Extraction Of Salt Tolerance Genes In Sugar Beet Based On Transcriptome

Sugar beet(Beta vulgaris L.),one of the major sugar crops,is mainly distributed in arid-semi-arid regions such as Northeast,Northwest and North China.It is an important economic crop with regional characteristics and advantages in Inner Mongolia.With the global climate change,more and more serious soil salinization,which has been already an important factor limiting crop cultivation and yield quality improvement.The physiological and molecular response mechanism of sugar beet under salt stress was studied,and the mechanism of sugar beet adaptation to salt stress were deeply revealed,providing theoretical basis and technical support of further breeding salt tolerant sugar beet varieties.In this study,salt-tolerant and salt-sensitive cultivars were screened from 50varieties.Through transcriptome data analysis,key candidate genes involved in the response to salt stress were found and validated,and physiological and biochemical changes before and after salt stress were comparatively analyzed.The following results are as follows:(1)Transcriptome sequencing analysis of the salt-tolerant and salt-sensitive cultivars showed that the up-regulated differentially expressed genes(DEGs)in leaves and roots were 2237 and 2545 in salt tolerant varieties,respectively,and the numbers of down-regulated DEGs were 2545 and 3056.The number of up-regulated DEGs in the leaves and roots were 936 and 994 in salt-sensitive cultivars,respectively,and the down-regulated DEGs were 994 and 3244,respectively.There were 6712 DEGs(3173up-regulated and 3539 down-regulated)between the two cultivars after salt stress treatment.These genes are mainly involved in cellular processes,metabolic processes,biological regulation,response to stimuli,catalytic activity,and Ion transport.(2)Differentially expressed genes were screened by transcriptomic analysis of salt-tolerant and salt-sensitive varieties under salt stress,and the gene expression validation has been performed by q-PCR.The results showed that 3 genes related to chlorophyll synthesis(CHLG,CHLM,GSA),5 genes related to osmotic regulation(proline metabolism:P5CS1,P5CS2,PDH;betaine synthesis CMO,BADH),3 genes related to reactive oxygen species scavenging system(SOD,CAT,APX,GSS),5 genes related to ion transport(NHX1,KUP13,V-Hppase,ATPase4,TPK1)responded significantly to salt stress,which can be used as a candidate genes for genetic improvement of salt tolerance.(3)After salt stress,the decrease percentage of chlorophyll content,fresh weight and the content of K~+in roots of salt-tolerant cultivar was smaller than those of salt-sensitive cultivar;the activities of antioxidant enzyme,content of oxidized glutathione,hydrogen peroxide,proline,betaine,sucrose,fructose,soluble sugar content and the K~+content in leaves was significantly higher than those of salt-sensitive cultivar,while the Na~+content was significantly lower than that of salt-sensitive cultivar.In summary,the salt-tolerant cultivar exhibited better osmotic regulation ability,maintained high antioxidant enzyme activity and chlorophyll content,strong cell membrane stability and Na~+/K~+balance after salt stress,which are the physiological basis for the high salt tolerance of sugar beet,and these genes related to their metabolism are the salt tolerance genes of sugar beet.