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

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

Floral homeotic mutants

Floral homeotic mutants of Lilium reiterated way. The emergence of this phenotype could also involve AG interactors that normally activate its expression, such as WUSCHEL (WUS) or LEAFY (LFY). Failure of normal expression of such genes in the floral meristem would lead to abnormal AG expression, and consequently to the aberrant floral phenotype (Roeder and Yanofsky, 2001). Similar agamous homeotic changes were found in lily flowers (Figures 1d, 2b), showing both floral homeotic changes and loss of floral determinacy, indicating that the C function is conserved in Liliaceae species and that probably the same gene is, ultimately, dictating both characteristics, the stamen and carpel identities, and the floral determinacy. A wild-type B double flower C festiva Figure 2. Diagram representation of lily floral phenotypes. (A) Wild-type flower, with tepals in its two outer whorls, stamens in the third whorl (circles) and a carpel in the inner whorl (crossed circle in the centre). (B) Double flower with tepals replacing every floral organ in a reiterated manner. (C) festiva phenotype, showing replacement of stamens by tepals and keeping its carpel identity. The novel lily phenotype challenges the ABCDE model Due to the overlapping feature of the ABCDE model, any loss in a given function of the model results in homeotic changes in organs of two adjacent whorls (except for the D and E functions). Whereas the wild-type lily flower presents the pattern [tepals-tepals-stamens-carpel], from outer to innermost positions, the loss of function of an A-type gene would give the pattern [carpels-stamens-stamens-carpel], the lack of a B function would lead to [sepals-sepals-carpels-carpel], mutation in the C function would be noticed by the reiterated pattern [tepals-tepals-tepals-new flower], 84

as visualised in double flowers. Chapter 6 Many studies on the genetics of flower development have been carried out in Arabidopsis and other model species creating an extensive catalogue of homeotic mutants, showing wide allelic series of floral homeotic genes in many cases. Strikingly, we found a novel homeotic mutant phenotype in lily flower that has not been reported in other species. The phenotype, with normal tepals in the first two whorls, presents a complete homeotic conversion of its stamens into tepals, as it is seen in the agamous-like mutant, but shows a completely normal carpel development in its innermost whorl, differing from the C-type loss of function. We called this phenotype festiva (from the Latin, "joyful, pretty") (Figure 1 and 2). This phenotype is interesting commercially not only for having more tepals, but also for not producing pollen, since in mature stages of wild-type flowers it speckles tepals, clothes and the furniture. Many consumers remove the lily anthers prior to display, in order to avoid pollen flecking. Phenotypes such as festiva are, therefore, of great interest to breeding programs, and unravelling the molecular mechanisms behind this phenotype may lead to the development of molecular tools that facilitate replacing stamens by tepals. Unfortunately, we were not able to perform molecular analysis of the festiva genotype in the time frame established to generate this thesis, but instead, we tried here to draw some hypotheses that can be explored later, raising some fascinating perspectives for further investigation. Hypotheses regarding the festiva phenotype The phenotype shown by festiva can, with its perfect homeotic changes of stamens into tepals, be easily pictured as an extension of an A-type function towards the third whorl, to the detriment of the C-type function in this whorl. The challenge, however, is in understanding the exact mechanism through which this function replacement originated. We speculate that the whorl-specific homeotic change seen in festiva can be due to modifications of regulatory elements of A or C genes or to a third whorl-specific factor acting in stamen development. 85

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