Fig. 8. Schematic model of the circuitry network regulating seed germination.
The model depicts ABI5 as a convergence node through which various independent or interdependent circuity networks regulate seed germination. In one network, germination is promoted through HY5 binding to BBX21 which, in turn binds to and sequester ABI5 required for the induction of its own gene. In the other, BBX19 binding to the GT1 motif induces ABI5 and thus suppresses germination. Lastly, enhanced GA levels leads to degradation of DELLA, that otherwise enhances ABA synthesis and block germination. The tightly controlled integration of these circuitries determines optimal timing of seed germination.