Xiutao Sun

Conserved and novel heat stress‐responsive microRNAs were identified by deep sequencing in Saccharina japonica (Laminariales, Phaeophyta)

As a temperate-cold species, Saccharina japonica often suffers heat stress when it is transplanted to temperate and subtropical zones. Study the heat stress response and resistance mechanism of Saccharina is of great significance for understanding the acclimation to heat stress under domestication as well as for breeding new cultivars with heat stress resistance. In this study, we identified a set of heat stress-responsive miRNAs and analysed their regulation during the heat stress response. CO (control) and heat stress (HS) sRNA libraries were constructed and sequenced. Forty-nine known miRNAs and 75 novel miRNAs were identified, of which seven known and 25 novel miRNAs were expressed differentially under heat stress. Quantitative PCR of six selected miRNAs confirmed that these loci were responsive to heat stress. Thirty-nine and 712 genes were predicted to be targeted by the seven known miRNAs and 25 novel miRNAs, respectively. Gene function and pathway analyses showed that these genes probably play important roles in S. japonica heat stress tolerance. The miRNAs identified represent the first set of heat-responsive miRNAs identified from S. japonica, and their identification can help elucidate the heat stress response and resistance mechanisms in S. japonica.

Distribution, function and evolution characterization of microsatellite in Sargassum thunbergii (Fucales, Phaeophyta) transcriptome and their application in marker development.

Using transcriptome data to mine microsatellite and develop markers has growingly become prevalent. However, characterizing the possible function of microsatellite is relatively rare. In this study, we explored microsatellites in the transcriptome of the brown alga Sargassum thunbergii and characterized the frequencies, distribution, function and evolution, and developed primers to validate these microsatellites. Our results showed that Tri-nucleotide is the most abundant, followed by di- and mono-nucleotide. The length of microsatellite was significantly affected by the repeat motif size. The density of microsatellite in the CDS region is significantly lower than that in the UTR region. The annotation of the transcripts containing microsatellite showed that 573 transcripts have GO terms and can be categorized into 42 groups. Pathways enrichment showed that microsatellites were significantly overrepresented in the genes involved in pathways such as Ubiquitin mediated proteolysis, RNA degradation, Spliceosome, etc. Primers flanking 961 microsatellite loci were designed, and among the 30 pairs of primer selected randomly for availability test, 23 were proved to be efficient. These findings provided new insight into the function and evolution of microsatellite in transcriptome, and the identified microsatellite loci within the annotated gene will be useful for developing functional markers in S. thunbergii.

AFLP fingerprints of Pyropia yezoensis (Bangiales, Rhodophyta) populations revealed the important effect of farming protocols on genetic diversity

Abstract Continuous and intensive selective breeding reduces the genetic diversity of cultivated Pyropia stock, thereby increasing its susceptibility to diseases, and hindering the sustainable development of the Pyropia industry. To develop new Pyropia germplasms with desirable agronomic traits, a new Pyropia yezoensis strain, “Huangyou No. 1” was bred from a wild subtidal population. In this study, the genetic diversity of this strain was analyzed using AFLP. Totally, 249 loci were obtained, of which 248 were polymorphic with a polymorphism rate of 99.6%, using seven primer pairs. The intra-population polymorphism rates of the populations Wild 1 and Wild 2 were the highest (47.39% and 59.44%, respectively), while they were relatively low (20.88–24.5%) in the cultivated populations. The genetic distances between the breeding Pyropia populations cultivated in the same aquaculture farm were low. Specifically, the F2 offspring of “Huangyou No. 1” and the control cultivar, cultivated using the “never-drying” protocol, were genetically distant from the other populations, including that from the same seedlings, yet cultivated using the “periodic-drying” protocol. The never-drying cultivation protocol had a high likelihood of influencing genetic diversity of Pyropia yezoensis.

Primary investigations on the photosynthesis and respiration of leaves of Sargassum thunbergii using liquid-phase oxygen measurement system

For clarifying the physiological and ecological adaptability of leaves of Sargassum thunbergii,the photosynthesis and respiration were investigated by using liquid-phase oxygen measurement system.The major results included two aspects:(1) The differences of maximal net photosynthetic rate(Pnmax),saturation irradiance(Isat),light compensation point(Ic),initial quantum yield α,dark respiration rate(Rd),pigment content,specific leaf area and microstructure of heteromorphism leaf(broad leaf,narrow leaf,pneumathode) were analyzed to reveal the probable reason about the change of leaf shape of S.thunbergii.(2) Effects of different temperatures and different salinities stress on Pn and Rd of broad leaves of newborn branch of S.thunbergii were researched.The preliminary analysis of the newborn branch about resistance physiology could provide reference for the artificial cultivation of S.thunbergii based on vegetative reproduction.The results are shown as follows: The optimum temperature for growth of newborn branch is 15-24 ℃ under the experimental conditions in this paper.Pn had significant reduction when temperature was 5 ℃ or higher than 30 ℃ and Rd was significantly affected by low temperature(10 ℃ or below) or high temperature(higher than 30 ℃) stress for one hour treatment.However,Pn or Rd of low temperature stress groups could nearly recover to normal level after 24 h under standard culture condition.Short-term high or low salinity tests,especially salinity 0 and salinity 60 stress,had significant influence on Pn of broad leaves.However,Pn of salinity 0 group could recover to normal level after a 24 h recovery period,but Pn could not recover after exposure to salinity 60 for 9 h.During the whole stress process,Rd of salinity 40 and salinity 50 treatments both showed high values.And salinity 0 and salinity 60 stress both had significant influence on Rd.However,Rd could recover to normal level after a 24 h recovery period after exposure to different salinities for 9 h.