Identification and Characterization of Novel Reduced Height Alleles Using Gibberellic Acid Responsiveness Assays and Predictive Modeling.

The introduction of semi-dwarfing genes into wheat significantly contributed to the yield increases associated with the ‘Green Revolution’. The original semi-dwarfing genes were mutations of the Reduced Height gene (Rht), termed Rht-B1b and Rht-D1b. Both mutant alleles contain stop codons near the RHT N terminus, resulting in a truncated limiting wheat’s ability to respond to Gibberellic Acid (GA). Rht-B1b and Rht-D1b reduce plant height by 15-20% and increase harvest index, yield, and productive tillers. However, Rht-B1b and Rht-D1b also decrease coleoptile length, seed protein content, and seedling emergence. Furthermore, either Rht-B1b or Rht-D1b have been incorporated into over 80% of all wheat cultivars, and there is limited useful Rht allelic diversity beyond these two mutant alleles. The primary objective of this project is characterize new Rht alleles that could be incorporated into wheat varieties. To accomplish this, the standard height variety Fortuna was mutagenized with EMS and Rht-A1, Rht-B1, and Rht-D1 mutations were identified. In total, thirteen Rht missense mutations were identified as well as a single nonsense mutation in each gene. The impact of each mutation upon coleoptile length and GA response was measured and several mutations had coleoptile length and GA response intermediate between wild type and Rht-B1b. These mutations were also predicted to significantly impact RHT protein structure and function based on computational modeling. These mutant lines are now being crossed into spring and winter wheat varieties individually, as well as in combination for further testing to investigate their impact on agronomic traits.