Comparative transcriptome analysis reveals that photosynthesis contributes to drought tolerance of Nostoc flagelliforme (Nostocales, Cyanobacteria)

Nostoc flagelliforme, a photosynthetic cyanobacterium, is well adapted to drought. However, exploration of factors behind this important feature at a molecular level is limited because of inadequate genome data. This study used transcript sequence data of N. flagelliforme and examined its gene expression in response to drought stress on the basis of RNA-Seq. More than 1.4 G clean reads were generated for each sample using the Illumina sequencing platform. A total of 392 and 659 differentially expressed genes were identified, of which 369 and 502 were upregulated and 23 and 157 downregulated after 6- and 48-h dehydration treatments of N. flagelliforme, respectively. Functional analyses demonstrated that the genes involved in photosynthesis as well as those involved in starch and sucrose metabolism were closely related to response to drought stress. The photosynthetic products, sucrose and trehalose, played important roles as osmotic regulators, stress protectants and reactive oxygen species scavengers in response to drought stress in N. flagelliforme. Quantitative real-time reverse-transcriptase polymerase chain reaction analysis, physiological assays and cell ultrastructure observation further confirmed the results from the RNA-Seq. These findings provide novel information about the molecular mechanisms of drought tolerance in N. flagelliforme.