Transcriptome profiling of sulfate deprivation responses in two agarophytes Gracilaria changii and Gracilaria salicornia (Rhodophyta)

The cell wall polymer of agarophytes Gracilaria spp. which supplies more than 50 % of world agar is heavily sulfated. Thus, it is important to investigate the effects of sulfate deprivation on the metabolic pathways of these seaweeds. The transcriptomes of two agarophytes G. changii and G. salicornia upon sulfate-deprivation for 5 days under laboratory conditions were profiled. Sulfate deprivation was conducted on seaweeds collected during the rainy and dry seasons. A total of 1,292 and 1,451 differentially expressed genes (DEGs, =1.5-fold) were identified in sulfate-deprivated G. changii during rainy and dry seasons, respectively, compared to their respective untreated samples, whereby 488 of them had similar expression patterns from the two seasons. In G. salicornia, 3,439 and 1,638 DEGs were identified in sulfate-deprivated samples collected during rainy and dry seasons, respectively, compared to their respective untreated samples, with 618 of them having similar expression patterns for the two seasons. Among the annotated DEGs were genes involved in putative agar biosynthesis pathway, sulfur acquisition and assimilation, metabolism of sulfur-containing amino acids, carbon metabolism, photosynthesis, transport systems and oxidative stress. The findings of this study shed light on the sulfate deprivation responses in agarophytes and help to identify candidate genes involved in agar biosynthesis.