The rice semidwarf-1 (sd1) gene is well known as the "green revolution gene" and controls the plant height of rice.
This gene is originally derived from the Chinese cultivar Dee-Geo-Woo-Gen (DGWG). It encodes an oxidase enzyme involved in the biosynthesis of gibberellin, which is a plant growth hormone. The rice genome carries at least two GA20ox genes (GA20ox-1 and GA20ox-2). SD1 corresponds to GA20ox-2. Mutation of SD1 will cause a semi-dwarf phenotype of rice without seed yield being affected . It is not surprising that a rice semidwarfing gene encodes GA20-ox since successful production of semidwarf plants using antisense or overexpressed GA20-ox genes has been reported in Arabidopsis, Solanum dulcamara, potato, and lettuce .
It is a key enzyme in the biosynthesis of gibberellin that catalyses the three steps GA53->GA44->GA19->GA20. Impaired GA 20-oxidase activity will cause elevated content of GA53, and reduced amount of G20. However, there is slight difference between different strains. The extent of GA1 is lower in Doongara (semi-dwarf rice strain) when compared with Kyeema (tall), while there is no significant difference between Calrose76 (semi-dwarf rice strain) and Calrose (tall). Calrose76 has lower contents of GA44 and of GA19 than Calrose, while there is no significant difference between Doongara (semi-dwarf rice strain) and Kyeema (tall) .
'Dee-Geo-Woo-Gen' (semi-dwarf rice strain): A 383-base-pair deletion from the genome (A 280-bp deletion within the coding region), which induces a frameshift that creates a stop codon in SD1, may be related with the semi-dwarf phenotype .
Calrose76 (semi-dwarf rice strain): The DNA sequence of Calrose76 is identical to Calrose (tall) except for a C to T transition at position 798 that resulted in a change of the predicted amino acid leucine (Leu-266) in Calrose to phenylalanine in Calrose76 .
It has been found that introgression of a chromosomal block containing the SD1 allele from tropical japonica is associated with a change in growth patterns in BHA1 (one weedy rice population) .
This gene is strongly expressed in the leaf blade, stem and unopened flower, whereas GA20ox-1 is predominantly expressed in the unopened flower .
Among the DGWG-type sd-1 mutants, IR24 and Habataki have little transcript of this gene, while Milyang 23 expresses a normal or greater amount of truncated transcript. No significant difference is observed between Calrose and its single-nucleotide-substitution mutant Calrose 76 .
Analysis of the tissue- and stage-specificity of transcription of sd1 in Nipponbare revealed that this gene was expressed within 48 hr after sowing, as well as in 10-day-old plants, 30-day-old leaves, and flowering panicles; no transcription is detected in 24-hr-old seedlings or in 14-day-old roots. Transcript accumulates predominantly in adult leaves .
|Primer||Forward primer||Reverse primer|
|Gene amplication||5'-CAACTCACTCCCGCTCAACACAGC-3'||5'-TTTGAAATGCAATGTCGTCCACC-3' (used to amplify exon 1 )|
|5'-GCGCCAATGGGGTAATTAAAACG-3'||5'-GGCATTCCATTGTTTGTGATTGG-3' (used to amplify exon 2 )|
|5'-GTTTGTCCTTGTCGCGTTGCTCAG-3'||5'-TCTGTTCGTTCCGTTTCGTTCCG-3' (used to amplify exon 3 )|
Except sd1, another ‘green revolution’ gene named Rht1, which encodes a GA signal suppressor DELLA protein. The deletion in the N-terminal region of the native RHT1 constitutively suppresses GA signaling, consequently resulting in a dominant semi-dwarf phenotype . Both sd1 and Rht1 are associated with GA pathway, indicating the importance of GA in the regulation of developmental processes and making it a prime target for improving crop yield .
The wheat green-revolution gene Rht (for ‘reduced height’)  is a gain-of-function allele caused by a mutation in a transcription factor that is associated with the gibberellin signalling pathway. As wheat has a hexaploid genome, it does not contain recessive alleles such as sd1 in rice that might otherwise be used to produce a semi-dwarf strain of wheat. Although the genetic and biochemical functions of the rice SD1 and wheat RHT proteins are completely different (that is, recessive versus dominant, loss-of-function versus gain-offunction events, enzyme versus transcription factor, respectively), the products of both genes are linked with gibberellin malfunction .
In rice, Slr1 gene encodes the DELLA protein. Three semi-dominant dwarf mutants (Slr1-d1, Slr1-d2 and Slr1-d3) associated with this gene have been identified, which were caused by gain-of-function mutations in the N-terminal region of SLR1. These three mutants are responsive to GA at a reduced rate, with later SLRl degradation, and showing reduced interaction activity with GID1 (GA receptor) comparing with wild type rice .
Labs working on this gene
- Bioscience Center, and Graduate School of Bioagricultural Science, Nagoya University, Nagoya 464-8601, Japan
- Honda R&D, Wako Research Center, Wako 351-0193, Japan
- International Rice Research Institute, Manila, DAPO Box 7777, Philippines
- BioResources Center, and Plant Molecular Biology Laboratory, Riken, Tsukuba 305-0074, Japan
- Division of Plant Industry, Commonwealth Scientific and Industrial Research Organization, GPO Box 1600, Canberra ACT 2601, Australia
- Plant Genome Center, 1-25-2 Kannondai, Tsukuba, Ibaraki 305-0856, Japan
- Monna L, Kitazawa N, Yoshino R, Suzuki J, Masuda H, et al. (2002) Positional cloning of rice semidwarfing gene, sd-1: rice "green revolution gene" encodes a mutant enzyme involved in gibberellin synthesis. DNA Res 9: 11-17.
- Sasaki A, Ashikari M, Ueguchi-Tanaka M, Itoh H, Nishimura A, et al. (2002) Green revolution: a mutant gibberellin-synthesis gene in rice. Nature 416: 701-702.
- Spielmeyer W, Ellis MH, Chandler PM (2002) Semidwarf (sd-1), "green revolution" rice, contains a defective gibberellin 20-oxidase gene. Proc Natl Acad Sci U S A 99: 9043-9048.
- Reagon M, Thurber CS, Olsen KM, Jia Y, Caicedo AL (2011) The long and the short of it: SD1 polymorphism and the evolution of growth trait divergence in U.S. weedy rice. Mol Ecol 20: 3743-3756.
- Hedden P. (2003) The genes of the Green Revolution. Trends Genet 19: 5-9.
- Peng J, Richards DE, Hartley NM, Murphy GP, Devos KM, et al. (1999) 'Green revolution' genes encode mutant gibberellin response modulators. Nature 400: 256-261.
- Asano K, Hirano K, Ueguchi-Tanaka M, Angeles-Shim RB, Komura T, et al. (2009) Isolation and characterization of dominant dwarf mutants, Slr1-d, in rice. Mol Genet Genomics 281: 223-231.