Figure 9.
Models for SMAX1 Regulation and the Functions of Its Major Domains.
(A) Activation of KAI2 by KAR or KL promotes its association with SCFMAX2 and SMAX1, resulting in proteolysis of SMAX1. Polyubiquitination of SMAX1 is presumed, but has not been demonstrated. This proposed mechanism is highly similar to the SL signaling mechanism. MAX2-independent degradation of SMAX1 also contributes to its turnover, at least in Arabidopsis. MAX2-independent degradation of KAI2 after KAR treatment can be explained by association of KAI2 with unstable SMAX1 and SMXL2 (not depicted). Ub, ubiquitin.
(B) Diagram of the major domains of the SMAX1 protein and their proposed functions. The amino acid numbers at the boundaries of each domain of Arabidopsis SMAX1 are indicated.