Physiological And Molecular Mechanisms Underlying Long-distance Cadmium Transport Regulating Plant Cadmium Resistance In Wheat

Soil cadmium pollution is becoming more and more serious.Cadmium pollution seriously restricts agricultural production and threatens human health.Wheat is one of the three major food crops in the world and an important food crop in China.Cadmium pollution in wheat has been reported frequently in recent years.It is an important strategy to study the mechanism of Cd resistance in wheat and to cultivate new varieties of Cd resistance in wheat.In this paper,through the analysis of genetic characteristics,physiological and biochemical changes in roots and abovementis,and through whole-genome resequencing and transcriptome analysis of two different cadmium resistance cultivars,it was found that Ta HMA2b-7A with significantly different expression levels under Cd stress was the cause of different Cd resistance of these two genotypes of wheat.The Ta HMA2b-7A transporter gene was confirmed to play a key role in the determination of cadmium resistance in wheat varieties by transgenic yeast and analysis of the expression level of Ta HMA2b-7A in multiple varieties.The main results are as follows:1.Identification of cadmium resistant and cadmium sensitive wheat varieties and their physiological responses to cadmium stress.According to the degree of cadmium poisoning in leaves,combined with various physiological indicators,Zhengmai 1860(ZM1860)was selected as a cadmium resistant wheat variety,and Zhoumai 32(ZM32)was a cadmium sensitive wheat variety.The translocation coefficients of ZM1860 and ZM32 under 10 μM cadmium treatment were 0.07172 and 0.1271,respectively.The translocation coefficient of ZM32 was significantly higher than that of ZM1860.Therefore,the long-distance transport of cadmium from root to shoot may be the mechanism of different cadmium toxicity resistance between the two wheat cultivars.Antioxidant system detection showed that the content of reactive oxygen species in shoots and roots of ZM32 after cadmium treatment was significantly higher than those of ZM1860,and the activity of antioxidant enzymes in ZM1860 was higher;One reason for the greater cadmium resistance of ZM1860 is its higher antioxidant enzyme activity.2.Genomics DNA sequence variation data analysis and transcriptome comparison analysis of cadmium resistant ZM1860 and cadmium sensitive ZM32 wheat natural lines under cadmium stress.Based on DNA sequence variation analysis of whole genome resequencing of ZM1860 and ZM32,ZM1860 identified 22,352,980 single nucleotide polymorphisms(SNPs)and 1,564,316 insertion/deletion sites(In Dels);ZM32 identified 21,703,776 SNPs and 1,547,608 In Dels.In Del difference of Ta HMA2b-7A gene was identified between ZM1860 and ZM32.Based on transcriptome sequencing results,ZM1860 and ZM32 identified 1,168 and 8,732 differentially expressed genes(DEGs)in response to cadmium stress.GO enrichment analysis was performed on the above DEGs,organic acid biosynthesis,carboxylic acid biosynthesis,cell wall macromolecule synthesis and metabolism,redox enzyme activity and metal ion transmembrane transport activity were significantly enriched in GO.KEGG analyse showed that the glutathione metabolism pathway was the most significant in both root and shoot under cadmium stress.Ta HMA2b-7A gene showed significant difference between ZM1860 and ZM32 varieties under cadmium stress.Through the analysis of Ta HMA2 gene expression and sequence differences,Ta HMA2b-7A was screened as a candidate gene whose root expression was significantly higher in ZM32 than ZM1860 under cadmium stress.3.Functional identification of wheat Ta HMA2 geneThe heterologous expression of Ta HMA2b-7A in yeast resulted in reduced resistance to cadmium,indicating that the Ta HMA2b-7A gene was a cadmium transporter.After cadmium treatment,the expression level of Ta HMA2b-7A gene in 7cd-sensitive wheat varieties was significantly higher than that in 7 cd-resistant wheat varieties.This indicated that Ta HMA2b-7A was the main functional gene that caused the long-distance transport difference between ZM1860 and ZM32 cadmium from root to shoot,and is widely and highly expressed in cadmium sensitive wheat varieties.This study showed that regulating the long distance transport of cadmium from root to shoot is the mechanism of cadmium resistance in cadmium resistant varieties and cadmium sensitive varieties.It provides an important theoretical basis for further study on the mechanism of heavy metal cadmium accumulation in wheat and an important way for the utilization of cadmium-polluted cultivated land..