Protein Tyrosine Phosphatases: Implications in the Regulation of Stress Responses in Plants

Tyrosine phosphorylation is widely reported in animals as compared to plant systems. It is regulated by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). Plant systems exhibit a preference for serine/threonine residues for phosphorylation. Not many plant PTPs have been identified in plants similar to PTKs, despite the fact that tyrosine phosphorylation has a significant presence in plants. The identification of phosphorylated tyrosine residues and phosphotyrosine binding domains indicates that tyrosine phosphorylation is carried out by dual-specificity kinases or by phosphorylation at multiple sites. The PTPs are involved in redox regulation of enzymes, thus, creating a molecular switch to regulate signaling pathways. The higher number of DsPTPs and their substrate affinities implicate them in metabolism and stress signaling. The involvement of PTP superfamily in MAP kinase signaling pathways fine-tunes plant responses to various environmental and physiological stimuli. The limited PTP complement is indicative of functional overlap and a varied role of a small set of PTP proteins in plants. Our current understanding of PTP members in plants may very well be the tip of the proverbial iceberg, but more functional implications of tyrosine phosphorylation will make the picture clear. This chapter presents an updated account of PTP family members in plants, with an emphasis on the functional perspective, especially under stress and physiological responses.