Characterization of At-RLK3, a putative receptor-like protein kinase from Arabidopsis thaliana

English: An attempt was made during this study to assign a putative role for At-RLK3 in Arabidopsis thaliana. Receptor-like protein kinases (RLKs) are a group of proteins that was described in various plants. These proteins have a very characteristic structure. They are integral plasma membrane proteins where a hydrophobic transmembrane domain links an extracellular ligand binding domain with an intracellular protein kinase domain. RLKs are involved in various plant processes including development, disease resistance and hormonal signaling. At-RLK3 is a single copy gene in A. thaliana that is expressed during various stress conditions. Oxidative and osmotic stress, infection with pathogens and exposure to salicylic acid (SA) all led to the induced expression of the gene. A similar increase in At-RLK3 protein levels was found after the respective treatments. The kinase domain shares high homology with several other protein kinases and has all 11 conserved sub-domains characteristic of plant protein kinases. It was proven that At-RLK3 is an active protein kinase that specifically phosphorylates serine and threonine amino acids within its active domain. It preferentially uses Mg 2+ as cofactor. The enzyme is located at the plasma membrane and is rapidly activated upon treatment with hydrogen peroxide (H2O2), menadione and osmotic stress conditions, but not after SA treatment. The extracellular domain has two conserved cysteine rich regions that form part of two “domain of unknown function” (DUF) regions. These cysteines are thought to be involved in the formation of disulphide bridges and to be responsive to changes in the redox conditions surrounding the cell. Plants expressing an antisense copy of the gene showed an altered response to treatments with H2O2 and SA compared to the wild type plants. Whereas the wild type plants activated the plant defense shortly after treatment with both H2O2 and SA, only SA managed a similar activation in the transgenic plants. The tr
Afrikaans: Die doel van die studie was om ‘n moontlike funksie vir At-RLK3 in Arabidopsis thaliana voor te stel. Reseptorproteïenkinases (RLKs) is ‘n groep proteïene wat in verskillende plante beskryf is. Die proteïene vorm die groep as gevolg van hulle kenmerkende struktuur. Hulle is integrale plasmamembraanproteïene wat in die membraan deur ‘n hidrofobiese transmembraan domein geanker is. Die domein verbind twee ander gedeeltes van die proteïen met mekaar, naamlik ‘n intrasellulêre proteïen kinase domein en ‘n ekstrasellulêre domein wat in staat is om ligande te bind. RLKs is betrokke by ‘n verskeidenheid van sellulêre prosesse soos plantontwikkeling, die weerstand van die plant teen siektes en die oordrag van hormonale seine. At-RLK3 is ‘n enkelkopie geen in die A. thaliana genoom. Die uiting van die geen word deur ‘n verskeidenheid faktore aangeskakel. Dit sluit in oksidatiewe en osmotiese strestoestande, infeksies deur patogene en die blootstelling van die plant aan salisielsuur (SA). Die aktivering van geenuiting was gevolg deur ‘n soortgelyke toename in proteïenkonsentrasie binne die sel. Die kinasedomein toon homologie met verskeie ander plant proteïenkinases. Verder is al 11 gekonserveerde subdomeins wat kenmerkend is van aktiewe proteïen kinases, teenwoordig. At-RLK3 is ‘n aktiewe proteïenkinase wat serien en treonien aminosure in sy kinasedomein spesifiek fosforileer. Die ensiem gebruik ook by voorkeur Mg2+ as kofaktor. Die ensiem is plasmamembraan gebonde en word vinnig na waterstofperoksied (H2O2), menadioon en osmotiese stres behandelings geaktiveer. SA behandeling aktiveer die ensiem egter glad nie. Die ekstrasellulêre domein van At-RLK3 besit twee gekonserveerde sisteïenryke gebiede wat deel vorm van twee ander gebiede wat bekend staan as “domein met onbekende funksie” (DUFs). Dit is moontlik dat die gekonserveerde sisteïene by die vorming van disulfiedbrûe betrokke kan wees en dat dit verder sensitief vir enige veranderings in die redokstoestande bu