Rht18 Semidwarfism in Wheat Is Due to Increased GA 2-oxidaseA9 Expression and Reduced GA Content

Abstract

Semidwarfing genes have improved crop yield by reducing height, improving lodging resistance, and allowing plants to allocate more assimilates to grain growth. In wheat (), the semidwarfing gene was identified and deployed in durum wheat before it was transferred into bread wheat, where it was shown to have agronomic potential., a dominant and gibberellin (GA) responsive mutant, is genetically and functionally distinct from the widely used GA-insensitive semidwarfing genes and In this study, the gene was identified by mutagenizing the semidwarf durum cultivar Icaro () and generating mutants with a range of tall phenotypes. Isolating and sequencing chromosome 6A of these "overgrowth" mutants showed that they contained independent mutations in the coding region of is predicted to encode a GA 2-oxidase that metabolizes GA biosynthetic intermediates into inactive products, effectively reducing the amount of bioactive GA (GA). Functional analysis of the GA2oxA9 protein demonstrated that GA2oxA9 converts the intermediate GA to the inactive metabolite GA Furthermore, showed higher expression of and lower GA content compared with its tall parent. These data indicate that the increased expression of in results in a reduction of both bioactive GA content and plant height. This study describes a height-reducing mechanism that can generate new genetic diversity for semidwarfism in wheat by combining increased expression with mutations of specific amino acid residues in .

Dissection of two quantitative trait loci with pleiotropic effects on plant height and spike length linked in coupling phase on the short arm of chromosome 2D of common wheat (Triticum aestivum L.)

“…To date, several genes controlled PHT have been cloned in wheat, such as Rht - B1 , Rht - D1, TaSTE and GA2oxA9 ( Rht18 ) (Ford et al 2018; Gasperini et al 2012; Peng et al 1999; Zhang et al 2013b). Specifically, Rht - B1 and Rht - D1 encoded transcriptional factors belong to the GRAS family (Peng et al 1999; Sun 2010).…”

A wheat dominant dwarfing line with Rht12, which reduces stem cell length and affects gibberellic acid synthesis, is a 5AL terminal deletion line

“…The TraesCS5A01G543100 gene located in the 483‐kb region encodes GA2‐β‐dioxygenase, which is a member of the GA 2‐oxidase (GA2ox) family, which is involved in the GAs metabolism. GA2‐β‐dioxygenase catalyzes the 2‐beta‐hydroxylation of GAs precursors, hydroxylating the C20‐GA GA 12 and GA 53 to GA 110 and GA 97 , which cannot be converted into active GAs (Smith and Macmillan, ; Thomas et al ., , ; Schomburg et al ., ; Pearce et al ., ; Ford et al ., ). Transcriptome analyses results showed negligible TraesCS5A01G543100 expression in the high stalk lines (in both BC 4 F 2 dd and CS), but high expression in dwarf lines (in both BC 4 F 2 DD and N98‐2105).…”

“…Transcriptome analyses reflect the high expression pattern of TraesCS5A01G543100 ( TaGA2ox‐A14 ) in Rht12 lines. The expression product of TaGA2ox‐A14 decreased GA levels and created dwarf plants (Schomburg et al ., ; Lo et al ., ; Ford et al ., ). This further supports the assumption that Rht12 affects the GA biosynthesis pathway in wheat.…”

“…In wheat, genes involved in GA metabolic pathway show comprehensive expression and fuctional characterization (Pearce et al ., ). Recently, GA‐responsive dwarfing gene Rht18 was found to reduce GA 1 content by upregulating TaGA2oxA9 which encodes GA metabolic enzyme GA 2‐oxidase (GA2ox) that metabolizes GA biosynthetic intermediate GA 12 into inactive product GA 110 (Ford et al ., ). Rht24 and Rht25 , two newly discovered GA‐responsive genes, were reported in common wheat; however, the mechanisms remain unclear and the genes have yet to be cloned (Mo et al ., ; Würschum et al .…”

Identification and characterization of Rht25, a locus on chromosome arm 6AS affecting wheat plant height, heading time, and spike development

“…The dwarfing alleles of these four named Rht genes on chromosome 6A are GA-responsive (McIntosh et al 2017), a characteristic also demonstrated in this study for QHt.ucw-6AS. Ford et al (2018) have recently shown that the PH reduction by Rht18 was associated with increased expression of the gene encoding GA 2-oxidaseA9 (GA2ox-A9), and that mutations in the coding region of this gene eliminated the semi-dwarf phenotype of the Rht18 mutants. The upregulation of GA2ox-A9 increases the synthesis of inactive forms of GA and reduces the amount of the active forms of GA. Interestingly, GA2ox-A9 maps within the Rht14/18 region ( Fig.…”