| Aluminum (Al) toxicity is considered as one of the primary causes of low rice productivity on acidupland and lowland acid sulfate soils. In the present study, different populations were used to detectquantitative trait loci (QTLs) for Aluminum tolerance. Meanwhile, one of stable QTLs were dissectedinto single genes using secondary F2 populations, derived from the cross between target CSSLs andgenetic background parent, IR24. Then, fine mapping was further conducted for these single genesusing the data of SSR and InDel markers and phenotypic evaluation. The results thus obtained shouldbe useful for rice MAS breeding and map- based cloning of target QTLs. The main conclusions are asfollows:1 Mapping of quantitative trait loci associated with aluminum tolerance inrice (Oryza sativa L.), using recombinant inbred linesIn this study, a mapping population of 81 F11 lines (recombinant inbred lines: RILs),derived from a cross between a japonica variety Kinmaze and an indica variety DV85 bythe single-seed descent methods, was used to detect quantitative trait loci (QTLs) forAluminum tolerance. Aluminum tolerance in roots of two cultivars (Asominori and IR24)of rice was studied using relative root length (RRL) and relative root elongation (RRE).Results indicated that RRE is a parameter more directly related to Al tolerance andconvenient than RRL Furthermore, relative root elongation (RRE) of scedlings whichgrew on nets floating on 0.5mM CaCl2 (pH 4.5) solution with Al stress or non-stressconditions, was evaluated for the Al toxicity tolerance of RILs and the parents at seedlingstage. QTL analysis was performed with Windows QTL Cartographer 1.13a program bycomposite interval mapping, as the result, five QTLs controlling Aluminum toxicitytolerance for RRE were detected on chromosomes 1, 5, 8, 9 and 11, respectively.Individual QTL accounted for 8.64％～18.60％of the phenotypic variation in the RILpopulation. In the five QTLs for RRE, Kinmaze contributed favorable alleles (lessimpaired by stress) for qRRE1 and qRRE9, while DV85 contributed favorable alleles forqRRE5, qRRE8 and qRRE11. Comparing with the other mapping results, QTLs for RRE,which mapped on chromosomes 1,8,9 and 11, appear to be consistent among different rice populations. These QTLs would be highly useful in breeding cultivars tolerant to Altoxicity in marker-assisted selection (MAS) program and map-based cloning forAl-tolerance genes.2 Identification of quantitative trait loci associated with aluminum tolerancein rice (Oryza sativa L.), using backeross inbred linesQuantitative trait loci (QTL) analysis for Al tolerance was performed in rice using amapping population of 98 BC1F10 lines (backcross inbred lines: BILs), derived from across of Al-tolerant cultivar of rice (Oryza sativa L. cv. Nipponbare) and Al-sensitivecultivar (cv. Kasalath). Three characters related to Al tolerance, including root elongationunder non-stress conditions (CRE), root elongation under Al stress (SRE) and the relativeroot elongation (RRE) under Al stress versus non-stress conditions, were evaluated for theBILs and the parents at seedling stage. A total of seven QTLs for the three traits wereidentified. Among them, three putative QTLs for CRE (qCRE-6, qCRE-8 and qCRE-9)were mapped on chromosomes 6, 8 and 9, respectively. One QTL for SRE (qSRE-4) wasidentified on chromosome 4. Three QTLs (qRRE-5, qRRE-9 and qRRE-10) for RRE weredetected on chromosomes 5, 9, 10 and accounted for 9.7％-11.8％of total phenotypicvariation. Interestingly, the QTL qRRE-5 appears to be syntenic with the genomic regioncarrying a major Al tolerance gene on chromosome 6 of maize. Another QTL, qRRE-9,appears to be similar among different rice populations, while qRRE-10 is unique in theBIL population. The common QTLs for CRE and RRE indicate that candidate genesconferring Al tolerance in the rice chromosome 9 may be associated with root growth rates.The existence of QTLs for Al tolerance was confirmed in substitution lines forcorresponding chromosomal segments. These results also provide the possibilities ofenhancing Al tolerance in rice through using marker-assisted