Identification And Expression Analysis Of The BrSWEETs Family Members In The Chinese Cabbage-Plasmodiophora Brassicae Interaction

Plasmodiophora brassicae is worldwide a soil borne pathogen of cruciferous plants and the causal agent of clubroot,a devastating disease of Brassica crops.The pathogen lives inside roots,and hijacks nutrients for its own growth and reproduction from the host plants.In plant-pathogen interaction,the pathogenic bacteria obtained sugar from the plant,accompanied by the changing of the sugar transporters SWEET genes expression in plants.Therefore,it can be believed that the SWEET genes plays a crucial role in the interaction between host and pathogenic bacteria while exercising the function of sugar transporter in plants.In this study,a pair of cabbages near-isogenic lines(resistance genotype ’CR222’ and disease genotype ’CS222’)were used test materials,analyzed the variation of the soluble sugar contents after P.brassicae infection.Based on the identification of sugar transporters BrSWEETs genes family members of Chinese cabbage,the difference expression of BrSWEET genes were analyzed in the Chinese cabbage-P.brassicae interaction.The homologous mutant of arabidopsis thaliana with significant difference were disease resistance identified.The results are concluded as following:1.In the process of the cabbage growth,the soluble sugar(fructose,glucose,sucrose)contents in leaves and roots of a pair of Chinese cabbage near-isogenic lines(NILs)did not exist significant differences.But after P.brassicae infection,the fructose and sucrose contents of leaf in the two materials is lower,and the content of glucose is significantly higher from 2 days after inoculation.The fructose,glucose and sucrose contents of CS were significantly lower than CR.After inoculation,the fructose and glucose contents of two material root samples were significantly higher,and sucrose content was lower.The fructose,glucose content of CS was significantly higher than CR after the inoculation,and sucrose content was significantly lower than resistant material.2.We identified 32 SWEETs gene family members with Multi-span membrane structure and have typical MtN3 / saliva conserved domain from Chinese cabbage genome library.The analysis of phylogenetic tree showed that BrSWEETs gene family members belonging to four different groups.The analysis of genetic structure showed that most of the genes contain six exons.There are a variety of cis element participate in the defense stress and hormone response in their promoter.3.The result of tissue specificity expressed shows that 16 genes were expressed in leaves,hypocotyls and roots,four genes(BrSWEET3b,–5a,–5b and –8)did not detected transcription signal.Six genes(BrSWEET7b,-10,-14 a,-14 b,-15 a and-15c)were detected transcriptional signals in the root and hypocotyl,two genes(BrSWEE3a and BrSWEET7a)were detected transcription signals in roots and leaves.There arefour genes only expressed in an tissue,such as BrSWEET16 b only expressed in root,BrSWEET5 c and BrSWEET9 only expressed in the hypocotyl,BrSWEET4 b only expressed in the leaf.4.The expression of 6 genes(BrSWEET3b,-4b,-5b,-5c,-8 and-16b)in the root,7 genes(BrSWEET3a,-3b,-4b,-5b,-7a,-8 and-9)in the hypocotyl,and 4 leaves(BrSWEET8,-9,-10,and-15c)wERE induced by P.brassicae infection.After P.brassicae infection,only BrSWEET5 a did not detected transcription signal in root and hypocotyl.9 genes(BrSWEET3b,–5a,–5b,–5c,–7b,–14a,–14b,–15a and –16b)still not showing in the leaf.5.After P.brassicae infection,the expression of 15 genes(BrSWEET1a,-1b,-2a,-2b,-3a,-4a,-4b,-7a,-8,-10,-13,-14 b,-15 b,-16 a and-17a)are higher in the leaf of CS than CR,among them,six SWEET genes(BrSWEET2b,-14 c,-15 b,-15 c,-16 a and-17a)were significantly up-regulated in CS.There are eleven genes(BrSWEET4a,-5b,-8,-10,-11 a,-11 b,-12 b,-14 c,-15 a,-17 a and-17b)showing down-regulated expression patterns in the hypocotyl,and the remaining 20 genes were up-regulated.Among them,two genes(BrSWEET9 and 16a)expression were found significantly higher in CS than in CR.In the root,22 BrSWEETs were up-regulated more than 10 times,while the 7 genes(BrSWEET5c,-11 b,-11 c,-12 a,-13,-14 c and-15a)were up-regulated within 10 times.Most notably,the expression of BrSWEET1 a,–2a and –11a were reached more than 6000 times in the root.6.After P.brassicae infection,the growth and growth status of mutant strains(sweet1,sweet2,sweet11)were significantly better than those in the wild type,the disease index(DI)and P.brassicae DNA content of mutants were significantly lower than the wild type.sweet mutant was significantly reduced the sensitivity of the plant to P.brassicae infection,delayed the plant response to P.brassicae infection,ultimately delay the development of plant P.brassicae infection process.