Chlorella sp. TLD 6B, a microalgae growing in the Taklamakan Desert, Xinjiang of China, is a good model material for studying the physiological and environmental adaptation mechanisms of plants in their arid habitats, as its adaptation to the harsh desert environment has led to its strong resistance. However, when using real-time quantitative polymerase chain reaction (RT-qPCR) to analyze the gene expression of this algae under abiotic stress, it is essential to find the suitable endogenous reference genes so to obtain reliable results. This study assessed the expression stability of 9 endogenous reference genes of Chlorella sp. TLD 6B under four abiotic stresses (drought, salt, cold and heat). These genes were selected based on the analysis results calculated by the three algorithmic procedures of geNorm, NormFinder, and BestKeeper, which were ranked by refinder. Our research showed that 18S and GTP under drought stress, 18S and IDH under salt stress, CYP and 18S under cold stress, GTP and IDH under heat stress were the most stable endogenous reference genes. Moreover, UBC and 18S were the most suitable endogenous reference gene combinations for all samples. In contrast, GAPDH and α-TUB were the two least stable endogenous reference genes in all experimental samples. Additionally, the selected genes have been verified to be durable and reliable by detecting POD and PXG3 genes using above endogenous reference genes. The identification of reliable endogenous reference genes guarantees more accurate RT-qPCR quantification for Chlorella sp. TLD 6B, facilitating functional genomics studies of deserts Chlorella as well as the mining of resistance genes.

The saline, alkaline environment of arid soils is conducive to the diffusion of the metalloid arsenic (As). Desert plants in this area are of great ecological importance and practical value. However, there are few studies on the mechanism of arsenic action in desert plants. Therefore, in this study, Eremostachys moluccelloides Bunge was treated with different concentrations of As₂O₅ [As(V)] to analyze the physiological, biochemical, and transcriptomic changes of its roots and leaves and to explore the molecular mechanism of its response to As(Ⅴ) stress. The activities of catalase, superoxidase, peroxidase, and the contents of malondialdehyde and proline in roots and leaves first increased and then decreased under the As(Ⅴ) stress of different concentrations. The content of As was higher in roots than in leaves, and the As content was positively correlated with As(Ⅴ) stress concentration. In the differentially expressed gene analysis, the key enzymes of the oxidative stress response in roots and leaves were significantly enriched in the GO classification. In the KEGG pathway, genes related to the abscisic acid signal transduction pathway were co-enriched and up-regulated in roots and leaves. The related genes in the phenylpropanoid biosynthesis pathway were significantly enriched and down-regulated only in roots. In addition, the transcription factors NAC, HB-HD-ZIP, and NF-Y were up-regulated in roots and leaves. These results suggest that the higher the As(V) stress concentration, the more As is taken up by roots and leaves of E. molucelloides Bunge. In addition to causing greater oxidative damage, this may interfere with the production of secondary metabolites. Moreover, it may improve As(V) tolerance by regulating abscisic acid and transcription factors. The results will deepen our understanding of the molecular mechanism of As(Ⅴ) response in E. moluccelloides Bunge, lay the foundation for developing and applying desert plants, and provide new ideas for the phytoremediation of As pollution in arid areas.

Microalgae endemic to desert ecosystems possess exceptional stress-resistance traits; however, the physiological and molecular drought-adaptation mechanisms of desert-dwelling Chlorella remain largely uncharacterized. Herein, we combined physiological–biochemical assays, ultrastructural observation, transcriptomics and metabolomics to dissect drought responses in Taklamakan-desert-origin Chlorella sp. under polyethylene glycol 6000 (PEG-6000)-simulated mild (10%), moderate (20%), and severe (30%) drought stress, with mechanistic focus on moderate-drought conditions. Moderate drought repressed algal biomass (−26.32%), chlorophyll a (−24.40%), maximum photosystem II quantum yield (Fv/Fm, −16.55%) and effective quantum yield of photosystem II (ΦPSII, −24.35%). Malondialdehyde (MDA) accumulated (+50.69%), alongside elevated activities of superoxide dismutase (SOD, +156.74%) and catalase (CAT, +11.61%). Compatible solutes, including proline, soluble sugars, total protein and total lipid, increased significantly by 39.00%, 39.36%, 26.35% and 23.06%, respectively (p < 0.05). Moderate drought triggered cell swelling, partial cell-wall rupture and prominent enlargement of intracellular starch granules and lipid droplets. Transcriptomic profiling demonstrated up-regulation of transcription–translation and DNA-repair machinery, ATP-binding cassette (ABC) transporters, abscisic acid (ABA)/jasmonic acid (JA) signaling, and biosynthetic pathways for protective metabolites, whereas catabolic pathways and mitogen-activated protein kinase (MAPK) signaling were suppressed. Untargeted metabolomics further validated accumulation of trehalose, stress-protective amino acids, vitamins and functional lipids, while chloroplast-membrane-related metabolites and catabolic intermediates declined. This multi-omics study systematically reveals physiological and molecular regulatory cascades underlying drought tolerance in desert Chlorella sp., providing candidate genes and metabolites to support microalgal resource exploitation for arid-zone applications.

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.