Figure 8.

Proposed Model for Transphosphorylation between CDL1 and OST1 in Stomatal Closure.

In guard cells, ABA-triggered PP2C inhibition promotes OST1 binding to CDL1. Then, OST1 is fully activated by sequential transphosphorylation between OST1 and CDL1. When BR level is high, BR binding to the BRI1 receptor activates CDL1, thereby leading to CDL1 phosphorylation of OST1. BR activates CDL1 independently of OST1 whereas ABA activates CDL1 in an OST1-dependent manner. The circled “P” indicate phosphorylation (+P) or dephosphorylation (−P). BAK1-regulated OST1 phosphorylation was reported in previous work (Shang et al., 2016).