Abstract
The most common dwarfing genes in wheat, Rht-B1b and Rht-D1b, classified as gibberellin-insensitive (GAI) dwarfing genes due to their reduced response to exogenous GA, have been verified as encoding negative regulators of gibberellin signaling. In contrast, the response of gibberellin-responsive (GAR) dwarfing genes, such as Rht12, to exogenous GA is still unclear and the role of them, if any, in GA biosynthesis or signaling is unknown. The responses of Rht12 to exogenous GA3 were investigated on seedling vigour, spike phenological development, plant height and other agronomic traits, using F2∶3 and F3∶4 lines derived from a cross between Ningchun45 and Karcagi-12 in three experiments. The application of exogenous GA3 significantly increased coleoptile length and seedling leaf 1 length and area. While there was no significant difference between the dwarf and the tall lines at the seedling stage in the responsiveness to GA3, plant height was significantly increased, by 41 cm (53%) averaged across the three experiments, in the GA3-treated Rht12 dwarf lines. Plant height of the tall lines was not affected significantly by GA3 treatment (<10 cm increased). Plant biomass and seed size of the GA3-treated dwarf lines was significantly increased compared with untreated dwarf plants while there was no such difference in the tall lines. GA3-treated Rht12 dwarf plants with the dominant Vrn-B1 developed faster than untreated plants and reached double ridge stage 57 days, 11 days and 50 days earlier and finally flowered earlier by almost 7 days while the GA3-treated tall lines flowering only 1–2 days earlier than the untreated tall lines. Thus, it is clear that exogenous GA3 can break the masking effect of Rht12 on Vrn-B1 and also restore other characters of Rht12 to normal. It suggested that Rht12 mutants may be deficient in GA biosynthesis rather than in GA signal transduction like the GA-insensitive dwarfs.
Highlights
Gibberellins (GAs) are a major class of plant hormones that regulate plant growth and development, from seed germination and stem elongation to fruit-set and growth [1,2,3,4]
Mutants deficient in GA biosynthesis can be rescued by exogenously applied GAs but this is not possible if the mutation is in the GA signaling pathway [7,8]
The Rht12 dwarf lines had a small but significant increase in leaf length over the tall lines, there was no notable difference in its response to exogenous GA3 between dwarf and tall lines (Table 1; Fig. 1)
Summary
Gibberellins (GAs) are a major class of plant hormones that regulate plant growth and development, from seed germination and stem elongation to fruit-set and growth [1,2,3,4]. Mutants with impaired GA biosynthesis or response show typical GA-deficient phenotypes, such as dark green leaves, dwarfism and lateflowering, while elevated exogenous GA dose or increased signaling can cause excessive plant growth and earlier flowering [5,6,7,8]. Mutants deficient in GA biosynthesis can be rescued by exogenously applied GAs but this is not possible if the mutation is in the GA signaling pathway [7,8]. In contrast to the recessive, semi-dwarf sd-1 Green Revolution allele in rice, which is a loss-of-function mutation in one of the major GA biosynthetic genes (GA20ox2) [10,11,12], the reduced height Rht-B1b (Rht1) and
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