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Gibberellin 2-oxidases (GA2oxs) regulate plant growth by inactivating endogenous bioactive gibberellins (GAs). Two classes of GA2oxs inactivate GAs through 2Β-hydroxylation: a larger class of C19 GA2oxs and a smaller class of C20 GA2oxs. In this study, we show that members of the rice (Oryza sativa) GA2ox family are differentially regulated and act in concert or individually to control GA levels during flowering, tillering, and seed germination. Using mutant and transgenic analysis, C20 GA2oxs were shown to play pleiotropic roles regulating rice growth and architecture. In particular, rice overexpressing these GA2oxs exhibited early and increased tillering and adventitious root growth. GA negatively regulated expression of two transcription factors, O. sativa homeobox 1 and TEOSINTE BRANCHED1, which control meristem initiation and axillary bud outgrowth, respectively, and that in turn inhibited tillering. One of three conserved motifs unique to the C20 GA2oxs (motif Ill) was found to be important for activity of these GA2oxs. Moreover, C20 GA2oxs were found to cause less severe GA-defective phenotypes than C19 GA2oxs. Our studies demonstrate that improvements in plant architecture, such as semidwarfism, increased root systems and higher tiller numbers, could be induced by overexpression of wild-type or modified C20 GA2oxs. [ABSTRACT FROM AUTHOR]

Abstract??Using transfer DNA (T-DNA) with functions of gene trap and gene knockout and activation tagging, a mutant population containing 55,000 lines was generated. Approximately 81% of this population carries 1?2 T-DNA copies per line, and the retrotransposonTos17was mostly inactive in this population during tissue culture. A total of 11,992 flanking sequence tags (FSTs) have been obtained and assigned to the rice genome. T-DNA was preferentially (?80%) integrated into genic regions. A total of 19,000 FSTs pooled from this and another T-DNA tagged population were analyzed and compared with 18,000 FSTs from aTos17tagged population. There was difference in preference for integrations into genic, coding, and flanking regions, as well as repetitive sequences and centromeric regions, between T-DNA andTos17; however, T-DNA integration was more evenly distributed in the rice genome thanTos17. Our T-DNA contains an enhancer octamer next to the left border, expression of genes within genetics distances of 12.5?kb was enhanced. For example, the normal height of a severe dwarf mutant, with its gibberellin 2-oxidase (GA2ox) gene being activated by T-DNA, was restored upon GA treatment, indicating GA2ox was one of the key enzymes regulating the endogenous level of GA. Our T-DNA also contains a promoterless GUS gene next to the right border. GUS activity screening facilitated identification of genes responsive to various stresses and those regulated temporally and spatially in large scale with high frequency. Our mutant population offers a highly valuable resource for high throughput rice functional analyses using both forward and reverse genetic approaches. [ABSTRACT FROM AUTHOR]