OST1 activation by the brassinosteroid-regulated kinase CDG1-Like 1 in stomatal closure ($) (Plant Cell)

As gatekeepers between the outside world and the interior of the leaf, guard cells are extraordinarily sensitive to their environment. Closing keeps out pathogens and keeps in water vapor, but opening is needed to admit CO₂. The web of interactions that control stomatal aperture are also correspondingly complex. Although ABA is well known as a regulator of stomatal aperture, the role of BRs is less well understood. Kim et al. have identified a new convergence point between ABA and brassinosteroids in stomatal aperture. They show that the BR-regulated kinase CDG1-LIKE 1 (CDL1) interacts with and phosphorylates OST1, a key regulator of guard cell closure. They also show that both ABA and BR induce transphosphorylation between OST1 and CDL1. How this interaction fits in with BRs’ growth-regulatory functions remains to be determined. (Summary by Mary Williams) Plant Cell 10.1105/tpc.18.00239