| Budget Amount *help |
¥2,400,000 (Direct Cost: ¥2,400,000)
Fiscal Year 2000: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1999: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1998: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1997: ¥700,000 (Direct Cost: ¥700,000)
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| Research Abstract |
The floral morphology of grass species is distinct from typical dicot plants. In order to achieve a better understanding of the molccular basis for this diversion, we isolated RAP1A, RAP1B and RAG, putative rice homologs for the Arabidopsis class A gene APETALA1(AP1) and class C gene AGAMOUS(AG), respectively. Expression patterns of RAP1A.RAG, and OsMADS2, a rice homolog of the class B gene, were analyzed by in situ hybridization. RAP1A mRNA was expressed in the apical region of the floral meristem at an early stage of spikelet development, and then its expression was localized in developing lemma, palea and lodicules. OsMADS2 transcript was first observed in the region where stamen primordia are formed. Soon after, OsMADS2 mRNA appeared in the lodicule primordia as well as stamen primordia and this RNA accumulation pattern persisted till late stages of floral development. The expression of RAG was observed in stamens and pistils of wild type young spikelets. These RNA accumulation pat
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terns are mostly similar to those of Arabidopsis class A, B, C genes supporting the notion that the ABC model may be extended to rice.
In order to clarify the evolutionary relationship between grass sterile organs, such as lodicules, the lemma and the palea, and the dicot floral organs, we expressed RAG, a rice (Oryza sativa L.) AGAMOUS(AG) ortholog, in rice plants under the control of an Actin I promoter.As a consequence of the ectopic expression of the RAG, lodicules were homeotically transformed into stamens. In total, the transformation of lodicules to staminoid organs was observed in 18 out of 26 independent transgenic lines. In contrast to the almost complete transformation occurred in lodicules, none of the transgenic plants exhibited any morphological alterations in the palea or the lemma. Our results confirmed the prediction that the lodicule is an equivalent of a dicot petal and that the ABC model can be applied to rice at least for organ specification in lodicules and stamens. On the other hand, the absence of morphological alterations in the palea or the lemma raised the possibility that the simple application of the ABC model to structures outside the lodicules may not be valid. Less
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