Noly, A.; Faux, C.; Shaldaeva, M.; Bois-Naegelin, L.; Fort, P. P.; Helmlinger, D.

Dynamic patterns of gene gain and loss play a major role in the diversification of eukaryotes. Deep phylogenomic analyses proposed that major evolutionary transitions coincide with increased genome complexity, before various degrees of ecological specialization drive gradual loss of gene families. Here we report a comprehensive analysis of gene gain and loss across the fission yeast clade, which evolutionary trajectory remains elusive. Reductive evolution of metabolic genes is a major contributor to species diversification, as observed in other fungal taxa. Notably, we uncovered an evolutionary scenario in which an ancestral gene duplication was followed by lineage-specific loss of each paralog, except in S. pombe, which retained both. We demonstrate that these paralogs encode catalytically-active invertases, named Inv1 and Inv2, with distinct enzymatic properties, localization, regulation, and physiological roles. Inv1 is a secreted enzyme subject to glucose catabolite repression and is the sole invertase required for sucrose assimilation, resembling canonical yeast invertases. In contrast, Inv2 is intracellular, constitutively expressed, and required for inducing sexual differentiation in response to nutrient availability. Overall, these findings reveal an unexpected role for carbon metabolism in modulating the haploid-diploid cycle of fission yeasts, suggesting that diversification of core metabolic functions may contribute to adaptation to environments with distinct sugar compositions.