Loss-of-function of a Rice Gibberellin Biosynthetic Gene, GA20 oxidase (GA20ox-2), Led to the Rice 'Green Revolution'.

Abstract

A rice semi-dwarf variety, IR8, known as "miracle rice" enabled dramatic increases rice production and its widespread adoption averted predicted food shortages in Asia during the 1960s to 1990s. This remarkable achievement was referred to as "green revolution". The short stature of IR8 was derived from the semi-dwarf gene, sd1, and the sd1 gene contributed significantly to the rice "green revolution". In this paper, we described the physiological, molecular genetic and biochemical characterization of the sd1 gene. The sd1 mutant contained lower gibberellin (GA) levels than wild-type plants but responded sensitively to exogenous GA. Cloning and sequence analyses revealed that the SD1 gene encoded a GA biosynthetic enzyme, GA20 oxidase. In all of the sd1 mutants tested, nucleotide deletions or substitutions were observed in the GA20 oxidase gene (GA20ox-2), which induced an internal stop codon or single amino acid substitutions, respectively. The sd1 plants, which the wild-type GA20ox-2 gene was introduced showed the normal height. A recombinant GA20ox-2 protein produced from the cDNA clone in E. coli catalyzed the conversion of GA 53 to GA 20 . These results confirmed that SD1 encodes an active GA20 oxidase. The expression of GA20ox-2 was down-regulated by GA in a similar manner to that of some GA20oxs in other plants. The rice genome carried at least two GA 20-oxidase genes (GA20ox-1 and GA20ox-2) and SD1 corresponded to GA20ox-2, which is highly expressed in the leaves and flowers, whereas GA20ox-1 is preferentially expressed in the flowers. The reduced plant height associated with the sd1 alleles was due to the low amount of active GA in leaves, which was caused by a mutation of the GA20ox-2 gene. On the basis of these results, we discussed the importance of GA in the regulation of plant height in crop breeding.

EFFECTS OF BLUE LIGHT AND PACLOBUTRAZOL ON SEED GERMINATION, VEGETATIVE GROWTH AND YIELD OF BLACK RICE (Oryza sativa L. 'Cempo Ireng')

“…In arabidopsis, application of uniconazole, which is also a gibberellins inhibitor, caused shoot stunting, but with enhanced elongation of the primary roots (Bidadi et al 2009). In semidwarf rice (sd1) obtained from a mutation of the GA20ox-2 gene, the level of endogenous gibberellin was low, however, the normal height of the semidwarf rice is restored by exogenous application of GA (Ashikari et al 2002;Sasaki et al 2002). This gene is expressed mainly in stems and is an important regulatory step on the pathway to synthesize active GA (reviewed in Hedden 2003).…”

Gibberellin Regulates Pollen Viability and Pollen Tube Growth in Rice

“…As mentioned above, rice knockout mutants in genes encoding enzymes that catalyze early steps in the GA synthesis pathway (Os cps1, ks1, ko2, and kao) show severe defects in flower and seed development, whereas those catalyzing later steps (sd1 and d18) show normal flower and seed development (Itoh et al, 2001;Ashikari et al, 2002;Sasaki et al, 2002. Thus, we focused on expression analysis of four of the genes that encode early enzymes in the pathway: CPS1, KS1, KO2, and KAO.…”

Genetic variations in dry matter production and physiological nitrogen use efficiency in rice (<i>Oryza sativa</i> L.) varieties

“…Hokuriku 143 was developed in Japan as a non-shattering mutant line from a Chinese semi-dwarf variety, Nan-jing 11 (Fukuta et al 1994). These semi-dwarf varieties were developed and released as a new ideotype in many countries in tropical and temperate irrigated regions from 1966 to 1990 (Khush 1999, Ashikari et al 2002, Peng et al 2008) and contributed to increased rice yields. Mahsuri is cultivated over wide areas in tropical countries.…”