Integrative analysis of the hydroxypyruvate reductases revealing their distinct roles in photorespiration of Chlamydomonas

Photorespiration plays an important role in maintaining normal physiological metabolism in higher plants and other oxygenic organisms such as algae. The unicellular eukaryotic organism Chlamydomonas is reported to have a different photorespiration system from that in higher plants, and only two out of nine genes encoding photorespiratory enzymes have been experimentally characterized. Hydroxypyruvate reductase (HPR), which is responsible for the conversion of hydroxypyruvate into glycerate, is poorly understood and not yet explored in Chlamydomonas. To identify the candidate genes encoding hydroxypyruvate reductase in Chlamydomonas (CrHPR) and uncover their elusive functions, we performed sequence comparison, enzyme activity measurement, subcellular localization, and analysis of knockout/knockdown strains. Together we identify five proteins to be good candidates as CrHPRs, all of which are detected with the activity of hydroxypyruvate reductase. CrHPR1, a NADH-dependent enzyme in mitochondria, may function as the major component of photorespiration, and deletion of CrHPR1 causes severe photorespiratory defects. CrHPR2 takes parts in the cytosolic bypass of photorespiration as the compensatory pathway of CrHPR1 for the reduction of hydroxypyruvate. CrHPR4, with NADH as the cofactor, may participate in photorespiration by acting as the chloroplastidial glyoxylate reductase in glycolate-quinone oxidoreductase system. Therefore, our results reveal that the CrHPRs are far more complex than previously recognized, and provide a greatly expanded knowledge base for studies to understand how CrHPRs perform their functions in photorespiration. These will facilitate the genetic engineering for crop improvement by synthetic biology.

Physiological Metabolism and Antioxidant Capacity of Rainbow Trout (Oncorhynchus Mykiss) Fed Diets with Different Lipid Levels

Background: In order to obtain the suitable lipid requirements of rainbow trout (Oncorhynchus mykiss) cultured in the recirculating aquaculture systems (RAS), the effects of dietary lipid levels on fat-related physiological metabolism and antioxidant defenses were investigated. Four isonitrogenous diets containing 45% crude protein with increasing dietary lipid levels of 12%, 15%, 18%, and 21% were fed to 360 fish with initial body weight of 333.25 ± 20.71 g for 77 d. Results: The results showed that a high lipid diet increased lipase and amylase activities in trout livers, whereas a low lipid diet improved lipase and alkaline phosphatase activities in trout intestines. Meanwhile, increased dietary lipid levels elevated low density lipoprotein content and decreased high density lipoprotein, triglyceride, total cholesterol concentrations and the high density lipoprotein/low density lipoprotein ratio in serum. Moreover, increases in superoxide dismutase, glutathione, and malondialdehyde activities were observed in serum with increasing dietary lipid levels, while catalase activity and the catalase/superoxide dismutase ratio decreased. Conclusion: These results indicate that rainbow trout fed diets with low and medium fat levels received adequate fat nutrition and that the diets ensured healthy growth by improving digestive absorption, fat synthesis and transport, and antioxidant levels, and the L12 group had the best growth performance. In conclusion, rainbow trout are healthier when fed diets with approximately 12% lipid levels in RAS.

Molecular Evidence that Lysiphlebia japonica Regulates the Development and Physiological Metabolism of Aphis gossypii

Lysiphlebia japonica Ashmead (Hymenoptera, Braconidae) is an endophagous parasitoid and Aphis gossypii Glover (Hemiptera, Aphididae) is a major pest in cotton. The relationship between insect host-parasitoids and their hosts involves complex physiological, biochemical and genetic interactions. This study examines changes in the development and physiological metabolism of A. gossypii regulated by L. japonica. Our results demonstrated that both the body length and width increased compared to non-parasitized aphids. We detected significantly increases in the developmental period as well as severe reproductive castration following parasitization by L. japonica. We then used proteomics to characterize these biological changes, and when combined with transcriptomes, this analysis demonstrated that the differential expression of mRNA (up or downregulation) captured a maximum of 48.7% of the variations of protein expression. We assigned these proteins to functional categories that included immunity, energy metabolism and transport, lipid metabolism, and reproduction. We then verified the contents of glycogen and 6-phosphate glucose, which demonstrated that these important energy sources were significantly altered following parasitization. These results uncover the effects on A. gossypii following parasitization by L. japonica, additional insight into the mechanisms behind insect-insect parasitism, and a better understanding of host-parasite interactions.