Genome-Wide Analysis of ZmDREB Genes and Their Association with Natural Variation in Drought Tolerance at Seedling Stage of Zea mays L
(A) Haplotypes of ZmDREB2.7 in CIMBL70, 91, 92, CML118, Shen5003 and B73 (as reference genome) maize genotypes. The site of the start codon (ATG) was designated as “+1”. SNP-503, SNP-260, SNP-150, InDel-185 and InDel-154 are the five DNA polymorphisms significantly associated with maize drought tolerance and are located in the 5′-UTR of ZmDREB2.7. The 20-bp InDel upstream of the ATG is in complete LD with the five polymorphisms in the four drought tolerant varieties. These polymorphisms are shaded in red. The location of PCR primers used for genotyping the InDel polymorphism of ZmDREB2.7 in drought tolerant (CIMBL70, 91, 92, and CML118) and drought sensitive (Shen5003) inbred lines are indicated by arrows. The four significant nonsynonymous polymorphisms in the coding region of InDel141, SNP142, SNP436 and SNP661 are shaded in blue. (B) Phenotypic response of CIMBL70, 91, 92, CML118 and Shen5003 to drought stress. The upper panel is a photo of plants growing under favorable water conditions while the lower panel plants re-watered for 6 days after the drought stress treatment was terminated. (C) The survival rate of CIMBL70, 91, 92, CML118 and Shen5003 plants exposed to moderate and severe drought stress. Data represent the mean of triplicates (t-test, *p<0.05, **p<0.01). (D) Relative level of ZmDREB2.7 expression in CIMBL70, 91, 92, CML118 and Shen5003 grown under normal and drought stress conditions. The drought-stress treatment reflected a decrease in RLWC from 98% (unstressed) to 70% (moderate drought), and 58% (severe drought). Data represent the mean of three biological replicates (t-test, **p<0.01). (E) The effect of the ZmDREB2.7 favorable allele on drought tolerance in four F2 segregating populations of maize. In each population, three distinct genotypes for ZmDREB2.7 were identified by DNA amplification: homozygous for the favorable allele, homozygous for the sensitive allele, and heterozygous for both alleles. The survival rate of the different genotypes was assessed and compared in the four populations. N indicates the number of F2 individuals tested in each population (t-test, *p<0.05, **p<0.01).