부산대학교 도서관

In plants, clade A type 2C protein phosphatases (PP2CAs) have emerged as major players in abscisic acid (ABA)‐regulated stress responses by inhibiting protein kinase activity. However, how different internal and external environmental signals modulate the activity of PP2CAs are not well known. The transmembrane kinase (TMK) protein 4 (TMK4), one member of a previously identified receptor kinase subfamily on the plasma membrane that plays vital roles in plant cell growth, directly interacts with PP2CAs member (ABA‐Insensitive 2, ABI2). tmk4 mutant is hypersensitive to ABA in both ABA‐inhibited seed germination and primary root growth, indicating that TMK4 is a negative regulator in ABA signaling pathway. Further analyses indicate that TMK4 phosphorylates ABI2 at three conserved Ser residues, thus enhancing the activity of ABI2. The phosphorylation‐mimic ABI2S139DS140DS266D can complement but non‐phosphorylated form ABI2S139AS140AS266A cannot complement ABA hypersensitive phenotype of the loss‐of‐function mutant abi1‐2abi2‐2. This study provides a previously unidentified mechanism for positively regulating ABI2 by a plasma membrane protein kinase. [ABSTRACT FROM AUTHOR]