Disease relevance of OST1

• Here, we report successful purification of OST1 produced in Escherichia coli: The protein is active and autophosphorylates [1].
• The data suggested the involvement of two novel extracellular serine proteases, nodulin-like proteins and an Arabidopsis thaliana OPEN STOMATA 1 (AtOST1) homolog in signaling fiber-cell death, as well as mechanisms responsible for hormonal control, nutrient remobilization, regulation of vacuolar integrity and autolysis of the dying fibers [2].

High impact information on OST1

• Stomatal guard cells of Arabidopsis perceive bacterial surface molecules, which requires the FLS2 receptor, production of nitric oxide, and the guard-cell-specific OST1 kinase [3].
• In-gel assays indicated that OST1 is an ABA-activated protein kinase related to the Vicia faba ABA-activated protein kinase (AAPK) [4].
• Arabidopsis OST1 protein kinase mediates the regulation of stomatal aperture by abscisic acid and acts upstream of reactive oxygen species production [4].
• The relative positions of ost1 and the other ABA-insensitive mutations in the ABA signaling network (abi1-1, abi2-1, and gca2) are discussed [4].
• ABA-induced ROS production was disrupted in ost1 guard cells, whereas applied H(2)O(2) or calcium elicited the same degree of stomatal closure in ost1 as in the wild type [4].

Biological context of OST1

• Our results further indicate that JAR1, as OST1, functions upstream of ROS produced by NAD(P)H oxidases and that the cytoplasmic alkalization precedes ROS production during MJ or ABA signal transduction in guard cells [5].
• Sequence analysis delineates two conserved boxes located in the carboxy-terminal moiety of OST1 after the catalytic domain: the SnRK2-specific box (glutamine-303 to proline-318) and the ABA-specific box (leucine-333 to methionine-362) [1].
• Our results showed that despite the resemblance between the corresponding Vicia and Arabidopsis proteins, it appears that the function of UBA2a is independent of OST1 phosphorylation [6].

Associations of OST1 with chemical compounds

• These results suggest that OST1 acts in the interval between ABA perception and ROS production [4].
• Site-directed mutagenesis and serial deletions reveal that serine (Ser)-175 in the activation loop and the SnRK2-specific box are critical for the activity of recombinant OST1 kinase [1].

Other interactions of OST1

• OST1 encodes a protein kinase involved in ABA-mediated stomatal closure while ABA2 encodes an enzyme involved in ABA biosynthesis [7].
• A recent report shows that mutations in the OST1 gene, encoding a serine-threonine protein kinase, render Arabidopsis thaliana guard cells insensitive to abscisic acid, such that stomata remain open in the presence of this phytohormone [8].

Analytical, diagnostic and therapeutic context of OST1

• Remarkably, ost1 and ost2 represent, to our knowledge, the first Arabidopsis mutations altering ABA responsiveness in stomata and not in seeds [9].

References