1. John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, UK
2. These authors contributed equally to this work
3. Present address: Rice Transformation Laboratory, Centre for Plant Molecular Biology, Tamil Nadu Agricultural University, Coimbatore-641 003, India.

Correspondence to: Nicholas P. Harberd¹ Correspondence and requests for materials should be addressed to N.P.H. (e-mail: Email: harberd@bbsrc.ac.uk).EMBL data library accession numbers are: AJ242530,AJ242531.

Abstract

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'^{1, 2, 3, 4}. The new varieties are shorter, increase grain yield at the expense of straw biomass, and are more resistant to damage by wind and rain³,⁴. 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) loci⁴,⁵. Here we show that Rht-B1/Rht-D1 and maize dwarf-8 (d8)⁶,⁷ are orthologues of the Arabidopsis Gibberellin Insensitive (GAI) gene⁸,⁹. These genes encode proteins that resemble nuclear transcription factors and contain an SH2-like¹⁰ 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.