Study On The Transcriptome Changes Of Saccharina Japonica Under Blue Light Induction

Light has critical effect on growth and development of plant. In marineenvironments, many photosynthetic stramenopiles utilize blue light to regulate growth,development and organelle movement. Aureochrome (AUREO) is a new type bluelight photoreceptor specific in photosynthetic stramenopiles. Our study is aim tounderstand the blue light responsive physiological pathways and attribute to the kelpseedling nursing and the juvenile sporophyte incubation.High-throughput paired-end RNA-sequencing (RNA-Seq) technology wasapplied to transcriptomes of S. japonica exposed to blue light and darkness,respectively. Comparative analysis of transcriptome was conducted to correlate theeffect of blue light and their relationship with physiological pathways. It yielded70497non-redundant unigenes with an average length of538bp. Annotation withSwissprot, Nr, GO, KEGG, and COG databases showed that25924unigenescompared well (E-value <10-5) with known gene sequences. Based on RPKM values,the11,660(16.5%) differentially expressed unigenes were detected under the bluelight condition, which exhibited7808upregulated and3852downregulated unigenes.It was supposed that S. japonica undergone extensive transcriptome re-orchestrationduring BL exposure. Pathway enrichment analysis revealed that the annotatedchanges were mainly involved in primary metabolism, transcription, proteinprocessing, cellular transport, biogenesis of cellular components, energy storage, lightresponse and DNA repair. Moreover, a total of43unigenes were putative candidategenes of BL photoreceptor, of which28sequences was highly elevated regulated afterthe BL treatment. Besides,34BL-specific responsive genes were either found orconsidered to be involved with the algal circadian rhythm, flavonoid biosynthesis,photoreactivation and photomorphogenesis. Based on homologous cloning and the rapid amplification of cDNA ends(RACE), the full-length cDNA of AUREO from S. japonica (SjAUREO) was isolated.The full length of SjAUREO was characterized by1013bp with an open readingframe of612bp, which encoded a polypeptide of203amino acids. The deducedamino acid sequence of SjAUREO contained one N-terminal basic region/leucinezipper (bZIP) transcription regulation domain and a single light-, oxygen-, orvoltage-sensitive (LOV) domain near the C-terminus. Homologous analysis showedthat SjAUREO shared40%-92%similarities with those of other photosyntheticstramenopiles. Phylogenetic analysis revealed close phylogenetic affinity betweenSjAUREO and AUREO4of brown alga Ectocarpus siliculosus. Quantitative PCR(qPCR) detection revealed that the SjAUREO transcription was markedly increasedunder BL exposure and dramatically up-regulated in the1month juvenile sporophytethan those in the2and3month materials, which indirectly reflected the SjAUREOwas highly associated with the BL-mediated photomorphogenesis during the growthand early development of juvenile sporophytes. In vitro expression and purification ofthe recombinant SjAUREO with Ni2+affinity chromatography showed that onedistinct band existed at~27kDa. The purified SjAUREO recombinant proteinexhibited two absorption peaks at400and460nm after30min BL illumination.