Arabidopsis KIN gamma subunit 1 has a potential to regulate activity of sucrose nonfermenting 1-related protein kinase 2s (SnRK2s) in vitro

To respond to environmental changes promptly, plants must regulate their signalling pathways with precision. Sucrose non fermenting1 (SNF1)-related protein kinases (SnRK) 2 are essential kinases in abiotic stress responses, including responses to abscisic acid (ABA). Although homologs of SnRKs in yeast require a γ-subunit for full activation, it has been unclear whether SnRK2s are affected by γ-subunits. In this report, we aimed to show the effect of Arabidopsis KIN gamma subunit 1 (KING1), which is a potential γ-subunit, on the activity of SnRK2. Recombinant KING1 bound to SnRK2.6 (a.k.a. OST1) and functionally inhibited its activity in vitro. On the other hand, KING1 facilitated the activity of SnRK2.2. Structural models suggest that significant structural changes occur as a result of KING1 binding to the C-terminal tail of SnRK2s. Since KING1 inhibits the kinase activity of a chimeric protein consisting of the N-terminal domain of SnRK2.6 and the C-terminal domain of SnRK2.2, the regulation by KING1 is determined by N-terminal domain of SnRK2s. Together, these results show that KING1 can mediate activity of SnRK2s in vitro.