selection (MAS) andpyramiding QTLs.3 QTL analysis and fine-mapping for aluminum tolerance in rice(1) Aluminum (Al) toxicity is considered as one of the primary causes of low riceproductivity on acid upland and lowland acid sulfate soils. In the present study,quantitative trait loci (QTLs) controlling Al tolerance based on relative rootelongation (RRE) were dissected using a complete linkage map and arecombinant inbred lines (RILs) derived from a cross of Al-tolerant japonica cultivar Asominori and Al-sensitive indica cultivar IR24. A total of three QTLs(qRRE-1, qRRE-9 and qRRE-11) were detected on chromosomes 1, 9 and 11 withLOD score ranging from 2.64 to 3.60 and the total phenotypic variance explainedfrom 13.5％to 17.7％. The Asominori alleles were all associated with Altolerance at all the three QTLs. The existence of these QTLs was confirmed usingAsominori chromosome segment substitution lines (CSSLs) in IR24 geneticbackground (IAS). By QTL comparative analysis, the two QTLs (qRRE-1 andqRRE-9) on chromosomes 1 and 9 appeared to be consistent among different ricepopulations while qRRE-11 was newly detected and syntenic with a major Altolerance gene on chromosome 10 of maize. This region may provide animportant case for isolating genes responsible for different mechanisms ofaluminum tolerance among different cereals. These results also provide thepossibilities of enhancing Al tolerance in rice breeding program bymarker-assisted selection (MAS) and pyramiding QTLs.(2) Phenotypic values were significantly different between the recurrent parent,cultivar IR24, and the six CSSLs harboring qRRE-9 allele, indicating the effectsof the qRRE-9 allele were significant and stable. Based on F2 and F3 populationsderived from the cross of CSSL51 and IR24, the QTL qRRE-9 was dissected intoa single gene, namely, the Alt-9 allele in Asominori was a recessive gene, Alt-9,controlling Aluminum tolerance. Then, the Alt-9 gene was further mappedbetween RM24702 and ID47-2 on chromosome 9, and co-separated withRM5765, using the 1043 CSSL51/IR24 F2 plants and SSR/InDel markers.4 Selection and identification of aluminum-sensitive mutant by T-DNAinsertion in Rice (Oryza sativa L.)As the nearly completed rice genome sequence is currently public available, T-DNAinsertional mutagenesis has been successfully used as a powerful tool to identify a numberof genes in rice. To identify aluminum-responsive genes in rice, we screened T-DNAtagging lines that had been subjected to aluminum toxicity stress at 100μM Al3+ (pH 4.5).The T-DNA-tagged lines were previously constructed through transformation of vectorpDsBar1300 into Nipponbare (Oryza sativa L. subsp, japonica cv. Nipponbare) usingAgrobacterium mediated methods. Vector pDsBar1300 was based on pCAMBIA1300,with an insertion of Ds elements harboring a PHOSPHINOTHRICIN (PPT)-resistance gene bar into the multicloning site of the T-DNA fight side. On the left side of the T-DNA,there is a hygromycin-resistant gene under the control of the CaMV35S promoter forselecting rice transformants. This T-DNA was of the nopalinetype. An aluminum-sensitivemutant caused by T-DNA insertion in rice was identified by measuring root elongationduring a 24-h period. Root elongation of Nipponbare was inhibited by 34％after exposureto100μM Al3+ for 24h, while that of the Aluminum-sensitive Mutant was inhibited by59％. Genetic analysis of the mutant showed that the phenotype of relative root elongationin the segregating populations derived from the T-DNA heterozygotes fit the ratio of 3:1.Test for Basta resistance and hygromycin resistance showed the aluminum toleranceplants were all susceptible whereas the aluminum sensitivity plants were resistant, and theratio of resistant and susceptible plants was nearly 3:1, which indicated that thealuminum-sensitive mutant was co-segregated with Basta resistance and hygromycinresistance. Furthermore, the aluminum-sensitive mutant caused by T-DNA insertion wasconfirmed by T-DNA detection using PCR method. This Aluminum-sensitive mutant willbe used for isolation of the tagged gene in rice. |
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