PK12, a Plant Dual-Specificity Protein Kinase of the LAMMER Family, Is Regulated by the Hormone Ethylene

Abstract

The ethylene signal is transduced in plant cells via phosphorylation events. To identify protein kinases whose levels of expression are modulated by the plant hormone ethylene, we utilized a differential reverse transcriptase-polymerase chain reaction approach using mRNA extracted from ethylene-treated and untreated tobacco leaves. An ethylene-induced cDNA clone, PK12, encoding a protein kinase, was isolated. PK12 is a new member of the recently defined LAMMER family of protein kinases, which has been identified in mammals, flies, yeasts, and plants. The LAMMER kinases are related to the cell cycle-dependent CDC2-type kinases and are characterized by their similarity at kinase subdomain X. The recombinant PK12 protein autophosphorylates in vitro on serine, threonine, and tyrosine residues, thereby making it a member of the dual-specificity protein kinases. Immunoprecipitation of PK12 from plant extracts and kinase assay revealed that the apparent PK12 activity is rapidly and transiently increased when plants are treated with ethylene. By using in situ hybridization, we detected accumulation of the PK12 transcript in leaves after ethylene treatment and in the untreated flower abscission zone. The tissue in this zone is known to constitutively express ethylene-regulated genes.

The CLK Family Kinases, CLK1 and CLK2, Phosphorylate and Activate the Tyrosine Phosphatase, PTP-1B

“…2 Similarly, staining of endogenous CLK1 in PC12 cells found it to be mostly cytoplasmic as well. In agreement with a putative signaling role for the CLK kinases is the finding that ethylene stimulation of tobacco leaves stimulates the activity of the tobacco CLK family member, PK12 (24). These finding strongly suggest the existence of cytoplasmic targets for the CLK family kinases and their participation in intracellular signaling pathways.…”

Characterization of a dual plant protein kinase (FsPK1) up-regulated by abscisic acid and calcium and specifically expressed in dormant seeds ofFagus sylvaticaL.

“…Further molecular confirmation of the kinase activity, using other substrates and performing autophosphorylation assays, is under investigation. There are not many plant protein kinases with both activities described so far, and just a few of them, such as ADK1 from Arabidopsis thaliana (Ali et al, 1994), or PK12 (Sessa et al, 1996) and NtDSK1 (Cho et al, 2001) from tobacco, have been confirmed to have dual specificity in vitro. FsPK1 would be the first dual plant PK induced by ABA.…”

A novel dual‐specificity protein kinase targeted to the chloroplast in tobacco1

“…Dual‐specificity protein kinases are a group of protein kinases which are able to phosphorylate both tyrosine and serine/threonine residues [1]. In plants, characterization of dual‐specificity protein kinases that do not belong to the MAP kinase kinase family is restricted to ADK1 from Arabidopsis [2], PRK1 from petunia [3], and PK12 from tobacco [4]. PRK1 is a predominantly pollen‐expressed receptor‐like kinase which autophosphorylates on serine and tyrosine [3].…”

“…PK12 is a member of the LAMMER kinases. PK12 activity is rapidly and transiently increased when plants are treated with ethylene [4]. The PK12 kinase phosphorylates serine/arginine‐rich (SR) splicing factors in vivo to alter their activity and the splicing of target mRNAs [7].…”