Together with GSO2, receptor-like serine/threonine-kinase required during the development of the epidermal surface in embryos and cotyledons (PubMed:18088309). In coordination with GSO2, regulates root growth through control of cell division and cell fate specification. Controls seedling root growth by modulating sucrose response after germination (PubMed:24123341). Receptor of the peptide hormones CIF1 and CIF2 required for contiguous Casparian strip diffusion barrier formation in roots (PubMed:28104889). Required for localizing CASP proteins into the Casparian strip following an uninterrupted, ring-like domain, to trigger endodermal differentiation and thus regulate potassium ion (K) homeostasis. Involved in the maintenance of water transport and root pressure. May also be involved in the regulation of suberin accumulation in the endodermis (PubMed:25233277). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with CIF1 and CIF2. Localized into a broader band at the endodermal plasma membrane, embedding growing CASP microdomains. In endodermal cells, first observed on all cell sides, but quickly relocated in the transversal and anticlinal sides of the plasma membrane, but excluded from the Casparian strip membrane domain (CSD). Mostly expressed in siliques, seeds, developing embryos and seedlings, detected in flower buds and roots, but not in leaves or stems. In flower buds, localized in filaments and stigmas. During embryogenesis, uniform expression from the globular embryo to the mature cotyledonary embryo. After germination, detected in whole cotyledons and in the hypocotyl. During the 6 first days after germination (DAG), highly expressed in roots throughout the elongation zone (EZ) and differentiation zone, but restricted to the endodermis and vasculature. Accumulates progressively in the quiescent center (QC). Down-regulated at sites of lateral root primordia (LRP) initiation. Absent at sites of deliberate wounding in the root. Mostly observed in the inner layers of the mature root, the QC and shoot apical meristem (SAM) (PubMed:24123341). Expressed early during endodermal differentiation, shortly after the onset of endodermal cells elongation (PubMed:25233277). Repressed by wounding. Dramatic defect in endodermal barrier formation leading to altered potassium ion (K) homeostasis and hypersensitivity to low potassium conditions. Casparian strips are repeatedly interrupted, forming irregularly-sized holes of several micrometer in length, probably due to abnormal CASP proteins patterning. Suppresses the enhanced suberin production when combined to other Casparian strip-defective mutants such as esb1 and casp1 casp3. Extremely sensitive to changes in environmental conditions such as high temperatures and under long-day (LD) conditions leading to dwarf plants. Normal transpiration but altered water transport and root pressure (PubMed:25233277). No visible phenotype during embryogenesis and seedling development. Gso1 and gso2 double mutants produce slightly contorted seeds, with abnormally shaped embryos and seedlings; adhesion between cotyledons and the peripheral tissue of the endosperm, short hypocotyl, and concave cotyledons sometimes fused, with compressed epidermal cells, endosperm tissue partially adherent to the surface of the cotyledons, and a rough surface. In addition, seedlings of gso1 gso2 have also root growth and patterning defects characterized by abnormal numbers of cells in longitudinal files and radial cell layers, as well as aberrant stem cell division planes. Root growth arrest and cell divisions defects are rescued by exogenous application of sucrose, but not patterning defects (PubMed:24123341). The double mutant gso1 gso2 exhibits a repeatedly interrupted, discontinuous Casparian strip due to patch-like localization of the CASPs proteins as a result of partial fusion of individual CASP containing islands in the Casparian strip membrane domain (CSD) (PubMed:28104889). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.