Abstract
C-function MADS-box transcription factors belong to the AGAMOUS (AG) lineage and specify both stamen and carpel identity and floral meristem determinacy. In core eudicots, the AG lineage is further divided into two branches, the euAG and PLE lineages. Functional analyses across flowering plants strongly support the idea that duplicated AG lineage genes have different degrees of subfunctionalization of the C-function. The legume Medicago truncatula contains three C-lineage genes in its genome: two euAG genes (MtAGa and MtAGb) and one PLENA-like gene (MtSHP). This species is therefore a good experimental system to study the effects of gene duplication within the AG subfamily. We have studied the respective functions of each euAG genes in M. truncatula employing expression analyses and reverse genetic approaches. Our results show that the M. truncatula euAG- and PLENA-like genes are an example of subfunctionalization as a result of a change in expression pattern. MtAGa and MtAGb are the only genes showing a full C-function activity, concomitant with their ancestral expression profile, early in the floral meristem, and in the third and fourth floral whorls during floral development. In contrast, MtSHP expression appears late during floral development suggesting it does not contribute significantly to the C-function. Furthermore, the redundant MtAGa and MtAGb paralogs have been retained which provides the overall dosage required to specify the C-function in M. truncatula.
Highlights
Genetic regulation of flower development has been subject of study over the last decades, in the model species Arabidopsis thaliana and Antirrhinum majus
To identify MADS-box genes involved in flower development, we screened a cDNA library of M. truncatula floral apices using a set of MADS-box fragments from different species as a probe [48,49]
We developed transgenic M. truncatula lines in which MtAG genes were down regulated by RNA interference (RNAi) and three independent lines were obtained
Summary
Genetic regulation of flower development has been subject of study over the last decades, in the model species Arabidopsis thaliana and Antirrhinum majus. These studies provided a general understanding of floral organ development in higher plants and led to the proposal of the ABCDE model, which postulates that floral organ identity in each whorl is defined by five functions named A, B, C, D and E (for review [1,2,3,4]). Studies of MADS-box genes in higher eudicotyledoneous flowering plants show that they are key regulators of flower development. Additional C-function genes have been identified: SHATTERPROOF1 (SHP1) and SHATTERPROOF2 (SHP2) [9,10] genes in Arabidopsis and FARINELLI (FAR) [11] in Antirrhinum
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