Novel genetic variants of GA-insensitive Rht-1 genes in hexaploid wheat and their potential agronomic value.

This study has found numerous novel genetic variants of GA-insensitive dwarfing genes with potential agricultural value for crop improvement. The cultivar, Spica is a tall genotype and possesses the wild-type genes of Rht-A1a, Rht-B1a and Rht-D1a. The cultivar Quarrion possesses a null mutant in the DELLA motif in each of the 3 genomes. This is a first report of a null mutant of Rht-A1. In addition, novel null mutants which differ from reported null alleles of Rht-B1b, Rht-B1e and Rht-D1b have been found in Quarrion, Carnamah and Whistler. The accession, Aus1408 has an allele of Rht-B1 with a mutation in the conserved 'TVHYNP' N-terminal signal binding domain with possible implications on its sensitivity to GA. Mutations in the conserved C-terminal GRAS domain of Rht-A1 alleles with possible effects on expression have been found in WW1842, Quarrion and Drysdale. Genetic variants with putative spliceosomal introns in the GRAS domain have been found in all accessions except Spica. Genome-specific cis-sequences about 124 bp upstream of the start codon of the Rht-1 gene have been identified for each of the three genomes.