Physiological Characteristics And Transcriptomics Analysis Of Chlamydomonas Reinhardtii Cultured By Green Light

Plants cannot grow without sunlight,which not only regulates plant growth and development as a signal factor,but also provides necessary energy for photosynthesis.Green light is an important component of visible light,and its content is relatively high in the bottom of the canopy and water environment.However,the mechanism of the effect of green light on plant growth and development is not clear.In this study,Chlamydomonas reinhardtii(C.reinhardtii)was used to investigate the effects of green light on plant growth and development.C.reinhardtii also known as "green yeast",is a single-cell green algae that contains a large cup-shaped chloroplast with a volume ratio of about 70%.C.reinhardtii has the characteristics of short growth cycle,fast growth,short generation time,simple molecular genetic background and so on.At present,genome sequencing has been completed,and it is an important model organism for studying the regulation mechanism of photosynthesis.Therefore,in this study,after synchronization,the algae body was converted to green light at different times(0 h,1 h,2 h,4 h,8 h,12 h)as the material.RNA-seq transcriptome sequencing was performed to systematically mine induced genes related to C.reinhardtii light quality conversion.The main research results are as follows:1.Green light significantly affected the growth and photosynthetic physiological and biochemical characteristics of C.reinhardtiiAfter synchronization of C.reinhardtii,the biomass was measured within 12 hours after light quality conversion,and the pigment component content,chlorophyll fluorescence parameters and 77 K low-temperature fluorescence spectrum of the algae at the 12 th hour were also measured.These results showed that the green light samples grown slower than that in the white light at the early stage of light quality conversion,but at the later period,the biomass of the green light samples was similar to that of white light samples.In the green light environment,the pigment composition in C.reinhardtii was altered,and total chlorophyll content、chlorophyll a/chlorophyll b ratio were decreased.However,the neoxanthin content increased.these results suggested that the expression level of LHCII was increased.;The maximum light energy conversion efficiency(Fv/Fm)of photosystem II,the decrease in photochemical quenching capacity(q P)and the relative electron transfer rate r ETR(II)of photosystem II were decreased,indicating the ratio of reactive centers of photosystem II was declined.The analysis of 77 K low-temperature fluorescence spectroscopy showed that the peak positions of photosystem I and photosystem II were not shifted under green light conditions,which were 710 nm and680 nm,respectively,but the ratio of F680/F710 was slightly lower,indcating part of energy absorbed by the light-harvesting antenna II was transferred to the photosystem I.It was possible that the green light might induce the state transition.2.Differentially expressed genes in response to green light were identified and a regulatory network of transcription factors for green light-responsive genes was constructedUsing transcriptome sequencing technology,high-throughput transcriptome sequencing was performed on C.reinhardtii at different times after light quality conversion.After sequencing quality control,at least about 20 million Clean Reads and 3 Gb Clean Data were obtained in each sample.Differential expression analysis showed that,the number of differentially expressed genes of C.reinhardtii gradually decreased along with the increased processing time,indicating that a special mechanism exsited in C.reinhardtii to regulate gene expression for adapting the green light.Through GO enrichment analysis and KEGG enrichment analysis of differentially expressed genes,green light treatment significantly affected the photosynthesis,pigment synthesis,metabolism and other pathways of C.reinhardtii,which was consistent with pigment content and photosynthetic fluorescence characteristics in green light.Furthermore,the ARACNE method was used to construct a complex regulatory network of TF about green light response genes.579pairs(including 326 pathway genes and 17 TFs)can be simultaneously supported by the results of Plant TFDB identification.