The stem parasitic plant Cuscuta gronovii is largely considered to be holoparasitic due to its characteristic yellow stems and total reliance on a host for survival. However, several tissues exhibit greening at various points in C. gronovii’s life cycle, similar to several other Cuscuta species. This greening, as well as the maintenance of key photosynthesis genes, suggests that C. gronovii has more photosynthetic capability than previously expected, and may be using its limited photosynthetic apparatus to drive nutrient accumulation in seeds. In particular, previous research has suggested that the RuBisCO shunt, an alternate pathway utilizing RuBisCO and the energy from photosynthesis to efficiently generate lipids for seed filling, may be active in Cuscuta species. This thesis seeks to evaluate this hypothesis using multiple lines of evidence. Putative orthologs for several pathways of interest—photosynthesis, chlorophyll and lipid synthesis, RuBisCO shunt, and Calvin cycle—were identified in C. gronovii, and their expression across fruit and seedling development was measured using transcriptome data. Stable isotope tracking experiments were used to confirm RuBisCO activity in floral and fruit tissues, and evidence for chlorophyll pigments was found in different green tissues. While the question of the RuBisCO shunt’s activity is still unclear, these experiments provide clear evidence for photosynthetic activity in C. gronovii and open up many avenues for future research.
