RESUMO
World wheat grain yields increased substantially in the 1960s and 1970s because farmers rapidly adopted the new varieties and cultivation methods of the so-called 'green revolution'. The new varieties are shorter, increase grain yield at the expense of straw biomass, and are more resistant to damage by wind and rain. These wheats are short because they respond abnormally to the plant growth hormone gibberellin. This reduced response to gibberellin is conferred by mutant dwarfing alleles at one of two Reduced height-1 (Rht-B1 and Rht-D1) loci. Here we show that Rht-B1/Rht-D1 and maize dwarf-8 (d8) are orthologues of the Arabidopsis Gibberellin Insensitive (GAI) gene. These genes encode proteins that resemble nuclear transcription factors and contain an SH2-like domain, indicating that phosphotyrosine may participate in gibberellin signalling. Six different orthologous dwarfing mutant alleles encode proteins that are altered in a conserved amino-terminal gibberellin signalling domain. Transgenic rice plants containing a mutant GAI allele give reduced responses to gibberellin and are dwarfed, indicating that mutant GAI orthologues could be used to increase yield in a wide range of crop species.
Assuntos
Proteínas de Arabidopsis , Arabidopsis/genética , Genes de Plantas , Giberelinas/farmacologia , Triticum/genética , Zea mays/genética , Alelos , Sequência de Aminoácidos , Arabidopsis/crescimento & desenvolvimento , Mapeamento Cromossômico , Clonagem Molecular , Etiquetas de Sequências Expressas , Dados de Sequência Molecular , Mutação , Oryza/genética , Proteínas de Plantas/genética , Proteínas de Plantas/fisiologia , Fatores de Transcrição/genética , Fatores de Transcrição/fisiologia , Transformação Genética , Triticum/crescimento & desenvolvimento , Zea mays/crescimento & desenvolvimentoRESUMO
The effects of the 'Tom Thumb' Rht3 dwarfing gene in wheat on plant height, yield components and grain quality in field trials of random inbred lines from two 'Minister Dwarf' (Rht3) x rht3 crosses are described. Limited genetic increases in Rht3 plant height, up to 70 cm, were achieved by incorporating genes from the extremely tall variety 'April Bearded'. Amongst lines from the higher yielding cross, the dwarfing gene did not reduce grain yield but was associated with an increase in grain number of over 25%. Although Rht3 reduced grain protein content by up to 0.8%, breadmaking quality, as measured by SDS sedimentation values and baking tests, was not affected. A controlled environment experiment with near-isogenic Rht3 and rht3 lines indicated that reduced grain size in the dwarfs is a competitive response to the increase in fertility rather than a primary effect of the dwarfing gene.
RESUMO
The effects of the Tom Thumb dwarfing gene, Rht3, on the quality and quantity of grain α-amylase produced during germination and by induction with exogenous gibberellic acid are described. In a season conducive to high sprouting damage the gene reduced α-amylase levels in the field by 77%. Selection among random Rht3 genotypes showed that other genetic factors can be combined with the dwarfing gene to further increase sprouting damage resistance.
