Functional Genomics Center Seminar

 

▶Subject : Transcriptome Analysis of Triacylglycerol Metabolic Pathways in Nitrogen-Deprived Photoautotrophically-Grown Chlamydomonas reinhardtii

▶Speaker : Prof. Heriberto Cerutti(university of nebraska-lincoln)

▶Date : 3:00PM/Sep. 21(Fri)/2012

▶Place : Auditorium(1F), Postech Biotech Center

 

*Abstract
Microalgae are gaining attention as a potential feedstock for the production of biodiesel, mainly derived from triacylglycerols (TAG). In many algae, TAG synthesis increases dramatically upon certain stresses but this is often accompanied by growth retardation. Rational improvements to strain productivity are limited by inadequate knowledge of algal lipid metabolism and gene regulatory mechanisms. In this context, systems-level approaches aimed at understanding and modeling metabolic and regulatory networks may enable hypothesis-driven genetic engineering strategies. The green microalga Chlamydomonas reinhardtii accumulates significant amounts of TAGs under nutrient starvation and provides a genetically tractable model for manipulating lipid biosynthetic pathways. To gain insight into Chlamydomonas TAG metabolism, we have examined the transcriptome of strain CC-125 grown photoautotrophically in nutrient-replete or nitrogen-depleted media. Deep sequencing using RNA-seq technology revealed, under nitrogen starvation, a global decrease in transcript abundance for genes involved in photosynthesis and protein synthesis, whereas many genes related to nitrogen uptake and assimilation were up regulated. We carried out a detailed analysis of the transcriptome focused on genes encoding enzymes for TAG biosynthesis and/or degradation pathways. These components were identified based on orthology relationships to known TAG metabolism enzymes from land plants and fungi. In plants, fatty acids (FA) are mainly synthesized in the plastid by the FASII complex. Free FAs are then exported to the cytosol, converted to acyl-CoA and used predominantly in the ER for TAG synthesis. TAG/FA degradation involves the peroxisome located beta-oxidation pathway. Interestingly, in Chlamydomonas, few genes encoding enzymes in these metabolic pathways showed significant changes in transcript abundance under nitrogen depletion, despite a marked increase in TAG accumulation under these conditions. The expression of most genes involved in FA synthesis or beta-oxidation did not change or showed some reduction. In contrast, several genes putatively involved in the Kennedy pathway of TAG synthesis were up regulated. The greatest increases in transcript abundance corresponded to DGTT1, MLDP and an MBOAT acyltransferase. A few putative transcription factor genes also displayed enhanced mRNA levels under nitrogen depletion and, in clustering analyses, correlated with the increased expression of the TAG synthesis genes. We are now using RNA interference approaches to verify the functional significance of these transcription factors as well as of the lipid biosynthesis enzymes in the TAG accumulation that takes place under nitrogen depletion. These components may represent potential targets for the biotechnological improvement of oil production in microalgae. However, our findings are also consistent with the hypothesis that TAG synthesis in nitrogen-deprived Chlamydomonas reinhardtii occurs without extensive changes in transcript abundance for most genes specifically involved in lipid metabolism. Instead, post-transcriptional regulatory mechanisms and rerouting of carbon fluxes upon nitrogen limitation may be key determinants of TAG accumulation.

 

☎ Inquiry : Prof. Youngsook Lee(279-2296)