FIGURE 6.

A predicted model of the gene regulation network (GRN) involving DnAGL19 to control D. nobile flowering. High levels of DnAGL19 expression regulate flowering via FT-dependent and AP1-dependent pathways which are independent from each other. In the FT-dependent pathway, the HOS1-CO module responds to the environmental temperature cues to differentially regulate the expression of FT ortholog. Under conditions with higher environmental temperature (e.g., in spring), expression of HOS1 is activated by DnAGL19 and therefore results to down-regulation of FT ortholog probably duo to degradation of CO protein. In winter with long-term low temperature, the activation of HOS1 is suppressed and the FT ortholog is up-regulated, by which floral transition is promoted. On the other hand, activated expression of DnAGL19 also results in up-regulation of AP1 ortholog to promote the establishment of floral meristem identity, but the components upstream and/or downstream the AP1 ortholog remains to be clarified. The black solid lines indicate that the D. nobile orthologs of FT and AP1 have been verified to be functional in flowering regulation. The HOS1-CO-FT module (shown with gray solid lines) has been identified in A. thaliana (Jung et al., 2012; Lazaro et al., 2012) but has yet to be characterized in D. nobile. The black dashed lines show the regulations observed at the transcriptional level.