Protein: Shaggy-related protein kinase eta (EC 2.7.11.1) (ASK-eta) (Protein BRASSINOSTEROID INSENSITIVE 2) (Protein ULTRACURVATA 1) (Shaggy-related protein kinase 21) (AtSK21) (Q39011)
Organism: Arabidopsis thaliana (Mouse-ear cress)
Function: Negative regulator in brassinosteroid signal transduction pathway important for plant growth. May be also involved in auxin signaling pathway. Phosphorylates and increases the degradation of BZR1 and BZR2/BES1 by the proteasome. Phosphorylates BHLH150, beet curly top virus C4 and tomato golden mosaic virus AC4 on threonine and serine residues. Upon brassinosteroid signaling, inhibits stomatal development by phosphorylating and inhibiting the MAPKK kinase YDA and the MAPK kinases MKK4 and MKK5. Phosphorylates BSK1, BSK3, BSK5, BSK6, BSK8 and BSK11 in vitro. Phoyphorylates and destabilizes WRKY46, WRKY54 and WRKY70. Mediates BASL nuclear exclusion; kinase activity is required for this function. Required first at the cortical polarity site, to restrict MAPK signaling and promote asymmetric cell division (ACD), and second in the nucleus of stomatal lineage ground cells (SLGCs) or meristemoids, to limit cell division and to promote differentiation into pavement or stomatal guard cells, respectively, likely by initiating BASL polarization. Phosphorylates BASL, YDA and SPCH in vitro and POLAR in vivo. Phosphorylates and inhibits SPCH in the nucleus of SLGC undergoing ACD, thus negatively regulating stomatal development.
Subcellular location: Cytoplasm, cell cortex {ECO:0000269|PubMed:30429609}. Cytoplasm {ECO:0000269|PubMed:28652362, ECO:0000269|PubMed:30429609}. Nucleus {ECO:0000269|PubMed:28652362, ECO:0000269|PubMed:30429609}. Cell membrane {ECO:0000269|PubMed:28652362, ECO:0000269|PubMed:30429609}; Peripheral membrane protein {ECO:0000305}; Cytoplasmic side {ECO:0000305}. Note=Spotty cytoplasmic as well as nuclear localization (PubMed:28652362). Recruited to the plasma membrane by OPS (PubMed:28652362). Localized throughout the plasma membrane in asymmetric cell division (ACD) precursors (PubMed:30429609). Accumulates transiently in a polarized pattern at the plasma membrane immediately before ACD, relocalizing to well-defined foci, in a POLAR-dependent and in the presence of BASL (PubMed:30429609). Mostly abundant and more polarized at the cell cortex of stomatal lineage cells with asymmetric cell division (ACD) potential (PubMed:30429609). {ECO:0000269|PubMed:28652362, ECO:0000269|PubMed:30429609}.
Interaction partners:
- Protein BRASSINAZOLE-RESISTANT 1
- Protein BRASSINAZOLE-RESISTANT 2
- Serine/threonine-protein phosphatase BSU1
- BES1/BZR1 homolog protein 2
- Protein ABSCISIC ACID-INSENSITIVE 5
- BES1/BZR1 homolog protein 1
- Serine/threonine-protein kinase BSK1
- BRI1 kinase inhibitor 1
- Serine carboxypeptidase 24
- Shaggy-related protein kinase iota
Sequence:
MADDKEMPAAVVDGHDQVTGHIISTTIGGKNGEPKQTISYMAERVVGTGSFGIVFQAKCLETGETVAIKKVLQDRRYKNRELQLMRVMDHPNVVCLKHCFFSTTSKDELFLNLVMEYVPESLYRVLKHYSSANQRMPLVYVKLYMYQIFRGLAYIHNVAGVCHRDLKPQNLLVDPLTHQVKICDFGSAKQLVKGEANISYICSRFYRAPELIFGATEYTTSIDIWSAGCVLAELLLGQPLFPGENAVDQLVEIIKVLGTPTREEIRCMNPHYTDFRFPQIKAHPWHKIFHKRMPPEAIDFASRLLQYSPSLRCTALEACAHPFFDELREPNARLPNGRPFPPLFNFKQEVAGSSPELVNKLIPDHIKRQLGLSFLNQSGT