Transcriptome Of Medicago Sativa L. And Medicago Falcata L. Under Drought Stress

Medicago sativa L.is known as “the King of forage”,with wide adaptability,well developed root system,good quality,rich nutrition,and great value of utilization.It can meet the nutritional needs of livestock include protein,energy,minerals and vitamins,and is a famous grass in forage research.Medicago f alcata L.is widely distributed in China,although it is less regenerative and productive than Medicago sativa L.,because of its resistance to barren and drought resistance,it is suitable to planting in arid areas.In recent years,the planting area of alfalfa has been expanding and has become a pillar industry.However,alfalfa is usually affected by drought stress during growth,which leads to the decline of yield and even death.Therefore,it is of great important to study the effects of drought stress on alfalfa.Drought stress is the main limiting factor to alfalfa production,which could occur in every stages during the growth and development in alfalfa,and could affect the morphogenesis.In this study,drought-resistant alfalfa M1(Medicago sativa L.)and drought-resistant alfalfa M2(Medicago falcata L.)cultivar which breed by ourselves be used.Based on the morphological and physiological responses of alfalfa under PEG-6000 drought stress,transcriptome technique was used to analyze the root system’drought responses of M1 and M2 at seedling stage.The physiological and molecular biological basis of drought resistance difference between M1 and M2 were revealed,and the drought resistance ability of M1 and M2 be analyzed.The drought-resistant genes of alfalfa were initially excavated.The main results are as follows.(1)To study the germination characteristics of alfalfa under different concentrations of PEG-6000(4%,8%,12%,16%,20%,24%,28%,32%).The results show that,with the increase of PEG concentration,the germination rate,relative germination rate,germinating potential and germination index showed a decreasing trend,when the treatment concentration reached 12%,most of the seed germination indexes of M1 and M2 were significantly different from those of the control.Therefore,12% PEG was selected as the optimum concentration of alfalfa drought stress during the seedling stage.(2)The conductivity and MDA content of M1 were higher than that of M2,and the cell membrane damage of M1 was greater than that of M2 under 12% PEG drought stress condition.The activity of SOD,POD and CAT showed the trend of increased at first and decreased subsequently.The seedlings of two kinds of alfalfa,22 days old,had already produced drought stress at 6h treatment of 12% PEG,and the drought stress of 18 h had reached the limit of their self-repair.(3)Transcriptome sequencing of M1 root in seedling stage under 6h and 18 h drought stress,obtained 94739 unigene,N50 was 1167 bp,control group have 82408(86.98%)genes expressed,87841(92.72%)genes were expressed under 6h treatment,and 87869(92.75%)genes were expressed under 18 h treatment.Through protein coding box prediction and sequence annotation,a total of 65846 unigenes with annotated results were obtained.There were 9346 differentially expressed genes between 6h drought stress and control.There were 19443 differentially expressed genes between 18 h and control,and 3462 genes with significant difference were expressed between 6 h and 18 h stress.(4)A total of 114347 unigenees were obtained by sequencing of M2 root in seedling stage under 6h and 18 h drought stress of 12% PEG,N50 was 1130 bp.In the control group,there were 103077(90.14%)genes expressed,102658(89.78%)genes were expressed at 6h treatment,and 102608(89.73%)genes were expressed at 18 h treatment.74900 unigenees were obtained by protein coding frame prediction and sequence annotation.There were 6180 differentially expressed genes between 6h and control,6534 differentially expressed genes betw een 18 h drought stress and control,1050 differentially expressed genes between 6h and 18 h drought stress.(5)To compared the transcriptome sequencing results of M1 and M2 under drought stress,the homologous genes family of the two alfalfa species were 27848,homologous genes were 65812.Go analys is mainly concentrates on the cell processing,response to stimuli and other items in the biological process,cell component was not significantly enr iched.Most differentially expressed genes are enriched with binding and catalytic activity items in molecular functional.KEGG enrichment analysis showed significant enrichment to plant-pathogen interaction and cyanide-amino acid metabolism.