Overgrowth (Della) mutants of wheat: development, growth and yield of intragenic suppressors of the Rht-B1c dwarfing gene

Abstract

A suppressor screen using the dwarf Rht-B1c Della mutant of wheat (Triticum aestivum L.) led to the isolation of overgrowth mutants, which retained the original dwarfing gene but grew at a faster rate because of a new mutation elsewhere in that gene. Forty-six alleles were identified, which included amino acid substitutions, premature stop codons, and splice site alterations. The sites of amino acid substitution were primarily localised around conserved motifs in the DELLA protein, and these mutants showed a wide range in their extent of growth recovery (dwarf, semidwarf, tall). Detailed growth comparisons were made on a wide height range of backcrossed overgrowth alleles, comparing stem and spike growth, leaf size, tillering, phenological development, coleoptile length, grain dormancy and grain yield. There were large and reproducible differences between alleles for some traits, whereas others were largely unaffected or varied with growth conditions. Some of the overgrowth alleles offer promise as alternatives to the Rht-B1b and Rht-D1b dwarfing genes, allowing a wider range of height control, improved grain dormancy and equivalent grain yield. The collection of mutants will also be valuable as a resource to study the effect of height on different physiological or agronomic traits, and in elucidating DELLA protein function.

Manipulating Gibberellin Control Over Growth and Fertility as a Possible Target for Managing Wild Radish Weed Populations in Cropping Systems

“…This differing response to paclobutrazol is consistent with overgrowth allele-specific differences for other GA-related traits such as a-amylase production and grain size (Chandler and Harding, 2013). Of the 27 Rht-B1 suppressor alleles that exist in wheat, four of these reside within the PFYRE domain (Rht-B1c.15 to Rht-B1c.18) (Chandler and Harding, 2013;Derkx et al, 2017). Rht-B1c.15 is a strong candidate as a semi-dwarfed paclobutrazol resistance wheat variety as it carries the same Arg(R) to His(H) substitution as the barley sln1d.9.…”

“…In accordance almost all of the identified sln1 and rht-B1 overgrowth mutations, reside within domains involved in mediating protein-protein interactions responsible for the intrinsic repression activity of DELLA proteins (Hirano et al, 2010;Hirano et al, 2012;Chandler and Harding, 2013;Derkx et al, 2017;Van De Velde et al, 2017b). The wheat overgrowth mutations frequently occur in the LHRI and PFYRE domains, and only occur in these domains for barley (Derkx et al, 2017). Their distribution occurs throughout LHRI, but reside only in the tail end of PFYRE domain.…”

“…Therefore the different responses of the sln1 overgrowth alleles to paclobutrazol and GA treatments, are an outcome of an intricate interplay between GA concentrations, resistance of sln1 to GA-mediated degradation, and the constraint on triggering growth suppression processes imposed by the secondary overgrowth mutation. In accordance almost all of the identified sln1 and rht-B1 overgrowth mutations, reside within domains involved in mediating protein-protein interactions responsible for the intrinsic repression activity of DELLA proteins (Hirano et al, 2010;Hirano et al, 2012;Chandler and Harding, 2013;Derkx et al, 2017;Van De Velde et al, 2017b). The wheat overgrowth mutations frequently occur in the LHRI and PFYRE domains, and only occur in these domains for barley (Derkx et al, 2017).…”

“…Theoretically, a strong "GA-insensitive" DELLA mutant would confer the best resistance to general GA inhibitors given their indifference to GA levels. However, such alleles would be excessively detrimental to plant growth with even moderately strong alleles in barley (sln1d) and wheat (Rht-B1c) being too dwarfed for agricultural purposes (Chandler and Harding, 2013;Derkx et al, 2017). Therefore the "ideal" mutant would be a DELLA protein that is largely insensitive to GA levels, with a diminished growth-suppressing activity, that offsets growth reductions to within a more acceptable range.…”

“…This second approach is likely more practical as it does not require the development of new chemicals and approval for use in an agricultural setting. The overgrowth alleles are already being integrated into cereal breeding programs because of their semi-dwarfing growth, improved grain characteristics, and potential benefits toward several other important agronomic traits regulated by DELLAs (Chandler and Harding, 2013;Derkx et al, 2017;Serrano-Mislata et al, 2017;Thomas, 2017;Van De Velde et al, 2017a;Van De Velde et al, 2017b;Mo et al, 2018;Moriconi et al, 2019). Some of these overgrowth alleles will also have the added benefit of conferring resistance to GA inhibitors, extending the potential agricultural applications of these overgrowth alleles.…”