Association of SNP Haplotypes of HKT Family Genes with Salt Tolerance in Indian Wild Rice Germplasm.

BACKGROUND: Rice is one of the most important crops for global food security but its productivity is adversely affected by salt stress prevalent in about 30 % of the cultivated land. For developing salt-tolerant rice varieties through conventional breeding or biotechnological interventions, there is an urgent need to identify natural allelic variants that may confer salt tolerance. Here, 299 wild rice accessions collected from different agro-climatic regions of India were evaluated during growth under salt stress. Of these 95 representative accessions were sequenced for members of HKT ion transporter family genes by employing Ion Torrent PGM sequencing platform. RESULTS: Haplotype analysis revealed haplotypes H5 and H1 of HKT1;5 and HKT2;3, respectively associated with high salinity tolerance. This is the first study of allele mining of eight members of HKT gene family from Indian wild rice reporting a salt tolerant allele of HKT2;3. HKT1;5 also showed a salt tolerant allele from wild rice. Phylogenetic analysis based on the nucleotide sequences showed different grouping of the HKT family genes as compared to the prevailing protein sequence based classification. CONCLUSIONS: The salt tolerant alleles of the HKT genes from wild rice may be introgressed into modern high yielding cultivars to widen the existing gene pool and enhance rice production in the salt affected areas.

Single-copy gene based 50 K SNP chip for genetic studies and molecular breeding in rice.

Single nucleotide polymorphism (SNP) is the most abundant DNA sequence variation present in plant genomes. Here, we report the design and validation of a unique genic-SNP genotyping chip for genetic and evolutionary studies as well as molecular breeding applications in rice. The chip incorporates 50,051 SNPs from 18,980 different genes spanning 12 rice chromosomes, including 3,710 single-copy (SC) genes conserved between wheat and rice, 14,959 SC genes unique to rice, 194 agronomically important cloned rice genes and 117 multi-copy rice genes. Assays with this chip showed high success rate and reproducibility because of the SC gene based array with no sequence redundancy and cross-hybridisation problems. The usefulness of the chip in genetic diversity and phylogenetic studies of cultivated and wild rice germplasm was demonstrated. Furthermore, its efficacy was validated for analysing background recovery in improved mega rice varieties with submergence tolerance developed through marker-assisted backcross breeding.

Natural allelic diversity in OsDREB1F gene in the Indian wild rice germplasm led to ascertain its association with drought tolerance.

KEY MESSAGE: Three coding SNPs and one haplotype identified in the OsDREB1F gene have potential to be associated with drought tolerance in rice. Drought is a serious constraint to rice production worldwide, that can be addressed by deployment of drought tolerant genes. OsDREB1F, one of the most potent drought tolerance transcription activator genes, was re-sequenced for allele mining and association study in a set of 136 wild rice accessions and four cultivated rice. This analysis led to identify 22 SNPs with eight haplotypes based on allelic variations in the accessions used. The nucleotide variation-based neutrality tests suggested that the OsDREB1F gene has been subjected to purifying selection in the studied set of rice germplasm. Six different OsDREB1F protein variants were identified on the basis of translated amino acid residues amongst the orthologues. Five protein variants were truncated due to deletions in coding region and found susceptible to drought stress. Association study revealed that three coding SNPs of this gene were significantly associated with drought tolerance. One OsDREB1F variant in the activation domain of OsDREB1F gene which led to conversion of aspartate amino acid to glutamate was found to be associated with drought tolerance. Three-dimensional homology modeling assisted to understand the functional significance of this identified potential allele for drought tolerance in rice. The natural allelic variants mined in the OsDREB1F gene can be further used in translational genomics for improving the water use efficiency in rice.