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Flower development of Lilium longiflorum - The Lilium information ...

Flower development of Lilium longiflorum - The Lilium information ...

Chapter 8 interaction

Chapter 8 interaction patterns (within the species itself and even beyond the monocot class) and differences in gene promoter activity of transcription factors. On the other hand, molecular breeders can take advantage of the knowledge acquired on lily flower genetics and attempt to manipulate its floral morphology and flowering time, in order to generate novel and commercially interesting phenotypes. B D A C E Se Pe St Ca Ov General Model AP1+AP2 AP3+PI AG SEP3 Arabidopsis AGL 11 Se Pe St Ca Ov LMADS1 + ? ? LLSEP3 LLAG1 LMADS 2 Te Te St Ca Ov Lilium longiflorum Figure 1. The ABCDE model for flower development. The current model states that five genetic functions act in an overlapping fashion in order to trigger the development of floral organs. Genes of each function were found in the model species Arabidopsis. In Lilium longiflorum, some of the ABCDE functions were already characterized. This thesis presents the characterization of LLAG1 and LLSEP3 genes, showing C and E functions, respectively. Heterologous system for functional characterisation of lily genes Given the methodological difficulties encountered in lily to genetic studies of flower morphology in a homologous system, such as its recalcitrance to genetic transformation and a long vegetative phase, we approached the functional characterisation of lily floral genes in a heterologous system, using the model species Arabidopsis thaliana. Despite the easy manipulation of this model species, we met some obstacles during the characterization of LLAG1, which are described in the chapter four of this thesis. Notwithstanding, the use of Arabidopsis as a heterologous system in flower development is not discouraged when the homologous system is not available or presents inconveniences. Given the evolutionary conservation of the ABCDE model and the extensive studies in flower development carried on in Arabidopsis, this species 120

Epilogue is an appropriate system allowing (or speeding up) heterologous functional characterisation of floral genes. Transformation system for lily In our efforts to genetically transform lily, described in chapter five, we were able to generate three transgenic lily clones that were resistant to bialaphos in in vitro conditions via particle bombardment. This transformation method has proven to be of low efficiency in lily and the current trend is towards Agrobacterium systems (Mercuri et al., 2003). However, our preliminary results indicated that this system is also recalcitrant and considerable input is still needed to increase its applicability in lily species. The low number of transgenic clones recovered in the work reported in this chapter did not allow us to reach further goals, such as characterising the activity of a transcription factor and of a gene promoter from dicot species in lily. Nevertheless, given the recalcitrance of lily to transformation, obtaining three transgenic clones out of a single experiment is already a remarkable result. We conclude, based on this work and on our further experience, that lily transformation is feasible, although the particle bombardment protocols currently available do not always provide us with reproducible transformation rates. Nevertheless, we suggest more investigation into methods based on Agrobacterium, since a consistent transformation method is already available for other Liliaceae species, such as onion and shallots (Zheng et al., 2001). Novel floral mutants of lily and new challenges Two types of homeotic floral mutants were found in lily during our studies. Some double flowers, i.e. agamous-like homeotic lily mutants, are commercially available and the correlated phenotype is found in several species. It is clear that it involves the C function of the ABCDE model (Roeder and Yanofsky, 2001), due to its coupled abnormalities (homeotic mutation and loss of floral determinacy). It would be very interesting to investigate at what level this function is misregulated. It is possible that the LLAG1 gene is involved in the process, since it showed a C function when expressed in Arabidopsis (chapter two). We also speculated about a novel homeotic floral phenotype found in lily and never observed in other species, which challenges the current ABCDE model because it presents a homeotic change in only one whorl. In this conceptual chapter, we raised 121

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