Fig. 11
A molecular framework for profilin-mediated activation of apical and reproductive meristem. Different roles of profilin are shown: (i) including its classical role in cellular architecture mainly through actin polymerization and depolymerization; cellular signalling mainly through actin-related proteins (ARPs). In association with ARPs, profilin polymerizes actin, and certain ARPs have also been reported for their role in flowering phenomenon. Also, ARP6 induces FLC gene expression leading to the repression of flowering [88, 89]. Such coordinated regulation of flowering time mainly through ARP genes with FLC1 regulator directly influence flower genes expression cascade. (ii) its novel roles in apical meristem determinacy via transcriptional activation of CLV1 gene in the homeodomain trans-factor WUS- dependent manner; and (iii) activation of key flowering regulators for floral development. The latter are known to largely initiate reproductive meristem activation through flowering time controlling genes such as flowering locus T4 (FT4) gene which travels from vegetative leaf cells to the initiating floral meristem and in turn up-regulates other flower controlling regulators mainly SOC1, LFY and ultimately AP1 which is a class ‘A’ gene and is responsible for the activation of class ‘B’ genes during floral development. Here, we identify important genes whose expression is directly induced by profilin overexpression that furthermore jointly regulate flower primordium initiation. These genes encode known regulators of flower development: FT4 gene, which specifies the flowering time, SOC1 transcription factor, which in collaboration with AGL24 and LEAFY (LFY) gene up-regulates AP1 gene, which is a class ‘A’ gene and works as a key regulator of floral development. In parallel, overexpression of profilin down-regulates negative flowering regulators: FLC1 gene, which suppresses the expression of SOC1 trans-factor; and FT1 gene, which acts as transcriptional inhibitor exclusively in tobacco [67]. Our study reveals a link between profilin and flower primordium initiation mainly via up-regulation of ARP genes