Date of Graduation

12-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Entomology (PhD)

Degree Level

Graduate

Department

Entomology

Advisor/Mentor

Fiona L. Goggin

Committee Member

Robert Wiedenmann

Second Committee Member

Donn Johnson

Third Committee Member

Vibha Srivastava

Fourth Committee Member

Kenneth Korth

Keywords

Aphid resistance, chloroplast, enzyme, FAD7, Fatty acid desaturation, glutamate, Photosynthesis, spr2

Abstract

Fatty Acid Desaturase7 (FAD7) is a chloroplast-localized enzyme that converts 16 and 18 carbon dienoic fatty acids to trienoic fatty acids. The suppressor of prosystemin-mediated response2 (spr2) mutant in tomato (Solanum lycopersicum) and the fad7-1 mutant in Arabidopsis (Arabidopsis thaliana) result in the loss of function of FAD7, which alter the fatty acid profiles of chloroplast membranes and enhance resistance against aphids. This research contributes toward the long-term goal of identifying factors that determine aphid resistance in FAD7 mutants. Previous data suggested constitutive differences between spr2 and WT including increased expression of genes associated with photosynthesis and differences in redox status in chloroplasts suggested by lipid profiles. The objective of this study was to validate these previous data. This study reports that the spr2 mutant enhances photosynthetic efficiency constitutively compared to wild-type (WT) plants. While no constitutive differences in intermediates and products of photosynthesis were detected, the spr2 mutants showed increased growth, suggesting increased photosynthesis may be translated in to growth. Moreover, glutamate levels were constitutively higher in spr2 compared to WT and could be important in defense signaling for aphid resistance. Also, the spr2 mutants were able to maintain the enhanced photosynthesis under potato aphid (Macrosiphum lycopersicum) pressure. One-day after aphid infestation, aphids triggered a short-term increase in the energy directed towards photosynthesis. The enhanced photosynthesis could also be channeling energy towards defense compound production for the resistance mechanism or could be the plant adapting to adverse environmental stress, indicative of tolerance. Furthermore, to study the redox status in chloroplasts, Arabidopsis fad7-1 lines containing roGFP2 transgene were developed as a useful tool. Preliminary results indicated the fad7-1 mutant is as or more reduced than WT (Col-0), but further studies are needed to confirm this. The redox status depends on the relative balance between reactive oxygen species (ROS) and antioxidants. The plants could potentially have more ROS due to enhanced photosynthesis, but they could also have more antioxidants. Further work is necessary to detect individual ROS species. This study aids in identifying potential links between primary metabolism and plant defenses against insects.

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