The role of a receptor-like protein kinase (At-RLK3) in the perception of chemical activators in Arabidopsis thaliana

Abstract

English: The involvement of a receptor-like protein kinase, At-RLK3 in the response of A. thaliana to four different plant activators was analyzed in this study. The activators were salicylic acid (SA), benzothiadiazole (8TH), acetylsalicylic acid (ASA) and 2,6-dichloroisonicotinic acid (INA). The activation of the defense response was determined measuring both the activity and expression on protein level of β-1,3-glucanases. SA, ASA, 8TH and INA treatments showed an early transient induction of β-1,3-glucanase activity after treatment. On protein level the majority of polypeptides were constitutively expressed in the SA, 8TH, ASA and INA treated plants, indicating that a pool of inactive β -1,3-glucanase proteins already present in the cells, were activated upon treatment. It was only in the SA and 8TH treated plants that newly synthesized polypeptides were visible during the later stages of the time studies. Once the activation of β -1,3-glucanases was established, the possible involvement of At-RLK3 in the activation of plant defense mechanisms by plant activators, was investigated. It was found that At-RLK3 mRNA accumulated rapidly within plants treated with SA, 8TH, ASA and INA. The results indicated a correlation between the onset of SAR in the plant and the expression of the At- RLK3 gene. Hydrogen peroxide acts as an early marker for the activation of defenses. The fact that H202 levels rose after At-RLK3 expression was already induced, led us to suggest that H202 did not act as the primary signal that binds to At-RLK3 but that it acts downstream of At-RLK3. All four treatments did however show the characteristic oxygen burst shortly after application. These results however need to be substantiated by repeating each experiment. In addition to being involved in defense signalling, a role for At-RLK3 in plant development was also suggested. It was found that the transfer of a second At- RLK3 gene to wild-type plants inhibited the expression of the native gene. These lower At-RLK3 levels led to an altered phenotype of the transgenic plant, implicating a possible role for At-RLK3 in the development of the plant. Elevated levels of At-RLK3 in transgenic plants led a higher induction of PR-2 expression after treatment with salicylic acid. A potential application for At-RLK3 in important crops when treated with plant activators could be envisaged.

Afrikaans: Tydens die studie is die betrokkenheid van die reseptorproteïenkinase (At-RLK3) by die respons van Arabidopsis thaliana op bespuiting met verskillende plantaktiveerders bestudeer. Die plantaktiveerders was salisielsuur (SA), bensotiadiasool (BTH), asetielsalisielsuur (ASA) en 2,6-dichloro-isonikotiensuur (INA). Die aktivering van die verdedigingsrespons was bevestig deur beide β- 1,3-glukanase-aktiwiteit en proteïenvlakke te ondersoek. SA, ASA, BTH en INA het almal vroeë kortstondige induksies van β-1,3-glukanase-aktiwiteit getoon. Op proteïenvlak is die meeste β-1,3-glukanasepolipeptiede konstitutief uitgedruk. Dit dui daarop dat behandeling met die plantaktiveerders 'n poel van reeds bestaande onaktiewe β-1,3-glukanase-ensieme waarskynlik geaktiveer het. Dit was alleenlik in die SA- en BTH-behandelings dat nuwe β-1,3- glukanasepolipeptiede tydens die latere fases van die tydstudie gesintetiseer is. Die volgende stap was om te bepaal of At-RLK3 'n rol speel by die herkenning van die verskillende plantaktiveerders. Na behandeling, het al vier aktiveerders die uiting van die At-RLK3-geen geïnduseer. Resultate dui op 'n verband tussen die uiting van At-RLK3 en die aktivering van die sistemiese verworwe weestand (SAR). Waterstofperoksied akkumulasie is 'n vroeë aanduiding van die aktivering van verdediging in plante. Die toediening van al vier aktiveerders het tot In kortstondige toename in H202-vlakke gelei. Die feit dat die vlakke na die induksie van At-RLK3 geenuiting gestyg het, is In aanduiding dat H202 nie direk aan At-RLK3 bind nie. Dit funksioneer waarskynlik stroomaf van At-RLK3. Hierdie resultate sal bevestig moet word deur die herhaling van elke eksperiment. Na die oordraging van 'n tweede kopie van At-RLK3 na Arabidapsis, is gevind dat die transgeniese plante minder At-RLK3 gevorm het. Dit het daarop gedui dat die uiting van die oorspronklike geen deur die oorgedraagde geen gerem is. Die gevolg was dat die transgeniese plante verskeie abnormaliteite getoon het. Dit het impliseer dat At-RLK3 ook moontlike 'n rol in plant ontwikkeling speel. SA-behandeling en die daarop volgende kunsmatige induksie van die oorgedraagde geen, is bevind dat die transgeniese plante 'n hoër uiting van PR-2 getoon het. Die aanwending van At-RLK3 om plantweerstand in belangrike gewasse te verbeter, kan in vooruitsig gestel word.