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Cabo Verde’s flora as source of gene resilience to climate changes and relevant bioactive compounds: a genomic and chemical approach
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Located 570 km west of Dakar, Senegal, Cabo Verde is an African archipelago made of ten volcanic islands, nine of them inhabited, one uninhabited, and various islets. Cabo Verde, described in the first chapter of this thesis, is part of the Macaronesia islands, which are one of the most important ecoregions in the world regarding biodiversity, for its paleo and neoendemisms.
The long biogeographic isolation of the archipelago has led to a unique evolution of taxa and associations of flora, as local species gradually adapted to climatic and geological conditions, and the further fragmentation of the territory into different islands, with different characteristics and sizes, amplified the effect of biogeographic isolation. Cabo Verde’s flora is thus characterized by low richness in terms of the total number of species, but a high number of endemic taxa. Cabo Verde is extremely vulnerable to climate change and exposed to increasingly extreme weather events, namely, desertification of land and persistent droughts, occasional but severe and highly damaging heavy rains. Seventy eight percent of Cabo Verde's endemic flora is threatened.
The second chapter presents West Africa as one of the most biodiverse regions on the planet. Major
threats to plant diversity in the region include population growth, agriculture expansion, deforestation, invasive alien species, climate change, overexploitation, and overall anthropogenic interventions along with natural catastrophe. Cabo Verde, among West African countries, has the smallest land area and number of species, however, is the second country in the region with the highest number of endemic species, making any of those species' extinction a world-level loss. This thesis highlights Cabo Verde as one of the countries in West Africa that managed to increase its forest area the most from 1990 to 2016. The country also succeeded in increasing the number and coverage of its land PA and has ratified most of the international arrangements regarding biodiversity conservation. Cabo Verde is, thus, an example to follow in Africa when it comes to natural floristic resources conservation and management.
The third chapter is focused on the use of floristic diversity as a source of food, providing a report of the status and trends of agriculture in Cabo Verde, as well as state the crucial role of legume species in promoting sustainable agriculture in the country, and as an important ally in the fight against food insecurity. Results show that, among the ten Cabo Verde Islands, Santiago has the largest area used for agriculture (52.5%), and that rainfed farming is the most predominant in the country. Fifteen species are used as food and five of them are locally traded (Cajanus cajan,
Lablab purpureus, Phaseolus lunatus, Phaseolus vulgaris, and Vigna unguiculata). The role of these species as sources of important minerals, antioxidants, and nutritional components for food security is highlighted, and the native ones (Lablab purpureus and Vigna unguiculata) stand-out as particularly well-adapted to the climate of these islands, which are already experiencing the adverse effects of climate change. The prolonged drought periods, exposure, erosion, and soil degradation, which led to increasing desertification over the last decades, have been identified as the main constraints to agrarian development across the ten islands of the archipelago.
Chapters four, five and six focus on the use of plants as sources of therapeutical bioactive ingredients and to value native and endemic plants used in traditional medicine. Through these studies it was possible to present an assessment aimed to evaluate the medicinal uses and pharmacological potential of some of those plants occurring in Santiago Island. Artemisia gorgonum, Tamarix senegalensis, and Sideroxylon marginatum were selected for estimation of their in vitro antioxidant, antimicrobial and the two latter species were also assessed for their antidiabetic activities. Ethanolic extracts were richer in phenolic compounds and more active than their aqueous counterparts. All the studied extracts revealed significant in vitro antioxidant
properties. As to both ethanolic extracts and infusion preparations, showed that T. senegalensis was the most efficient in inhibiting the growth of Gram-negative and Gram-positive clinical isolated and food-contaminant bacteria. Regarding the antifungal potential of these plants, the ethanolic extract of A. gorgonum and S. marginatum were the most efficient in inhibiting the growth of the selected fungi. The results suggest that extracts of T. senegalensis, and S. marginatum can delay glucose absorption, thereby helping to slow down the progression of diabetes. A. gorgonum proved to be the most effective in inhibiting tumor growth (CaCo).
Regarding anti-plasmodial activity, A. gorgonum and aqueous extract of T. senegalensis exhibited high antiplasmodial activity without cytotoxicity. These results will help to raise awareness about the need for sustainable use and conservation of native flora, especially medicinal tree species traded in local markets.
Finally, the seventh chapter talks about endemic Cabo Verde Diplotaxis taxa, the greatest known radiation for this species, which are Crop Wild Relatives (CWR) from the Brassicacea family, extremely well adapted to various types of abiotic and biotic stresses. In this chapter we also investigated the diversity and divergence of the gene clusters involved on the biosynthesis of Glucosinolates (GLS), secondary metabolites produced by Brassicacea, and are linked to abiotic
stress resistance. Chemical diversity assessment allowed recognizing that Brassica and Diplotaxis have distinct GLS chemo-profiles, highlighting that the latter genus includes extremely GLS-rich species. Regarding nuclear ITS, Cabo Verde endemic Diplotaxis appear to have a common ancestor, which underwent subsequent radiation, and form a monophyletic group in the Brassicaceae ITS phylogenetic tree. These endemic species from Cabo Verde, can be, thus, a good source of resilience genes for economically important crops.
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Gene resilience Climate changes CaboVerde