| China is a major rice producer and also a country with severe water shortages.Screening rice germplasm for drought resistance is of great significance for breeding drought-resistant varieties suitable for water-saving rice cultivation,saving the limited water resources,and alleviating the current situation of urgent agricultural water use.In this study,we used Introgression Restorer Line and common rice varieties to identify and screen drought-resistant rice germplasm in the field through water-dry cultivation mode and conventional water management mode(CK)respectively.In addition,the genetic diversity was studied on a transcription factor DREB2 A gene related to drought resistance in different types of rice germplasms.The functional nucleotide sequence variation of DREB2 A in different types of rice germplasm and the influence on rice drought resistance were explored using haplotype analysis,phylogenetic tree,genetic distance and codon preference analysis.This study provided elite germplasms and molecular basis for breeding of drought-resistant varieties.The main results are as follows:1.Statistical analysis of the drought resistance coefficient(DC value)of different traits showed that the DC value varies from 0.07 to 1.45.Coefficients of variation of the DC values of most traits of the tested materials were over 10%.The coefficient of variation of PN,SSR and YPP scored 31.94%,30.14% and 33.59%,respectively.2.Based on DC value,the 60 tested materials were classified into seven groups.Group I was composed of 19 materials,including 7 common rice varieties,10 Introgression Restorer Lines and 2 NERICA varieties;Group II was composed of 13 materials,including 8 common rice varieties and 5 Introgression Restorer Lines;Group III was composed of 5 materials,including 1 common rice varieties and 4 Introgression Restore Lines;Group IV was composed of 6 materials,including 3 Introgression Restore Lines and 3 common rice varieties;Group V was composed of 2 materials,including 1common rice variety and 1 Introgression Restore Line;Group VI was composed of 8materials,including 5 common rice varieties,1 Introgression Restore Line and 2 NERICA varieties;Group VII was composed of 7 materials,including 3 common rice varieties and 4Introgression Restorer Lines.Multiple comparisons between the seven groups of materials showed that there were significant differences in seed setting rate,yield per plant,plant height,1000-grain weight,and number of grains per panicle.Based on the D value,a comprehensive evaluation of the drought resistance of rice was carried out.The results showed that the drought resistance grades of 60 test materials can be divided into 4grades,including 6 strong drought resistance materials(D≥0.7)and 45 medium drought resistance materials(0.50≤D<0.70),7 parts with weak drought resistance materials(0.3≤D<0.50),2 parts without drought resistance materials(D<0.3).3.Grey correlation analysis and stepwise regression analysis showed that 1000-grain weight,number of grains per panicle,seed setting rate,yield per plant,panicle length and effective panicle number could be used as key indicator traits for evaluating drought tolerance of rice.The correlation degrees of D values of 6 traits were 0.7096,0.7331,0.7229,0.7698,0.6967,and 0.6973,respectively;the correlation degrees of WDC values of 6 traits were 0.7396,0.7412,0.7129,0.7488,0.6943,and 0.7011,respectively.4.The nucleotide sequence variation of 85 DREB2 A gene transcripts derived from different germplasm materials was excavated,and a total of 55 nucleotide variation sites were detected;a total of 12 amino acid sequences were obtained by translation,and 10 were identified.There were several amino acid variation sites,and the amino acid sequence derived from Oryza glaberrima material had a larger fragment variation.5.Haplotype analysis was performed on the nucleotide sequences of a transcription region in the homologous DREB2 A genes from 85 rice materials.A total of 39 haplotypes were identified,of which 33 newly discovered haplotypes were uploaded to the Gen Bank database(accession number is MN436756～MN436788),the remaining 6 haplotypes were identical to those of previous reports.The haplotypes of the DREB2 A gene could be divided into three groups based on their topological relationships.6.Phylogenetic analysis showed that the 39 haplotypes of the DREB2 A gene were also divided into 3 groups.Group III had the largest genetic distance;group I followed;and group II had the smallest genetic distance.The genetic distance between group I and III was the largest;followed by that between group II and III;and the smallest genetic difference was between group I and group II.Variance analysis on the haplotypes and phenotypic traits of group I and group II showed that the two groups of haplotype materials were significant different in the number of grains per panicle,seed setting rate and yield per plant.7.Codon preference analysis showed that the ENC value of the DREB2 A gene was exceptionally large(up to 61).A cluster analysis of the RSCU values of 12 DREB2 A alleles revealed that the codon usage of DREB2 A gene in African rice was different from that of the other rice materials. |
