Phosphorylation Status of B Beta Subunit Controls PP2A activity in Ethylene-mediated Root Growth Inhibition

The various combinations and regulations of different subunits of phosphatase PP2A holoenzymes underlie their functional complexity and importance. We identified a distinct PP2A holoenzyme composed of A2, Bβ and C4. Upon the ethylene treatment, Bβ subunit is dephosphorylated, leading to a tight formation of the A2-C4-Bβ protein complex. EIR1 is the target of the PP2A A2-C4-Bβ complex mediated by the A2 subunit. Importantly, the phosphorylation of Bβ subunit in the absence of ethylene leads to an inactivation of PP2A. As a result, EIR1 remains phosphorylated, and no root growth inhibition occurs. Upon the ethylene treatment, Bβ subunit is dephosphorylated, leading to an activation of PP2A to dephosphorylate EIR1, resulting in a root growth inhibition. Altogether, our research revealed a novel molecular mechanism by which the dephosphorylation of Bβ subunit switches on the PP2A activity to dephosphorylate EIR1, leading to a root growth inhibition in response to ethylene. ### Competing Interest Statement The authors have declared no competing interest.