The Global Transcriptome Of Pyropia Haitanensis Under High-temperature Stress

Pyropia haitanensis is an economically important marine crop in southern China.Over the past several years,continuous high temperature weather under the background of global warming markedly affected the cultivation of P.haitanensis and strongly reduced the seaweed yield.Although several high temperature-tolerance strains of P.haitanensis have been selected,the knowledge of the mechanisms of response to high temperature stress is rather limited so far.In this study,the whole transcriptome of P.haitanensis was sequenced by Solexa technology.Then,the gene expression profilings of P.haitanensis under high temperature(29?)for 0 h,3 h,6 h,12 h,24 h,2 d,4 d and 6 d were analyzed.The main results are as follows:1.High-throughput sequencing was used to analyze the global transcriptome of P.haitanensis.Approximately 643 million 125 bp paired-end reads were generated using an Illumina HiSeq 2000.De novo assembly with paired-end information yielded 34,465 unigenes with an average length of 646.60 bp.Based on sequence similarity searches with known proteins,a total of 24,081(69.69%)genes were identified.And from the database of these unigenes,a lot of heat shock protein genes and antioxidant system-related genes were selected.2.Gene expressions analysis were performed using 16 samples of high temperature resistant strain under different high temperature treatments.These data suggested the response pattern of P.haitanensis under high temperature stress can be divide into 2 time phases with a turning point at 24 h.We concluded the short-term response mechanism to high temperature stress was: high temperature stress ? levels of reactive oxygen species(ROS)increased? cell membrane and nucleic acid were damaged by oxidation ?phosphatidylinositol signal pathway ?DNA repair,DNA degradation,mismatch repair,heat shock protein synthesis,isoprenoid synthesis,structural protein synthesis ? levels of ROS declined and gene expression level recovered.Meanwhile,the metabolic activities and energy metabolisms were inhibited to adapt to high temperature stress.Afterward,the long-term response mechanism to high temperature stress: continued high temperature stress ? increased ROS contents ? damaged proteins ? phosphatidylinositol signal pathway ?TCA cycle,ubiquitin mediated protein degradation,phagocytosis,antioxidant enzyme synthesis?damaged protein were degraded.At the same time,energy metabolism was enhanced to provide more energy for the immune responses.3.By comparing the gene expressions data between high temperature resistant strain with wild strain,we concluded that the molecular response of high temperature resistant train under high temperature stress was more positive than that of the wild strain.Besides,the primary metabolism and secondary metabolism of high temperature resistant strain recovered faster than the wild strains under high temperature stress.The antioxidant system may play a more important role in high temperature resistant strain under the early stage of high temperature stress resistance relative to wild strain.