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Flower Morphogenesis

Disciplines Biology
Research fields Plant biology, Transcriptome
Supporting organisms CNRS, ENS de Lyon, INRA, UCBL
Geographical location ENS de Lyon (Campus Charles Mérieux)
Team leader Mohammed Bendahmane

From an economic point of view the flower is important as an ornamental structure and also as the developmental starting point for seed and fruit production. Petal is the major organ determining flower quality, and thus greatly influences the economic value of a wide range of crop and ornamental plants. Work in our group focuses on understanding the molecular events that influence petal morphogenesis using Arabidopsis thaliana as a genetic tool and the rose as an ornamental model species. Our general objective is the identification and functional characterization of genes that are required for the molecular and cellular processes responsible for petal characters such as petal size and shape determination, longevity and number. Identification and analyses of these genes are crucial to understand the molecular mechanisms that lead to petal morphogenesis.

In Arabidopsis thaliana the APETALA1 (AP1), PISTILLATA (PI), APETALA3 (AP3) and the SEPALLATA (SEP) MADS-box transcription factors have been shown to interact to form multimeric protein complexes required to specify petal identity. They presumably regulate a set of downstream structural genes (so called “realizators”) that encode proteins required for the cell division and differentiation events that lead to petal organogenesis. However, very little information is available about the downstream events involved in petal morphogenesis. Our group focuses on the investigation of these downstream events.

  1. We are currently focusing our work on the functional characterisation of BIGPETALp (BPEp), a petal preferentially expressed transcription factor we identified to be involved in limiting petal size by controlling cell expansion in A. thaliana (Szecsi et al., EMBO J 2006). BPEp is one of two transcripts originating from the BIGPETAL gene through an alternative splicing event. The second transcript, BPEub is ubiquitously expressed (Szecsi et al., 2006). Some of the topics under investigation include : (i) Regulation of BPEp expression at the post-transcriptional level (via intron retention; Brioudes et al., Plant J 2009), (ii) Molecular and genetic interaction between BPEp and its interacting proteins: what is the biological significance of these interactions ? (iii) What are the downstream targets involved in the control of cell differentiation in order to generate petals with specific shape and size ?
  2. In plants as in animals, organogenesis and final organ size requires controlled production, coordinated growth and differentiation of new cells. These cellular responses are tightly controlled by environmental and genetic factors. However, conversely to animals, plants continue developing new organs throughout their life. Recently, we investigated the biological function of A. thaliana genes homologous to those known to control organ growth in Drosophila. Within this research programme we are currently using Drosophila and Arabidopsis (Figure 2) as model organisms to investigate the role of selected genes in cell division and expansion regulation and the resulting organ size modifications : eye and wings for Drosophila and petals and leafs in Arabidopsis. Among the genes we are currently studying, the TCTP (encode for the Translationally controlled Tumor Protein) is of particular interest (See our recent publication by Brioudes et al., PNAS 2010)
  3. The final stage of the developmental program, petal senescence, is particularly important as it is has a major influence on the vase life and the quality of ornamental plants. Although a limited number of genes (senescence associated genes or SAGs) have been shown to be expressed during petal senescence, very little information is available concerning their function. In our group, petal senescence work focuses on understanding regulation of few SAG genes that are rapidly and strongly induced early in the senescence and programmed cell death in Arabidopsis leaves and petals.
  4. Petal traits have been heavily selected in a wide range of ornamental plants. Work in our group focuses on identifying genes that influence petal characters such as shape, number, perfume and longevity. We use the rose as ornamental model species and in which we want to understand the effects of domestication in generating petal trait diversity. Analyses of selected genes in botanical roses and in modern roses (Figure 2) are crucial for understanding the molecular mechanisms that lead to petal formation and the processes of flower variation and diversification during rose domestication (Lyon Botanical garden has an exhaustive rose collection). Currently, we are using a combination of candidate gene and transcriptomic approaches to identify the molecular mechanisms that control flower development and petal number per flower in Rosa sp. To validate the function of selected genes we have recently developed a reproducible rose genetic transformation protocol that we are using to study selected genes (Vergne et al., Plant Cell Tiss Organ Cult 2010; Dubois et al., PLoSONE 2010).