Chapter 11 - Thaumatin-domain containing receptor-like kinases in plants

Abstract

Thaumatin-like proteins (TLPs) are a large and composite family, which falls under the pathogenesis-related 5 (PR5) superfamily. These are multifunctional proteins, induces in response to various abiotic and biotic stresses. TLPs are also involved in plant growth and development. TLP family also has thaumatin-like protein kinases (TLPKs), which are fusion products of thaumatin and kinase proteins. TLPK was firstly evidenced in the Arabidopsis thaliana and named PR5K. Till now, these genes were identified in a number of plant species, for instance, A. thaliana, Brachypodium distachyon, Hordeum vulgare, O. sativa, Populus trichocarpa, and Triticum aestivum. Evolutionary analyses show the divergence of TLPKs from usual TLPs up to some extent. Moreover, purifying selection pressure was reported as the major contributing factor in the expansion of the TLPK gene family. Structurally, TLPKs are identical to typical RLKs having N- a terminal extracellular domain, membrane-spanning hydrophobic domain, and a C-terminal kinase domain. The alteration in various residues of the thaumatin domain is responsible for the interaction of TLPKs with diverse elicitors. Like usual TLPs, these proteins also have various conserved regions, such as a thaumatin-signature motif, 16 conserved cysteine residues, REDDD motif, acidic cleft, FF hydrophobic motif, and conserved aspartic acid residues. Functional aspect-based studies of TLPKs revealed their plausible role in physiological, biochemical, and reproductive processes. Furthermore, the studies based on expression profiling, knockout approach, and overexpression methods established their participation in a variety of biotic and abiotic stress conditions.