| Drought is one of the main natural disasters that cause the yield loss of maize,one of the major crops in China.Making greater efforts to deepen the study of the genetic and molecular machenism of maize drought response is in urgent need in order to improving maize yield and secure the food safety of the country.Clade A PP2 C phosphatases(PP2CA),which are conserved in most plant species,play important roles in abscisic acid(ABA)signaling and plant drought response.However,natural variations of PP2 CA genes that are directly associated with drought resistance remain to be elucidated.we conducted a candidate gene association analysis of 13 ZmPP2 CA genes using the survival rates of seedlings under drought stress in a maize panel consisting of 368 varieties collected worldwide,and identified some single nucleotide polymorphism(SNP)located in ZmPP2CA10 that are significantly association with drought resistance.ZmPP2CA10,like its Arabidopsis orthologs,interacts with ABA receptors ZmPYLs and ZmSnRK2 kinases,suggesting that ZmPP2CA10 is involved in mediating ABA signaling in maize.Transgenic studies in maize and Arabidopsis confirmed that ZmPP2CA10 functions as a negative regulator of drought resistance.By resequencing,we detected a natural mutation in the promoter of ZmPP2CA10,InDel-338,which is highly correlated with drought resistance.Del-338,which bears a deletion of ERSE(endoplasmic reticulum stress response element)causes the loss of ZmbZIP17 or ZmbZIP60-mediated endoplasmic reticulum stress-induced expression of ZmPP2CA10,leading to increased plant drought resistance.Our study provides direct evidence that ER stress signal is associated with plant drought resistance and the variation has the potential to be used as a molecular marker for drought-resistant maize cultivars.Small RNAs(sRNAs),as important components in regulating gene expression,have been shown to play important roles in control of plant abiotic stress responses.Previously,our laboratory performed sRNA sequencing of 338 maize inbred lines under normal growth conditions and drought treatments.Further whole genome-wide association analysis(GWAS)showed that a drought-induced eQTL hotspot,which is located in chromosome 8,affects the expression levels of multiple sRNAs.How this eQTL hotspot regulates the expression of sRNAs under drought stress,and whether it influences the plant drought resistance remains to be revealed.In this project,we found a natural insertion/deletion of a 21.4Kb inverted repeat(IR-8)in the eQTL,which is significantly associated with sRNA expression levels under drought stress.Further,IR-8 is located in the intron of a PP2 C clade A gene,ZmABI,and its transcription is highly related to ZmABI expression and induced by drought,leading to that the expression levels of sRNAs are notably different in maize inbred lines after drought stress.IR-8 insertion allele(In-IR)is associated with reduce plant drought resistance.Moreover,this insertion represses the expression of ZmABI-T01.ZmABI-P01 protein could interact with kinase ZmOST1,and the inhibitory effect of ZmABI-P01 on ZmOST1 is weaker than that of ZmPP2CA10 on ZmOST1.We thus deduced that ZmABI and ZmPP2CA10 may be competitive in combination with ZmOST1 and further inhibit the kinase activity of ZmOST1,which may affect the response of plant to drought.Meanwhile,we found that siRNA derived from IR-8 can reduce the expression of target genes via mRNA cleavage.These results suggest that the IR-8-insertion in ZmABI locus may affect plant drought resistance via affecting the expression of ZmABI-T01,or by regulating the expression of the target genes in a manner of siRNA-mediated mRNA cleavage.In summary,through analysising the widespread natural variation in maize associated populations,we detected some natural variations that are significantly associated to drought resistance and dissected their mechanism in drought response.Our studies provide theoretic knowledges and genetic markers for breeding drought-resistant maize cultivars. |
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