Semidwarf ( sd-1 ), “green revolution” rice, contains a defective gibberellin 20-oxidase gene

Abstract

The introduction of semidwarf rice (Oryza sativa L.) led to record yield increases throughout Asia in the 1960s. The major semidwarfing allele, sd-1, is still extensively used in modern rice cultivars. The phenotype of sd-1 is consistent with dwarfism that results from a deficiency in gibberellin (GA) plant growth hormones. We propose that the semidwarf (sd-1) phenotype is the result of a deficiency of active GAs in the elongating stem arising from a defective 20-oxidase GA biosynthetic enzyme. Sequence data from the rice genome was combined with previous mapping studies to locate a putative GA 20-oxidase gene (Os20ox2) at the predicted map location of sd-1 on chromosome 1. Two independent sd-1 alleles contained alterations within Os20ox2: a deletion of 280 bp within the coding region of Os20ox2 was predicted to encode a nonfunctional protein in an indica type semidwarf (Doongara), whereas a substitution in an amino acid residue (Leu-266) that is highly conserved among dioxygenases could explain loss of function of Os20ox2 in a japonica semidwarf (Calrose76). The quantification of GAs in elongating stems by GC-MS showed that the initial substrate of GA 20-oxidase activity (GA53) accumulated, whereas the content of the major product (GA20) and of bioactive GA1 was lower in semidwarf compared with tall lines. We propose that the Os20ox2 gene corresponds to the sd-1 locus.

Gibberellin homeostasis and plant height control by EUI and a role for gibberellin in root gravity responses in rice

“…Two approaches can be adopted to lower endogenous GA levels and therefore develop elite varieties; these include decreasing GA biosynthesis and increasing GA catabolism. Indeed, by using the mutant GA biosynthesis gene sd-1, a mutated GA20ox gene [9,10], or by using the GA catabolism gene OsGA2ox1 to manipulate GA levels [14], breeding for semi-dwarf rice is now feasible through molecular design.…”

“…Many GA-related mutants have been isolated from the model plant species Arabidopsis thaliana and rice (Oryza sativa L.), and the majority of the underlying genes have been found to encode enzymes that are related to GA metabolism or components of GA signaling [1][2][3][4][5][6][7]. Many GA mutants show dramatically reduced plant height and hence increased yield potential and lodging resistance of modern cereal varieties, thus greatly contributing to the success of the 'green revolution' [8][9][10]. Recently, GID1 (GIBBERELLIN INSENSITIVE DWARF 1) was identified as a soluble GA receptor in rice and Arabidopsis [11][12][13].…”

“…For example, a mutation in the GA20ox gene (sd-1) resulted in decreased GA levels in rice, which has been attributed to the rice 'green revolution' gene [9,10]. Moreover, ectopic expression of OsGA2ox1 under the control of the promoter of the GA biosynthesis gene GA3ox2 resulted in a semi-dwarf phenotype, suggesting the potential for high yield production in rice [14].…”

Rice DENSE AND ERECT PANICLE 2 is essential for determining panicle outgrowth and elongation

“…So far, numerous QTLs or genes controlling plant architecture have been cloned [2][3][4][5]. In the case of the 'Green Revolution', grain yields have been significantly increased by growing lodging-resistant semi-dwarf varieties of wheat and rice [6,7]. have been reported; EP2 was mapped to chromosome 4, and EP3 encodes a putative F-box protein [15,16].…”

New path towards a better rice architecture

“…One of the popular approaches used by breeders to attain higher yield is to breed plants with ideal plant architecture, leading to the New Plant Type (NPT) concept. Unlike the semi-dwarf plants of the Green Revolution [2,3], NPT plants have less tillers but more grains per panicle coupled with sturdier stems, giving rise to higher yield potential and better lodging resistance.…”