Molecular characterization of Rht-1 dwarfing genes in hexaploid wheat.
The introduction of the Reduced height (Rht)-B1b and Rht-D1b semidwarfing genes led to impressive increases in wheat (Triticum aestivum) yields during the Green Revolution. The reduction in stem elongation in varieties containing these alleles is caused by a limited response to the phytohormone gibberellin (GA), resulting in improved resistance to stem lodging and yield benefits through an increase in grain number. Rht-B1 and Rht-D1 encode DELLA proteins, which act to repress GA-responsive growth, and their mutant alleles Rht-B1b and Rht-D1b are thought to confer dwarfism by producing more active forms of these growth repressors. While no semidwarfing alleles of Rht-A1 have been identified, we show that this gene is expressed at comparable levels to the other homeologs and represents a potential target for producing novel dwarfing alleles. In this study, we have characterized additional dwarfing mutations in Rht-B1 and Rht-D1. We show that the severe dwarfism conferred by Rht-B1c is caused by an intragenic insertion, which results in an in-frame 90-bp insertion in the transcript and a predicted 30-amino acid insertion within the highly conserved amino-terminal DELLA domain. In contrast, the extreme dwarfism of Rht-D1c is due to overexpression of the semidwarfing Rht-D1b allele, caused by an increase in gene copy number. We show also that the semidwarfing alleles Rht-B1d and Rht-B1e introduce premature stop codons within the amino-terminal coding region. Yeast two-hybrid assays indicate that these newly characterized mutations in Rht-B1 and Rht-D1 confer "GA-insensitive" dwarfism by producing DELLA proteins that do not bind the GA receptor GA INSENSITIVE DWARF1, potentially compromising their targeted degradation.
Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK.
Stephen
S
Pearce
Robert
R
Saville
Simon P
SP
Vaughan
Peter M
PM
Chandler
Edward P
EP
Wilhelm
Caroline A
CA
Sparks
Nadia
N
Al-Kaff
Andrey
A
Korolev
Margaret I
MI
Boulton
Andrew L
AL
Phillips
Peter
P
Hedden
Paul
P
Nicholson
Stephen G
SG
Thomas
D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D005875:Gibberellins / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D010937:Plant Growth Regulators / Q000494:pharmacology*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018547:Plant Stems / Q000235:genetics / Q000254:growth & development; D011123:Polyploidy; D012333:RNA, Messenger / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D014908:Triticum / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D020798:Two-Hybrid System Techniques
D018744:DNA, Plant; D005875:Gibberellins; D010937:Plant Growth Regulators; D010940:Plant Proteins; C120413:RHT-D1A protein, Triticum aestivum; D012333:RNA, Messenger; D018749:RNA, Plant