Evidence for Serine/Threonine and Histidine Kinase Activity in the Tobacco Ethylene Receptor Protein NTHK2

Abstract

Ethylene plays important roles in plant growth, development, and stress responses. Two ethylene receptors, ETR1 from Arabidopsis and NTHK1 from tobacco (Nicotiana tabacum), have been found to have His kinase (HK) activity and Ser/Thr kinase activity, respectively, although both show similarity to bacterial two-component HK. Here, we report the characterization of another ethylene receptor homolog gene, NTHK2, from tobacco. This gene also encodes a HK-like protein and is induced by dehydration and CaCl 2 but not significantly affected by NaCl and abscisic acid treatments. The biochemical properties of the yeast (Schizosaccharomyces pombe)-expressed NTHK2 domains were further characterized. We found that NTHK2 possessed Ser/Thr kinase activity in the presence of Mn 21 and had HK activity in the presence of Ca 21. Several lines of evidence supported this conclusion, including hydrolytic stability, phosphoamino acid analysis, mutation, deletion, and substrate analysis. These properties have implications in elucidation of the complexity of the ethylene signal transduction pathway and understanding of ethylene functions in plants.Ethylene plays important roles in multiple aspects of plant growth, development, and stress responses (Abeles et al., 1992). In the presence of ethylene, plant seedlings exhibit triple responses in the dark, including inhibited root and hypocotyl elongation, radial expansion of the hypocotyl, and exaggerated growth of the apical hook. Taking advantage of the triple responses, a number of Arabidopsis mutants were genetically screened, and a series of components have been identified to be involved in the ethylene signal transduction pathway (Bleecker and Kende, 2000;Schaller and Kieber, 2002;Wang et al., 2002;Guo and Ecker, 2004). These components include ethylene receptors (Chang et al., 1993;Hua et al., 1995Sakai et al., 1998), the Raf-like Ser/Thr kinase (STK) CTR1 (Kieber et al., 1993), the membrane protein EIN2 (Alonso et al., 1999), and transcription factors EIN3 and ERF family (Chao et al., 1997;Solano et al., 1998). Additional components in the ethylene-response pathway have been found (Alonso et al., 2003), and an alternative pathway has also been suggested (Moshkov et al., 2003).In Arabidopsis, five ethylene receptor genes, namely ETR1, ERS1, ETR2, EIN4, and ERS2, have been isolated, and all of the encoded proteins show similarity to bacterial two-component His kinases (HK;Chang et al., 1993;Hua et al., 1995Sakai et al., 1998). The two-component signal transduction systems allow bacteria to adapt to changing environmental conditions. Based on the amino acid sequence similarity and structural features, the five Arabidopsis ethylene receptors can be classified into two subfamilies (Bleecker and Kende, 2000;Schaller and Kieber, 2002;Wang et al., 2002). Subfamily I contains ETR1 and ERS1, both of which have three transmembrane domains. Subfamily II contains ETR2, EIN4, and ERS2, and all the three proteins have a putative signal peptide in addition to the three conserved transmembrane doma...

REVERSION-TO-ETHYLENE SENSITIVITY1 , a conserved gene that regulates ethylene receptor function in Arabidopsis

“…The membrane-bound Nterminal portion of ETR1 binds ethylene (16) with a copper cofactor Cu(I) (17), but the mechanism of ethylene receptor signaling is unclear. Although ETR1 has histidine autokinase activity in vitro (18), such activity is not required for ethylene signaling in vivo (19)(20)(21), and other ethylene receptors have serine͞threonine kinase activity (21)(22)(23). The ethylene receptors interact with the Raf-like protein kinase CTR1 (24,25), which is a negative regulator of the pathway (26).…”

In silico analysis of ESTs from roots of Rangpur lime (Citrus limonia Osbeck) under water stress

“…Phosphorylations promoted by diverse families of kinases are normally switches of important biochemical processes. Kinases that can be turned on and off under processes related to water stress are known (Zhang et al, 2004), and therefore, a putative kinase was expected to be seen in our results. However, a valuable question considering its potential insertion and contribution in different signaling pathways and different rootstock.…”

Tobacco Translationally Controlled Tumor Protein Interacts with Ethylene Receptor Tobacco Histidine Kinase1 and Enhances Plant Growth through Promotion of Cell Proliferation

“…All of these data imply that plant TCTPs may evolve divergently from animals and have different functions. There are several ethylene receptors in tobacco, among which NTHK1 and NTHK2 belong to subfamily II receptors, and NtETR1 is a subfamily I receptor (Xie et al, 2003;Zhang et al, 2004;Chen et al, 2009). To test the interactions between NtTCTP and different ethylene receptors, the coding regions of these receptors without transmembrane domains were cloned into pSos vector and cotransformed, respectively, with the prey pMyrNtTCTP plasmid into yeast cdc25H cells.…”