Desert Chlorella Malate Synthase 1 Enhances Salt Tolerance by Promoting Soluble Sugar and Lipid Accumulation

Desert microalgae possess a remarkable tolerance to extreme abiotic stresses; however, the molecular mechanism underlying their stress adaptation and metabolite accumulation remains poorly understood. In the present study, desert Chlorella sp. TLD 6B was exposed to different concentrations of NaCl to assess changes in the soluble sugar and lipid content, as well as transcriptome profiles. The regulatory role of malate synthase 1 (MS1) in modulating soluble sugar and lipid accumulation was further investigated in desert Chlorella under salinity conditions. The results revealed that salt stress markedly elevated soluble sugar and lipid levels in desert Chlorella, while strongly upregulating the transcript expression and enzymatic activity of MS1. Under salt stress, the overexpression of MS1 in desert Chlorella increased the soluble sugar content by 46.49% and the lipid content by 43.87%. The ectopic overexpression of desert Chlorella MS1 in Arabidopsis enhanced salt and drought tolerance without impacting normal plant growth. Mechanistically, MS1 activation modulates metabolic fluxes of the glyoxylate cycle (GAC) and TCA, thereby promoting soluble sugar and lipid accumulation in Chlorella. These findings advance the understanding of GAC-governed sugar and lipid accumulation in desert Chlorella under salt stress, laying a theoretical foundation for the exploitation of desert microalgae resources in biomass energy development.