenetic control on the complex network of flowering-regulatory mechanisms initiates flower formation in diverse plants, the understanding of which would be useful in future for elucidating the regulatory mechanism for better agricultural production.