Study of Dandelion (Taraxacum mongolicum Hand.-Mazz.) Salt Response and Caffeic Acid Metabolism under Saline Stress by Transcriptome Analysis.

Utilizing salt-tolerant plants is a cost-effective strategy for agricultural production on salinized land. However, little is known about the mechanism of dandelion (Taraxacum mongolicum Hand.-Mazz.) in response to saline stress and caffeic acid biosynthesis. We investigated the morphological and physiological variations of two dandelions, namely, "BINPU2" (dandelion A) and "TANGHAI" (dandelion B) under gradient NaCl concentrations (0, 0.3%, 0.5%, 0.7%, and 0.9%), and analyzed potential mechanisms through a comparison analysis of transcriptomes in the two dandelions. Dandelion A had a high leaf weight; high ρ-coumaric acid, caffeic acid, ferulic acid, and caffeoyl shikimic acid contents; and high activities of POD and Pro. The maximum content of four kinds of phenolic acids mostly occurred in the 0.7% NaCl treatment. In this saline treatment, 2468 and 3238 differentially expressed genes (DEGs) in dandelion A and B were found, of which 1456 and 1369 DEGs in the two dandelions, respectively, showed up-regulation, indicating that more up-regulated DEGs in dandelion A may cause its high salt tolerance. Further, Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that dandelion salt response and caffeic acid metabolism were mainly enriched in the phenylpropanoid biosynthesis pathway (ko00940) and response to ethylene (GO: 0009723). The caffeic acid biosynthesis pathway was reconstructed based on DEGs which were annotated to PAL, C4H, 4CL, HCT, C3'H, and CSE. Most of these genes showed a down-regulated mode, except for parts of DEGs of 4CL (TbA05G077650 and TbA07G073600), HCT (TbA03G009110, TbA03G009080, and novel.16880), and COMT (novel.13839). In addition, more up-regulated transcription factors (TFs) of ethylene TFs in dandelion A were found, but the TFs of ERF104, CEJ1, and ERF3 in the two dandelions under saline stress showed an opposite expression pattern. These up-regulated genes could enhance dandelion salt tolerance, and down-regulated DEGs in the caffeic acid biosynthesis pathway, especially CSE (TbA08G014310) and COMT (TbA04G07330), could be important candidate genes in the synthesis of caffeic acid under saline stress. The above findings revealed the potential mechanisms of salt response and caffeic acid metabolism in dandelion under saline stress, and provide references for salt-tolerant plant breeding and cultivation on saline-alkali land in the future.

Continuous biomass and lipid production from local chlorella-bacteria consortium in raw wastewater using volatile fatty acids.

OBJECTIVES: To evaluate mixotrophic cultivation of microalgae-bacteria consortium in raw wastewater by stepwise addition of fermented effluent containing volatile fatty acids (VFAs). RESULTS: Stepwise increase of VFAs enhanced algal biomass and lipid production, ammonia and phosphate removals. The highest biomass and lipid yield were 1.94 g L-1 and 310 mg L-1 when the addition of fermented effluent containing VFAs increased to 30% (v/v). With the same cultivation conditions, the maximum removals efficiency of ammonia and phosphate were 26.4 and 11.3 mg L-1 d-1. Bacterial diversities increased with the increasing concentration of VFAs and their communities were identified as phyla Actinobacteria, Bacteroidetes, Cyanobacteria and Proteobacteria. CONCLUSIONS: Although bacterial quantities increased with algae growth concurrently, the objective of culturing microalgae-bacteria consortium in raw wastewater without sterilization to produce biomass and lipid yield still can be realized.