The role of GA-mediated signalling in the control of seed germination.

Seed germination is promoted by gibberellin (GA) in many plant species. Several GA signalling factors are known to induce the expression of genes encoding enzymes that mobilise food reserves, including starches, proteins and lipids, stored in the endosperm during seed germination. However, these factors do not control seed germination. Two recent reports have indicated that RGL1 and RGL2, both homologous to the GA-response height-regulating factors GAI/RGA/RHT/d8/SLR1/SLN1, are repressors of seed germination in Arabidopsis. These reports provide new clues as to how GA controls seed germination. The induction of RGL2 expression by imbibition and its repression by GA are of particular interest because they imply that RGL2 acts as an integrator of environmental and endogenous cues for germination