Temporal and stage-specific variation in mite-induced responses of tomato plants

Plants have evolved a rich array of defenses to resist being eaten by herbivores. Spider mites - a group of herbivorous mites - generally induce a combination of JA- and SA- regulated defenses. Solanaceae specialist Tetranychus evansi and some strains of the generalist two-spotted spider mite, Tetranychus urticae were observed to suppress these defenses. This suppression was found to benefit attacking spider mites. In this thesis, I have investigated the robustness of the plant defense induction and suppression framework by introducing more system complexity (mainly variation in abiotic conditions same as in greenhouses and in nature) into the experiments. First, herbivore life stage was found to be a relevant factor when investigating plant responses to spider mites especially for determining which type of defense (i.e., JA or SA) is most relevant for plant resistance. Subsequently, induced SA- and JA-related defenses are subject to diurnal variation possibly causing tomatoes to incur more feeding damage during the dark phase. Mites, especially T. evansi, relax effector production during the dark phase. Further investigation of the effects of a small group of putative secreted effector proteins on plants did not find (direct) evidence that these mite proteins decrease plant palatability via an effect on defenses. The yeast-two-hybrid screens revealed predominantly plant target-proteins associated with different aspects of SA-mediated defenses, the effect of SHOT proteins on defenses may be post-translational. Finally, it was shown that plants have plastic control over reproduction and can speed up fruit and seed production when conditions are unfavorable.