Dissecting The Genetic Basis Of Waterlogging Tolerance At Maize Seedling Stage

With the global climate change,waterlogging has become one of the major abiotic stresses to a variety of plants including maize.In order to dissect the genetic basis of waterlogging tolerance at maize seedling stage,we conducted the following study.Firstly,we compared the waterlogging tolerance of two F8 recombinant inbred lines(RILs)(A3237 and A3239)that derived from Mo17 × HuangZao4 at several aspects and mapped the quantitative trait locus(QTL)associated with waterlogging tolerance using segregation populations.Subsequently,genome-wide association study(GWAS)for 8 traits related to waterlogging tolerance was conducted to identify those genetic loci for waterlogging using the association panel containing 368 inbred lines of maize.Finally,the characteristics of 19 ERF-VIIs of maize and the association between their genetic variations and waterlogging tolerance at maize seedling stage were analyzed.The major results are as follow:1.Multiple evidences indicated that A3237 was more tolerant for waterlogging stress than A3239.1)At the phenotype level,7 days(d)after waterlogging stress,the SPAD value,the number of crown root and the fresh weight of root and shoot of A3237 were significantly higher than A3239,but the degree of leaf injury(DLI)was significantly lower in A3237.The analysis of dynamic phenotype of A3237 and A3239 demonstrated that the inhibition of primary root was more obvious in A3237.2)At the physiological level,3 days after waterlogging stress,the content of GSH,ATP and NAD+ decreased much more significantly in A3239,compared to A3237.The increase in ADH activity was smaller in A3237 than A3239.The MDA concentration increased significantly in A3239.3)At the proteomic level,the proteins associated with energy metabolism(enolase,glyceraldehyde-3-phosphate dehydrogenase C subunit 1,and lactate dehydrogenase),the stability of cellular pH(glutamate decarboxylase and malic enzymes)and defence/disease(GSH dehydrogenase,GSH S-transferase TAU 25,and GSH S-transferase phi 8)were specifically enriched in A3237,all of which were important for survival under waterlogged condition.2.Analysis of the genetic polymorphism of A3237 and A3239 using the simple sequence repeat(SSR)markers across the whole genome indicated that the genetic differences were located on chromosome 5(5.03-5.04 bin).Thus,the F2 population were constructed and genetic map was constructed.Combining the phenotype of F3 family,the QTL was mapped to the interval of umc2302 and umc2624.Two traits,WRDW(waterlogging tolerance coefficient of root dry weight)and WTDW(waterlogging tolerance coefficient of total dry weight),were found to be associated with the QTL,and the phenotypic variation explanation was 13.49%and 7.21%,respectively.3.The phenotype of the association panel with 368 inbred lines were investigated under two different environments.The coefficient of waterlogging tolerance of 7 traits(waterlogging tolerance coefficient of root length,WRL;waterlogging tolerance coefficient of seedling height,WSH;waterlogging tolerance coefficient of root fresh weight,WRFW;waterlogging tolerance coefficient of shoot fresh weight,WSFW;WRDW;waterlogging tolerance coefficient of shoot dry weight,WSDW and WTDW)and degree of leaf injury(DLI)were used to calculate the BLUP value,which were used for further analysis.A total of 42 trait-SNP associations were identified through GWAS.These associations were distributed among 18 distinct genomic regions,which were named as genomic region of waterlogging tolerance(GRWT).Among them,16 GRWTs were located within previously identified QTLs while 2 GRWTs were located in novel loci.4.Nineteen group ? ethylene response factors of maize(zmERF-?s)were successfully cloned from B73 genome.The gene structures and possible motifs of them and the phylogenetic relationship among zmERF-?s and ERF-? genes in rice and Arabidopsis were analyzed.Synteny of ERF-? genes in rice,sorghum,Brachypodium and maize genome was also compared.Expression profiles in B73 fifteen tissues from various developmental stages and gene expression in B73 specific tissue of nineteen zmERF-?s genes were conducted.5.The survival rates of the association panel with 368 inbred lines were identified under three different conditions.The candidate gene association(CGA)of 19 zmERF-?s were conducted using SNP markers,and zmERF-?a1.2 was significantly associated with survival rates under all of the 3 distinct conditions and BLUP value,underlying that zmERF-?a1.2 potentially contributed to waterlogging tolerance at maize seedling stage.6.Two hundred and eighty inbred lines from the association panel were randomly selected to re-sequence the zmERF-?a1.2,which included 1.1 kb promoter and 2 kb gene region.A total of 87 polymorphic loci were identified according to the sequence alignment result.Association mapping was conducted using BLUP value,and 7 loci were significantly associated(p<1E-03),which included 3 InDels(InDel-241,InDel214 and InDe11401)and 4 SNPs(SNP-14,SNP-12,SNP983 and SNP1370).InDel-241 was located within 5'-UTR.The expression level in root of zmERF-?a1.2 were analyzed using 60 inbred lines that randomly selected from the resequenced lines.The results indicated that InDel-241 affected the expression level of zmERF-?a1.2 whether the stress existed or not.The expression of zmERF-?a1.2 after 4 h waterlogging stress were positively correlated with phenotype.The zmER-?a1.2 was also overexpressed in Arabidopsis.Four-week-seedlings of transgenic plants were treated with 11 days submergence,and the survival rate of transgenic plants were found to be significantly improved after the stress treatment.