Abstract
Argan trees (Argania spinosa) belong to a species native to southwestern Morocco, playing an important role in the environment and local economy. Argan oil extracted from kernels has a unique composition and properties. Argan trees were introduced in Tunisia, where hundreds of trees can be found nowadays. In this study, we examined reproductive development in Argan trees from four sites in Tunisia and carried out the functional characterization of a floral homeotic gene in this non-model species. Despite the importance of reproductive development, nothing is known about the genetic network controlling flower development in Argania spinosa. Results obtained in several plant species established that floral organ development is mostly controlled by MADS-box genes and, in particular, APETALA3 (AP3) and PISTILLATA (PI) homologs are required for proper petal and stamen identity. Here, we describe the isolation and functional characterization of a MADS-box gene from Argania spinosa. Phylogenetic analyses showed strong homology with PI-like proteins, and the expression of the gene was found to be restricted to the second and third whorls. Functional homology with Arabidopsis PI was demonstrated by the ability of AsPI to confer petal and stamen identity when overexpressed in a pi-1 mutant background. The identification and characterization of this gene support the strong conservation of PI homologs among distant angiosperm plants.
Highlights
We took advantage of the available Argan population in Tunisia to study the diversity of flower disposition and number
The androecium is composed of five stamens forming a ring around the carpel that protrudes before flower opening (Figure 1e)
Season was the main source of variation in the number of glomeruli on Argan shoots, which may explain conflicting reports on flowering times in the literature [36]
Summary
Genetics and molecular studies firmly established that floral organ development is genetically controlled by transcription factors encoded by genes from the MADS-box family [16,17]. Mutations in either of these genes result in similar phenotypes with homeotic transformations of petals into sepals and stamens into carpels [23,24] These two proteins, encoded by AP3 and PI, function as obligate heterodimers to bind DNA and directly regulate different sets of genes at distinct phases of flower development [25]. We examined the floral diversity of a collection of Argan trees from different geographical locations in Tunisia, and second, we isolated a PI-like B-class gene that we show is involved in petal and stamen identity.
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