Dataset Information

Genome-wide association study and candidate gene analysis of alkalinity tolerance in japonica rice germplasm at the seedling stage.

ABSTRACT:

Background

Salinity-alkalinity stress is one of the major factors limiting rice production. The damage caused by alkaline salt stress to rice growth is more severe than that caused by neutral salt stress. At present, the genetic resources (quantitative trait loci (QTLs) and genes) that can be used by rice breeders to improve alkalinity tolerance are limited. Here, we assessed the alkalinity tolerance of rice at the seedling stage and performed a genome-wide association study (GWAS) based on genotypic data including 788,396 single-nucleotide polymorphisms (SNPs) developed by re-sequencing 295 japonica rice varieties.

Results

We used the score of alkalinity tolerance (SAT), the concentrations of Na⁺ and K⁺ in the shoots (SNC and SKC, respectively) and the Na⁺/K⁺ ratio of shoots (SNK) as indices to assess alkalinity tolerance at the seedling stage in rice. Based on population structure analysis, the japonica rice panel was divided into three subgroups. Linkage disequilibrium (LD) analysis showed that LD decay occurred at 109.77 kb for the whole genome and varied between 13.79 kb and 415.77 kb across the 12 chromosomes, at which point the pairwise squared correlation coefficient (r²) decreased to half of its maximum value. A total of eight QTLs significantly associated with the SAT, SNC and SNK were identified by genome-wide association mapping. A common QTL associated with the SAT, SNC and SNK on chromosome 3 at the position of 15.0 Mb, which explaining 13.36~13.64% of phenotypic variation, was selected for further analysis. The candidate genes were filtered based on LD decay, Gene Ontology (GO) enrichment, RNA sequencing data, and quantitative real-time PCR (qRT-PCR) analysis. Moreover, sequence analysis revealed one 7-bp insertion/deletion (indel) difference in LOC_Os03g26210 (OsIRO3) between the alkalinity-tolerant and alkalinity-sensitive rice varieties. OsIRO3 encodes a bHLH-type transcription factor and has been shown to be a negative regulator of the Fe-deficiency response in rice.

Conclusion

Based on these results, OsIRO3 maybe a novel functional gene associated with alkalinity tolerance in japonica rice. This study provides resources for improving alkalinity tolerance in rice, and the functional molecular marker could be verified to breed new rice varieties with alkalinity tolerance via marker-assisted selection (MAS).

SUBMITTER: Li N

PROVIDER: S-EPMC6459459 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Rice in tropical and sub-tropical areas is often subjected to cold stress at the seedling stage resulting in poor growth and yield loss. In general, japonica rice has stronger cold tolerance (CT) than indica rice. However, several favorite alleles for CT exist in indica rice and can be used to enhance CT under japonica background. Genome-wide gene expression profiling is the efficient way to decipher the molecular genetic mechanism of CT enhancement and provide valuable information for the CT improvement in rice molecular breeding. In this study, the transcriptome of a CT introgressed line (IL) K354 and its recurrent parent C418 under cold stress were comparatively analyzed to explore the possible CT enhancement mechanism of K354.Totally 3184 differentially expressed genes (DEGs) including 195 transcription factors were identified in both lines under cold stress, about half of them were commonly regulated, which were involved in the major cold responsive pathways including OsDREB1s regulon. The K354-specific cold-induced DEGs were mainly related to stimulus response, cellular cell wall organization, and microtubule-based movement process compared with commonly cold-induced DEGs by GO analysis. Moreover, 296 constitutive DEGs with significantly different transcription level between C418 and K354 were detected under both control and cold stress conditions. K354-specific cold-regulated and constitutive DEGs jointly account for the CT improvement of K354. Pathway analysis unraveled up-regulation of starch and sucrose metabolism in both genotypes and presumably weaker defense response to stress in K354 than C418 under cold stress. Candidate genes prediction based on previous putative CT genetic networks revealed genotype-dependent CT enhancement mechanism in CT IL K354 vs recurrent parent C418, including Sir2, OsFAD7, OsWAK112d, and PCD related genes, etc.We propose a hypothesis of the CT enhancement mechanism in rice based on the results in present study. Firstly, a number of cold-regulated genes are able to express constitutively at high level or absent under control condition for standing by the arrival of cold stress. Next, under cold stress slower perception of stress signal from the more cold-tolerant membrane can postpone the activation of defensive system which may have possible negative effects on rice growth. Then, PCD will be launched to sacrifice a few cells for maintaining the basal growth of most cells. Finally, the protective responses on multiple aspects of cold damage will be postponed because of delayed several cold-defensive pathways (i.e. OsDREB1C regulon). It might explain why the recovery capacity of K354 from cold stress to control condition is stronger than C418. The CT enhancement mechanism can be regarded as the possible way to improve CT of japonica rice using indica germplasm in rice breeding program.