Isolation and characterization of a mutant defective in triacylglycerol accumulation in nitrogen-starved Chlamydomonas reinhardtii

Abstract

Triacylglycerol (TAG), a major source of biodiesel production, accumulates in nitrogen-starved Chlamydomonas reinhardtii. However, the metabolic pathway of starch-to-TAG conversion remains elusive because an enzyme that affects the starch degradation is unknown. Here, we isolated a new class of mutant bgal1, which expressed an overaccumulation of starch granules and defective photosynthetic growth. The bgal1 was a null mutant of a previously uncharacterized β-galactosidase-like gene (Cre02.g119700), which decreased total β-galactosidase activity 40% of the wild type. Upon nitrogen starvation, the bgal1 mutant showed decreased TAG accumulation mainly due to the reduced flux of de novo TAG biosynthesis evidenced by increased unsaturation of fatty acid composition in TAG and reduced TAG accumulation by additional supplementation of acetate to the culture media. Metabolomic analysis of the bgal1 mutant showed significantly reduced levels of metabolites following the hydrolysis of starch and substrates for TAG accumulation, whereas metabolites in TCA cycle were unaffected. Upon nitrogen starvation, while levels of glucose 6-phosphate, fructose 6-phosphate and acetyl-CoA remained lower, most of the other metabolites in glycolysis were increased but those in the TCA cycle were decreased, supporting TAG accumulation. We suggest that BGAL1 may be involved in the degradation of starch, which affects TAG accumulation in nitrogen-starved C. reinhardtii. This article is part of a Special Issue entitled: Plant Lipid Biology edited by Kent D. Chapman and Ivo Feussner.

Coproduction of lipids and extracellular polysaccharides from the novel green alga Parachlorella sp. BX1.5 depending on cultivation conditions

“…Therefore, carbon flow from starch might supply a part of a precursor for synthesizing lipids or EPS. In green alga, Chlamydomonas , starch and lipids also accumulated along the spaces of thylakoid membranes in the cells, and the content profiles appeared to be similar to those seen in the BX1.5 cells [7,33].…”

Membrane Lipid Remodeling in Response to Salinity

“…Recent evidence has shed light on the role of triacylglycerols (TG), in plant stress tolerance. From these studies it was proposed that TG accumulation in vegetative tissues can serve as an energy reservoir under times of stress [131,132,133,134,135,136]. TG are primarily stored in lipid droplets (LD) or plastoglobules (chloroplast localized LD), along with steryl/wax esters.…”

Triacylglycerol Production in the Snow Algae Chlamydomonas nivalis under Different Nutrient Conditions

“…Cells were then cultured in the growth chamber until the day of harvesting. Chlamydomonas reinhardtii cells were grown in the Tris‐Acetate‐Phosphate (TAP) medium with the growth condition as previously described (Hung et al, ). Final concentrations of vitamins added in the TAP medium for culturing C. nivalis were: vitamin B1 (1.2 μg/mL of thiamine hydrochloride, Cat.…”