The G protein-casein kinase 2 module acts as a pivot in plasma membrane-to-nucleus CLAVATA signaling to control shoot apical meristem size

The canonical CLAVATA3 (CLV3)-WUSCHEL (WUS) feedback loop functions in shoot apical meristem (SAM) maintenance that directly determines angiosperm shoot architecture and crop yield. However, how CLV3 signaling is transmitted into the nucleus to inhibit WUS expression remains a long-standing mystery. Here, we found that the Cucumis sativus CLV3 (CsCLV3) promotes the nuclear translocation of the CLV receptor-associated Gα protein CsGPA1. CsGPA1 directly interacts with the nuclear-localized protein kinase Casein Kinase II α subunit (CK2α). CK2α negatively regulates the SAM size in a kinase-dependent manner and CsGPA1 promotes the kinase activity of CsCK2α2. CsGPA1 and CsCK2α2 act in the same pathway to regulate SAM size by inhibiting the expression of WUS. Further, the GPA1-CK2α mediated signaling pathway is conserved in tomato SAM maintenance. Therefore, our results provide important new insights into the nature of the CLV3 signaling pathway that leads to WUS repression in plants.