Genetic diversity and phylogenetic relationship among Tunisian cactus species (Opuntia) as revealed by random amplified microsatellite polymorphism markers.

Opuntia ficus indica is one of the most economically important species in the Cactaceae family. Increased interest in this crop stems from its potential contribution to agricultural diversification, application in the exploitation of marginal lands, and utility as additional income sources for farmers. In Tunisia, O. ficus indica has been affected by drastic genetic erosion resulting from biotic and abiotic stresses. Thus, it is imperative to identify and preserve this germplasm. In this study, we focused on the use of random amplified microsatellite polymorphisms to assess genetic diversity among 25 representatives of Tunisian Opuntia species maintained in the collection of the National Institute of Agronomic Research of Tunisia. Seventy-two DNA markers were screened to discriminate accessions using 16 successful primer combinations. The high percentage of polymorphic band (100%), the resolving power value (5.68), the polymorphic information content (0.94), and the marker index (7.2) demonstrated the efficiency of the primers tested. Therefore, appropriate cluster analysis used in this study illustrated a divergence among the cultivars studied and exhibited continuous variation that occurred independently of geographic origin. O. ficus indica accessions did not cluster separately from the other cactus pear species, indicating that their current taxonomical classifications are not well aligned with their genetic variability or locality of origin.

Top-DER- and Dpp-dependent requirements for the Drosophila fos/kayak gene in follicular epithelium morphogenesis.

The Drosophila fos (Dfos)/kayak gene has been previously identified as a key regulator of epithelial cell morphogenesis during dorsal closure of the embryo and fusion of the adult thorax. We show here that it is also required for two morphogenetic movements of the follicular epithelium during oogenesis. Firstly, it is necessary for the proper posteriorward migration of main body follicle cells during stage 9. Secondly, it controls, from stage 11 onwards, the morphogenetic reorganization of the follicle cells that are committed to secrete the respiratory appendages. We demonstrate that DER pathway activation and a critical level of Dpp/TGFbeta signalling are required to pattern a high level of transcription of Dfos at the anterior and dorsal edges of the two groups of cells that will give rise to the respiratory appendages. In addition, we provide evidence that, within the dorsal-anterior territory, the level of paracrine Dpp/TGFbeta signalling controls the commitment of follicle cells towards either an operculum or an appendage secretion fate. Finally, we show that Dfos is required in follicle cells for the dumping of the nurse cell cytoplasm into the oocyte and the subsequent apoptosis of nurse cells. This suggests that in somatic follicle cells, Dfos controls the expression of one or several factors that are necessary for these processes in underlying germinal nurse cells.