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Improving seedless kelp (Saccharina japonica) during its domestication by hybridizing gametophytes and seedling-raising from sporophytes.

ABSTRACT: Dongfang no.7 (Saccharina japonica) was bred and maintained by hybridizing gametophytes, self-crossing the best individuals, selecting the best self-crossing line and seedling-raising from yearly reconstructed sporophytes. It increased the air dry yield by 43.2% in average over 2 widely farmed controls. Dongfang no.7 was seedling-raised from bulked sporophytes reconstructed from its representative gametophyte clones. Such strategy ensured it against variety contamination due to possible cross fertilization and occasional mixing and inbred depletion due to self-crossing number-limited sporophytes year after year. It derived from an intraspecific hybrid through 4 rounds of self-crossing and selection and retained a certain degree of genetic heterozygosity, thus being immune to inbred depletion due to purification of unknown detrimental alleles. Most importantly, it can be farmed in currently available system as the seedlings for large scale culture can be raised from reconstructed Dongfang no.7 sporophytes. Breeding and maintaining Dongfang no.7 provided a model that other varieties of kelp (S. japonica) and brown algae may follow during their domestication.

SUBMITTER: Li X

PROVIDER: S-EPMC4757934 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundBrown macroalgae dominate temperate coastal ecosystems, and their productivity is typically limited by nitrate availability. As an economically important kelp, Saccharina japonica is the most productive farmed seaweed and needs to be supplemented with sufficient nitrate throughout the cultivation process. However, molecular characterization of genes involved in nitrogen assimilation has not been conducted in brown macroalgae.ResultsHere, we described the identification of the nitrate reductase (NR) gene from S. japonica (SjNR). Using two different cloning methods for SjNR, i.e. rapid amplification of cDNA ends (RACE) and cDNA cloning alone, a single fragment was obtained respectively. According to results of sequence analysis between these two fragments, the tentative coding sequence in two clones, SjNR-L and SjNR-S, were suggested to represent two transcripts of the single copy SjNR, and the ATG of SjNR-S was located inside the third exon of SjNR-L. In the 5' upstream sequence of each transcript, promoter core elements, response elements, especially multiple N response elements which occurred in microalgal NR, were all predicted. Further sequence analysis revealed that both transcripts encoded all five domains conserved in eukaryotic plant NRs. RT-qPCR results showed that the transcription level of SjNR in juvenile sporophytes could be significantly induced by nitrate and inhibited by ammonium, which was in line with plant NRs. The recombinant SjNR-L and SjNR-S were all proved to have NR activity, suggesting that the single-copy gene SjNR might be regulated on transcription level based on alternative promoters and multiple transcriptional start sites. Moreover, both NADH and NADPH were found to be able to act as electron donors for SjNR alone, which is the first confirmation that brown algal NR has a NAD(P)H-bispecific form.ConclusionThese results will provide a scientific basis for understanding the N demand of kelp in various stages of cultivation and evaluating the environmental remediation potential of kelp in eutrophic sea areas.

Project description:BACKGROUND:Alginate is an important cell wall component and mannitol is a soluble storage carbon substance in the brown seaweed Saccharina japonica. Their contents vary with kelp developmental periods and harvesting time. Alginate and mannitol regulatory networks and molecular mechanisms are largely unknown. RESULTS:With WGCNA and trend analysis of 20,940 known genes and 4264 new genes produced from transcriptome sequencing of 30 kelp samples from different stages and tissues, we deduced that ribosomal proteins, light harvesting complex proteins and "imm upregulated 3" gene family are closely associated with the meristematic growth and kelp maturity. Moreover, 134 and 6 genes directly involved in the alginate and mannitol metabolism were identified, respectively. Mannose-6-phosphate isomerase (MPI2), phosphomannomutase (PMM1), GDP-mannose 6-dehydrogenase (GMD3) and mannuronate C5-epimerase (MC5E70 and MC5E122) are closely related with the high content of alginate in the distal blade. Mannitol accumulation in the basal blade might be ascribed to high expression of mannitol-1-phosphate dehydrogenase (M1PDH1) and mannitol-1-phosphatase (M1Pase) (in biosynthesis direction) and low expression of mannitol-2-dehydrogenase (M2DH) and Fructokinase (FK) (in degradation direction). Oxidative phosphorylation and photosynthesis provide ATP and NADH for mannitol metabolism whereas glycosylated cycle and tricarboxylic acid (TCA) cycle produce GTP for alginate biosynthesis. RNA/protein synthesis and transportation might affect alginate complex polymerization and secretion processes. Cryptochrome (CRY-DASH), xanthophyll cycle, photosynthesis and carbon fixation influence the production of intermediate metabolite of fructose-6-phosphate, contributing to high content of mannitol in the basal blade. CONCLUSIONS:The network of co-responsive DNA synthesis, repair and proteolysis are presumed to be involved in alginate polymerization and secretion, while upstream light-responsive reactions are important for mannitol accumulation in meristem of kelp. Our transcriptome analysis provides new insights into the transcriptional regulatory networks underlying the biosynthesis of alginate and mannitol during S. japonica developments.

Project description:BackgroundIn brown algae, dioicy is the prevalent sexual system, and phenotypic differences between male and female gametophytes have been found in many dioicous species. Saccharina japonica show remarkable sexual dimorphism in gametophytes before gametogenesis. A higher level of phenotypic differentiation was also found in female and male gametes after gametogenesis. However, the patterns of differential gene expression throughout gametophyte development and how these changes might relate to sex-specific fitness at the gamete stage in S. japonica are not well known.ResultsIn this study, differences in gene expression between male and female gametophytes in different developmental stages were investigated using comparative transcriptome analysis. Among the 20,151 genes expressed in the haploid gametophyte generation, 37.53% were sex-biased. The abundance of sex-biased genes in mature gametophytes was much higher than that in immature gametophytes, and more male-biased than female-biased genes were observed in the mature stage. The predicted functions of most sex-biased genes were closely related to the sex-specific characteristics of gametes, including cell wall biosynthesis, sperm motility, and sperm and egg recognition. In addition, 51 genes were specifically expressed in males in both stages, showing great potential as candidate male sex-determining region (SDR) genes.ConclusionsThis study describes a thorough investigation into differential gene expression between male and female gametophytes in the dioicous kelp S. japonica. A large number of sex-biased genes in mature gametophytes may be associated with the divergence of phenotypic traits and physiological functions between female gametes (eggs) and male gametes (sperm) during sexual differentiation. These genes may mainly come from new sex-biased genes that have recently evolved in the S. japonica lineage. The duplication of sex-biased genes was detected, which may increase the number of sex-biased genes after gametogenesis in S. japonica to some extent. The excess of male-biased genes over female-biased genes in the mature stage may reflect the different levels of sexual selection across sexes. This study deepens our understanding of the regulation of sex development and differentiation in the dioicous kelp S. japonica.

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Improving seedless kelp (Saccharina japonica) during its domestication by hybridizing gametophytes and seedling-raising from sporophytes.

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