Research On Molecular Response Mechanism Of Intertidal Macroalgae Under Enhanced UV-B Radiation

Due to human activities,natural factors,and the development of the industrial and agricultural production,the environment has been greatly damaged and affected.The weakening of the ozone layer in the stratosphere has led to the increase of ultraviolet radiation reaching the earth's surface as one of the most significant global environmental problems.Intertidal zone is the interlaced zone of terrestrial ecosystem and marine ecosystem,and it is one of the most sensitive ecosystems in the biosphere.Large seaweeds living in the intertidal zone are subject to the light radiation environment with the largest fluctuation range.Especially at low tides,dried large seaweeds are bound to be exposed to full light conditions.Therefore,the direct harm of UV-B radiation will be more serious than when submerged.So far,with regard to the effects of UV-B radiation on intertidal macroalgae,research has focused on the effects of UV radiation on the growth,respiration,DNA damage,and single antioxidant enzyme activity of algae.However,there is still no systematic research on the molecular response mechanism of the large intertidalalgae response to UV-B radiation enhancement.Therefore,in this study,the large intertidal seaweed Ulva pertusa and Sargassum thunbergii in Yantai seashore were selected as test materials.By measuring chlorophyll content and chlorophyll fluorescence parameters,the change trend of photosynthetic physiological characteristics of seaweed under UV-B exposure was studied.Using two-dimensional electrophoresis technology to analyze soluble protein species and expression intensity of algae under UV-B treatment,and to further clarify the correlation ship of UV-B stress factors and protein expression trends.Using RNA-seq library sequencing to study changes in transcription information of algae,and further explore the molecular biological response mechanism of U.pertusa and S.thunbergii to enhanced UV-B radiation.The results are as follows:(1)Response of chlorophyll content and chlorophyll fluorescence parameters to UV-BradiationChlorophyll is the basic material for photosynthesis of plants.Determination of chlorophyll content is an important indicator of plant growth.With the increase of UV-B radiation,the content of photosynthetic pigments in U.pertusa was significantly decreased.Significant analysis showed that there were extremely significant differences between Chl.a,Chl.b and Car compared with the control group(P<0.01).Chlorophyll fluorescence parameters are a set of variables or constants used to describe the photosynthetic physiology and photosynthetic mechanism of plants.They can reflect the intrinsic characteristics of plants and can therefore study the relationship between plant photosynthesis and the environment.In this study,the maximum photochemical efficiency Fv/Fm of both U.pertusa and S.thunbergii showed a significant decrease compared with that of the CK group,and it decreased to the lowest value on the fifth day of treatment(P<0.01);non-photochemical quenching coefficient NPQ values gradually increased with increasing UV-B stress levels,but the increase range was different.The increase of NPQ value of U.pertusa was slightly higher than that of S.thunbergii.The photochemical quenching coefficient(qp)of U.pertusa under UV-B treatment always showed a general trend of decrease(P<0.01),but the value of U.pertusa appeared to decrease first and then rise.The maximum utilization efficiency alpha of U.pertusa reached extremely significant fifference on the 3d day(P < 0.01),while that of S.thunbergii reached extremely significant difference on the fifth day compared with the control(P < 0.01).(2)The response of protein expression in the algae of U.pertusa and S.thunbergii to UV-B radiationTwo-dimensional electrophoresis analysis showed that the enhanced UV-B radiation resulted in the inhibition of protein expression in both U.pertusa and S.thunbergii,and the total number of proteins showed a decreasing trend.By PDQuest software analysis,the protein spots of U.pertusa were mainly concentrated between the molecular mass of 14-30 kD,and the isoelectric point distribution between,8 to 9had the highest percentage.The protein spots of S.thunbergii were mainlyconcentrated between the molecular weight of 15-30 kD and the isoelectric point of0-5 had the largest number.The difference between the control and UV-B treatments was mainly embodied as protein abundance and protein type changes.(3)The response of gene expression to UV-B radiation in the algae of U.pertusa and S.thunbergiiThe results of RNA-seq analysis showed that the expression of immune response genes,immune system progression genes,viral response genes,and apoptosis-regulatory genes were up-regulated under UV-B irradiation.Among them,immune response genes were most abundant in differentially expressed genes(DEGs).However,under UV-B irradiation of S.thunbergii,expression genes involved in the regulation of developmental processes,immune processes,multicellular tissue processes,regeneration processes,and signal transduction processes were all down-regulated.KEGG analysis showed that most of the DEGs in pseudopadus konjac were enriched in the ribosome,metabolism and other pathways;the DEGs of S.thunbergii were enriched in RNA transcription,endoplasmic reticulum protein modification,ribosome,phagosome and other pathways,which were enriched in phagosome and endoplasmic reticulum protein modification.The most genes are in the process.