AbstractsBiology & Animal Science

In order to protect themselves against several biotic and abiotic stresses, plants are equipped with an array of defense mechanisms. Induced defenses and stress responses play a major role in plant disease resistance and are regulated by a network of interconnected signal transduction pathways with the plant hormones ethylene (ET), jasmonic acid (JA) and salicylic acid (SA) as the crucial mediators. These specific hormone-mediated signaling cascades trigger the expression of distinct sets of stress-related genes leading to tolerance or resistance. F-box proteins are important components in mediating stress responses. They act as members of Skp1-Cullin-F-box (SCF) protein complexes, which target substrate proteins for modification and degradation and thereby allow plants to respond rapidly to environmental stress factors. Arabidopsis genome encodes roughly 700 F-box proteins involved in various processes including plant metabolism, hormonal responses as well as responses to environmental stresses. The amount of F-box proteins in plants is significantly higher than in other eukaryotes indicating SCF-dependent ubiquitination to be a major route for selective protein degradation in plants. In this study we screened a group of Arabidopsis F-box T-DNA lines for their tolerance to several abiotic and biotic stresses. To do this, we employed a reverse genetic screening approach and characterized the phenotypes of the T-DNA mutant lines. Among the tested lines, two T-DNA insertion lines with insertions in genes encoding MAX2 and AFB4 demonstrated altered response to ozone and pathogens, respectively, and were therefore chosen for further characterization. In the last part of the thesis, the role of EARLY RESPONSIVE TO DEHYDRATION 15 (ERD15), a negative regulator of abscisic acid responses in Arabidopsis was further characterized concerning its role in biotic stress responses in Arabidopsis. Kasveille on kehittynyt erilaisia tehokkaita puolustusjärjestelmiä, joiden avulla ne suojautuvat muuttuvia, mahdollisesti epäedullisia ympäristöolosuhteita vastaan. Erityisen tärkeässä asemassa on erilaisissa stressitilanteissa indusoituvien puolustusreittien verkosto, jossa signaaleja välittävät erilaiset kasvihormonit kuten etyleeni (ET), jasmonihappo (JA) ja salisyylihappo (SA). Näiden puolustusreittien aktivoituminen tähtää erilaisten spesifisten puolustusproteiinien valmistukseen ja sen myötä kasvin stressinkestävyyden paranemiseen. Kasveissa F-box proteiinit ovat keskeisiä biologisten prosessien säätelijöitä. Ne toimivat osana E3-ligaaseihin kuuluvaa SCF-kompleksia (SKP1-CUL1-F-Box-protein), joka kohdentaa solun proteiineja muokattaviksi ja hajotettaviksi ja mahdollistaa siten kasvin nopean reagoinnin erilaisiin stressitiloihin. Lituruohon (Arabidopsis thaliana) genomista on löydetty noin 700 F-box proteiinia, mikä on selvästi enemmän kuin muista eukaryooteista. Monet jo tunnetut F-box proteiinit osallistuvat erilaisiin kasvin metaboliaan ja hormoni- ja stressisignalointiin liittyviin vasteisiin. Nämä moninaiset roolit korostavat…