Disease relevance of WAK1

• Further, transgenic plants overexpressing WAK1 showed an enhanced Al tolerance in terms of root growth when compared with the wild-type plants, making the WAK1 one of the important candidates for plant defense against Al toxicity [1].

High impact information on WAK1

• The level of WAK protein could be controlled by the concentration of the applied inducer, dexamethasone, and was correlated with the severity of the cell elongation inhibition phenotype [2].
• Moreover, exogenously added AtGRP-3 up-regulates the expression of Wak1, AtGRP-3, and PR-1 (for pathogenesis-related) in protoplasts [3].
• Interaction of the Arabidopsis receptor protein kinase Wak1 with a glycine-rich protein, AtGRP-3 [3].
• Further in vitro binding studies indicated that AtGRP-3 is the only isoform among the six tested AtGRPs that specifically interacts with Waks, and the cysteine-rich carboxyl terminus of AtGRP-3 is essential for its binding to Wak1 [3].
• Immunocytochemistry confirms that Wak1 is associated with the cell wall [4].

Biological context of WAK1

• In order to characterize further the interaction of WAK1 with pectin, a 564 bp DNA sequence corresponding to amino acids 67-254 of the extracellular domain of WAK1 from Arabidopsis thaliana was cloned and expressed as a soluble recombinant peptide in yeast [5].
• Previous work has shown that a reduction in WAK protein levels leads to a loss of cell expansion, indicating that these receptor-like proteins have a role in cell shape formation [6].
• An Arabidopsis cell wall-associated kinase required for invertase activity and cell growth [6].
• Short- and long-term analysis of gene expression in root fractions showed a typical "on" and "off" pattern with a first peak at 3 h of Al exposure followed by a sharp decline at 6 h and a complete disappearance after 9 h of Al exposure, suggesting the WAK1 is a further representative of Al-induced early genes [1].
• In this report, we used a receptor binding domain sequence-based prediction method to identify four putative binding sites in the extracellular domain of WAK1, in which cationic amino acids were selected for substitution by site-directed mutagenesis [7].

Anatomical context of WAK1

• WAK1 (wall-associated kinase 1) is a cytoplasmic serine/threonine kinase that spans the plasma membrane and extends into the extracellular region to bind tightly to the cell wall [8].
• The wall-associated kinases (WAK), a family of five proteins that contain extracellular domains that can be linked to pectin molecules of the cell wall, span the plasma membrane and have a cytoplasmic serine/threonine kinase domain [6].
• Wak1 fractionates with insoluble material when plant tissue is ground in a variety of buffers and detergents, suggesting a tight association with the plant extracellular matrix [4].

Associations of WAK1 with chemical compounds

• A glycine-rich secreted protein, AtGRP-3, was previously shown to regulate WAK1 functions through binding to the extracellular domain of WAK1 [9].
• Wak1 and AtGRP-3 are both induced by salicylic acid treatment [3].
• WAK is crosslinked into a detergent-insoluble complex within the cytoplasmic compartment before it appears on the cell surface, and this is independent of fucose modification or cellulose synthesis [10].

Other interactions of WAK1

• WAK1 and WAK2 are the most ubiquitously and abundantly expressed of the five tandemly arrayed genes, and their messages are present in vegetative meristems, junctions of organ types, and areas of cell expansion [11].
• In this study, we sought to determine the downstream molecules of the AtGRP-3/WAK1 signaling pathway, by using two-dimensional gel electrophoresis combined with Edman sequencing and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) [9].
• Here we report that PBS1 encodes a putative serine-threonine kinase [12].
• Involvement of a cell wall-associated kinase, WAKL4, in Arabidopsis mineral responses [13].

Analytical, diagnostic and therapeutic context of WAK1

• WAK1-specific reverse transcriptase-polymerase chain reaction analysis revealed an Al-induced WAK1 gene expression in roots [1].
• In vitro characterization of the homogalacturonan-binding domain of the wall-associated kinase WAK1 using site-directed mutagenesis [7].
• Elevated levels of WAK protein in root cells were observed through western blots after 6 h of Al exposure, indicating a lag time between the Al-induced WAK transcription and translation [1].

References