| Gracilariopsis/Gracilaria lemaneiformis is the ideal material for genetic research and is an important commercial macroalga,which has an annual harvest of over 100,000 tons dry weight in China.It is used for agar extraction and as fodder for abalone.In addition,G.lemaneiformis is also utilized for inhibition of red tides and bioremediation.So far,extensive research on new strains screening,carbon sequestration assessment,transcriptome and genome has been performed in other algae.However,the related information on G.lemaneiformis is still limited at present.As for screening for new strains,rapid completion of its entire life history is undoubtedly an effective way to accelerate the breeding process.To identify the optimal growth conditions for its all life history stages,four factors and each with four levels were tested via an orthogonal experimental design.Results showed that the main factors that influenced carpospore yield were temperature and salinity,and the optimal combination were 20 0C,salinity 35,15 ?mol m-2 s-1 and 8-14 h light/dark(L/D).Variations in salinity,light and temperature had notable effects on tetraspore release with the optimal conditions being 25?,15 ?mol m-2 s-1,salinity 35 and 8-14 h L/D.Temperature variation also had an significant effect on tetraspore and carpospore development.However,the effects of the other factors were not remarkable.The optimal conditions for tetraspore and carpospore development were 25?,45 ?mol m-2 s-1,12/12 h L/D,salinity 25 and 25?,45?mol m-2 s-1,salinity 30,and 12/12 h L/D,respectively.Temperature significantly affected its fertilization success,whereas the other factors had no significant effect(P>0.05).The optimal combination of the fertilization success was 25?,salinity 30,12/12 h L/D and 15-45?mol m-2s-1.Compared with natural condition,the culture time of the entire life history was reduced by about 3-4 months in the lab in the study.Based on the results of optimized cultivation conditions,we have a successful exploration on spore breeding methods in G.lemaneiformis,which will play a very important role for alleviating the current productive problems of its cultivation.In this process,we observed that spore release could last 7-10 days and generate the daily maximum of 5.71 × 105 tetraspores g-1 fresh weight and 1876 carpospores cystocarp-1,which could meet the small-scale cultivation.The spore density markedly affected the entire process of its growth.When the density of mining spores was 10-20 mm-2,seedlings had the highest growth rate and germination rate.Water depth variation had also a significant influence on seedlings growth.When the water depth was 0.5 meters,the growth rate of seedlings was up to 185.53±27.83 ?m/d.The results could provide valuable information for large-scale culture of seedlings and new strains screening.Moreover,a technical system of screening for new strains in G.lemaneiformis was established using spore breeding methods.Through natural selection in the sea and artificial selection in the lab,G.lemaneiformis "ZC" was successfully obtained and has some outstanding economic traits,such as slender frond,a faster growth rate,a higher temperature tolerance,resistance to waves and a higher protein content.Compared with native species,the yield,PE content and total protein content of "ZC"increased by 15%-30%,11%and 12%,respectively."ZC" was extensively cultivated in Jiaozhou Bay of Qingdao,Lidao of Rongcheng,Luoyuan Bay of Lianjiang and Nanri Island of Putian city,which had obtained good results.G.lemaneiformis had the potential to significantly affect carbon absorption and storage in wave-sheltered intertidal reef systems and coastal ecosystems.In this study,we first investigated seasonal variations in biomass,coverage area,and carbon sequestration during low tide from Aug.2011 to Jul.2012 in Zhanshan Bay,Qingdao.The results showed that the standing biomass and coverage area changed significantly with season.However,seasonal variations in carbon content and water content were not obvious,with an average content of 35.1%and 83.64%,respectively.Moreover,carbon sequestration in individual months varied between 0.67 and 47.03 g C·m-2 and had a high enhancement potential.We also investigated and analyzed its cultivation,growth rate,biomass production,and carbon sequestration from mid-October 2011 to mid-June 2012 in Luoyuan Bay.Results showed that its growth rate and carbon sequestration differed significantly between autumn,winter,and spring.The total cultivation duration was about 234 days/year,and the total biomass production reached 9.54 × 106 kg fresh weight.Annual amount of carbon removed by Gracilaria in China was estimated to range from 1836.35 to 4554.98 t,with an annual average of 3623.02 tons.G.lemaneiformis may be an effective carbon sink removing a considerable mass of carbon from the ocean.In the event,its cultivation in the near coast is the main contributor,followed by wildlife resources in the intertidal zoneUsing next-generation sequencing technologies,we conducted a genome survey of G.lemaneiformis.In total,18.70 Gb of filtered sequence data with an estimated genome size of 97 Mb were obtained.The reads were assembled into 160,390 contigs with a N50 length of 3.64 kb,which were further assembled into 125,685 scaffolds with a total length of 81.17 Mb.Genome analysis predicted a G+C content of 48%and 3490 genes with an average transcript length of 1,429 bp.The identified genes had an average coding sequence size of 1,369 bp,exon length of 1,008 bp,1.36 exons per gene and intron length of 191 bp.From the initial assembled scaffold,transposable elements constituted 54.64%of the genome.We also conducted a global transcriptome analysis of G.lemaneiformis.A total of 33,837,454 clean reads were generated from the cDNA library constructed for a mixture RNA of G.lemaneiformis at different conditions.The assembling of the reads yielded 17,985 unigenes with an average length of 1409 bp.The results of sequence similarity searches indicated that of the 17,985 unigenes,25.2%,22.7%,17.4%and 19.3%had significant matches in the Nr,KEGG,KOG,and UniProt databases,respectively.2,064 unigenes annotate were assigned to at least one GO term with 17,463 functional terms,among which 34.4%for biological processes,33.1%for cellular components,and 32.5%for molecular functions.Out of the 4,086 unigenes annotated using bidirectional BLAST,94.6%were assigned to 6 main categories including 289 KEGG pathways.These features provide a basis for elucidating the genetic mechanism of G.lemaneiformis. |
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