Haplotype dictionary for the Rht-1 loci in wheat

Area of Science:

• Plant genetics
• Molecular biology
• Agricultural science

Background:

• Reduced height (Rht)-B1b and Rht-D1b alleles are key to semi-dwarfism in bread wheat (Triticum aestivum), originating from the 'green revolution'.
• Rht-1 loci encode DELLA proteins, influencing plant growth, stress tolerance, and Fusarium Head Blight resistance.
• Understanding genetic diversity at Rht-1 loci is vital for wheat breeding and crop improvement.

Purpose of the Study:

• To identify and characterize variants within the Rht-A1, Rht-B1, and Rht-D1 loci in bread wheat and related species.
• To assess the genetic diversity and haplotype distribution of Rht-1 alleles in modern and ancestral wheat accessions.
• To investigate the impact of novel polymorphisms on Rht-B1 gene expression.

Main Methods:

• Development of locus-specific primers for sequencing Rht-1 genes and flanking regions.
• Sequencing of open reading frames (ORFs) and flanking regions of Rht-A1, Rht-B1, and Rht-D1 in bread wheat and tetraploid/diploid wheat (TDW).
• Quantitative real-time PCR (qRT-PCR) to analyze Rht-B1 transcript levels in response to identified polymorphisms.

Main Results:

• Bread wheat accessions showed lower genetic diversity at Rht-A1+f and Rht-D1+f compared to Rht-B1+f.
• Tetraploid and diploid wheat (TDW) accessions exhibited higher genetic diversity and contained most polymorphic sites.
• Novel polymorphisms, including insertions 5' of Rht-B1 and a frameshift in the Rht-B1 ORF, were identified. These insertions did not significantly affect Rht-B1 transcript levels.

Conclusions:

• Significant genetic diversity exists at Rht-1 loci, particularly in ancestral wheat accessions.
• Rht-B1 locus harbors more genetic variation and novel polymorphisms compared to Rht-A1 and Rht-D1 in bread wheat.
• The identified polymorphisms offer insights into the evolution and variation of key height-regulating genes in wheat.