MOLECULAR CONTROL OF REPRODUCTIVE ORGAN DEVELOPMENT IN RICE (ORYZA SATIVA L.)

Abstract

Several articles published in literature show that the genes belonging to the MADS-box transcription factors family play important roles during flower development. In particular the genes belonging to the AGAMOUS subfamily, are involved in the development of stamens, carpels, and ovules but also have a function in floral meristem determinacy. Despite the extensive knowledge that has become available about these MADS domain transcription factors in the model plant Arabidopsis thaliana, little was known about these genes in rice (Oryza sativa L.), a model species for monocots. In rice, the AGAMOUS subfamily, recently studied in detail, is composed of the genes OsMADS3 and OsMADS58, phylogenetically placed in the AG-lineage, and OsMADS13 and OsMADS21, belonging to the STK-lineage. Therefore, we decided to investigate the functional conservation of these genes between Arabidopsis thaliana and rice, two species that are quite distant from an evolutionary point of view. First, we performed in situ hybridization experiments and found that OsMADS3 and OsMADS58 displayed an expression pattern very similar to AGAMOUS. Then, we started to analyse single and higher order knock-out and knock-down mutants of osmads3 and osmads58, and found different phenotypic alteration affecting reproductive organs. In the osmads3 mutant the formation of stamens and carpel is partially affected, whereas in the osmads58 single mutant we didn’t find any visible alteration in the morphology of the flower. When we investigated the osmads3 osmads58 double mutant, we observed a severer phenotype than the osmads3 single mutants indicating a certain level of redundancy between these genes. The identity of the third and fourth whorls was completely lost, and stamens and carpels were replaced, respectively, by lodicule and ectopic palea-like structures. In addition, in the osmads3 osmads58 double mutant the floral meristem was indeterminate. Recently, it was shown that the rice STK-lineage gene OsMADS13 also plays a role in meristem determinacy (Dreni et al., 2007). To test the functionally redundancy of AGAMOUS subfamily genes in floral meristem determinacy, we crossed osmads13 with osmads3 and osmads58 to obtain the double mutants. In both cases we observed a complete loss of floral meristem determinacy. We also generated and analysed the triple mutant osmads3 omads13 osmads58, in which we found an increased development of the palea-like organ which develops in place of the carpel. OsMADS13 is specifically expressed in the ovary during all developmental stages, and the single mutant is female sterile because the ovules are converted into carpelloid structures, moreover as mentioned above the floral meristem is partially indeterminate (Dreni et al., 2007). From these results obtained in this first part of my PhD project we concluded that OsMADS3, OsMADS58 and OsMADS13 redundantly control floral meristem determinacy, and that OsMADS3 and OsMADS58 are essential for the development of stamens and carpel in rice. In conclusion we confirmed our…