Constitutive activation and transgenic evaluation of the function of an arabidopsis PKS protein kinase.
A novel family of SOS2 (salt overly sensitive 2)-like protein kinase genes (designated PKSes) have been recently identified in Arabidopsis. The biochemical characteristics as well as in vivo roles of most of the PKSes are unclear at present. In this work, we isolated and characterized one of the PKSes, PKS18. PKS18 was expressed in leaves of mature Arabidopsis plants. The glutathione S-transferase (GST)-PKS18 fusion protein was inactive by itself in substrate phosphorylation. An activation loop Thr(169) to Asp mutation, however, highly activated this kinase in vitro (designated PKS18T/D). Kinase activity of the PKS18T/D preferred Mn(2+) to Mg(2+). The activated kinase showed a substrate specificity, and high catalytic efficiency for a peptide substrate p3 and for ATP. Interestingly, PKS18T/D transgenic plants were hypersensitive to the phytohormone abscisic acid (ABA) in seed germination and seedling growth, whereas silencing the kinase gene by RNA interference (RNAi) conferred ABA-insensitivity, indicating the involvement of PKS18 in plant ABA signaling.
Gong
Deming
D
Department of Plant Sciences, University of Arizona, Tucson 85721, USA.
Zhang
Changqing
C
Chen
Xiuyin
X
Gong
Zhizhong
Z
Zhu
Jian-Kang
JK
D000040:Abscisic Acid / Q000494:pharmacology; D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D034622:RNA Interference; D013329:Structure-Activity Relationship; D019076:Transgenes
D029681:Arabidopsis Proteins; D000040:Abscisic Acid; C406738:SOS2 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases