Triacylglycerol synthesis in microalgae under abiotic stress: an updated integrative review

Microalgae exhibit remarkable metabolic plasticity, rapidly redirecting carbon toward triacylglycerol (TAG) accumulation under environmental stress. In this review, we synthesize recent advances in understanding how nutrient limitation, light fluctuations, salinity, temperature extremes, and chemical modulators regulate TAG biosynthesis in diverse microalgal systems. Under stress, TAG accumulation is typically linked to the coordinated transcriptional and metabolic reprogramming of the glycerol-3-phosphate (Kennedy) pathway, with diacylglycerol acyltransferases acting as the pivotal enzymes that complete TAG biosynthesis. However, these responses are highly species- and isoform-specific, reflecting substantial evolutionary divergence. In addition to enzyme-level control, increasing evidence points to a central role for intracellular signaling networks and transcription factors in coordinating these responses. Although upstream regulatory mechanisms differ, their outcomes commonly result in enhanced TAG accumulation and the remodeling of fatty acid pools. Together, these findings support a hierarchical model in which environmental sensing, signal integration, and transcriptional regulation coordinate TAG biosynthesis as an adaptive response to environmental stressors.