Figure 12.

Model for Positive Feedback Regulation of ABA Signaling via Induction of ICME Expression and Demethylation (i.e., Inactivation) of Isoprenylated Negative Regulators of ABA Signaling.

ABA promotes seed dormancy and stomatal closure but also increases the expression of the ICME gene, a positive regulator of ABA signaling. To date, the only isoprenylated negative regulators of ABA signaling to be identified are ROP2 and ROP6 (Lemichez et al., 2001; Li et al., 2001). Consequently, the isoprenylated protein shown is modified by a geranylgeranyl moiety and represents either ROP2 or ROP6. However, at least one unidentified farnesylated negative regulator of ABA signaling also exists in Arabidopsis. A hypothetical integral membrane isoprenylprotein receptor is shown.