Evolutionary genetics of lactase persistence in Eurasian human populations

Although ability to digest lactose generally declines after weaning in all mammals, in some human populations it persists also in adult individuals, a condition named lactase persistence (LP). Studies on the prevalence of the LP phenotype in worldwide human populations have shown that the frequency of this trait is highly variable in different ethnic groups, appearing to be positively correlated with the importance of milk in the diet. In particular, several single-nucleotide polymorphisms (SNPs) in the proximity of the LCT gene have been proved to be associated with LP. Nevertheless, few studies have till now analyzed genetic variation underlying LP in a wide set of Eurasian populations and, especially, in the Italian one. In the present study, we thus typed 40 SNPs surrounding the LCT gene in more than 1,000 samples from Italian and Arabic peninsulas to investigate patterns of LP-related genetic diversity in two regions which have played a pivotal role in the recent human evolutionary history according to their geographical position and historical/archaeological records. Our results underline a high and complex variability of the explored genomic region in both studied populations. In particular, a clear diversification of Northern Italian groups from the rest of the peninsula, was observed, with the formers being genetically more similar to Northern European populations than to Southern Italians. These observation are consistent with known decreasing pattern of LP from Northern to Southern Italy and suggest the possibility of an independent evolution of LP-associated genotypes in Northern Italy. A similar scenario was observed in the Arabian peninsula, with Dhofari Arabs from Southern Oman and Yemeni clustering together with respect to Arabs from Northern Oman and the subgroup of Omanis of Asian origin which appeared instead to be genetically closer to Europeans than to the rest of Arabic groups.

Identification and genetic diversity in phytoplasmas associated with diseases of cassava and other agronomic relevant crops in south-east Asia and Latin America

Identification and genetic diversity of phytoplasmas infecting tropical plant species, selected among those most agronomically relevant in South-east Asia and Latin America were studied. Correlation between evolutionary divergence of relevant phytoplasma strains and their geographic distribution by comparison on homologous genes of phytoplasma strains detected in the same or related plant species in other geographical areas worldwide was achieved. Molecular diversity was studied on genes coding ribosomal proteins, groEL, tuf and amp besides phytoplasma 16S rRNA. Selected samples infected by phytoplasmas belonging to diverse ribosomal groups were also studied by in silico RFLP followed by phylogenetic analyses. Moreover a partial genome annotation of a ‘Ca. P. brasiliense’ strain was done towards future application for epidemiological studies. Phytoplasma presence in cassava showing frog skin (CFSD) and witches’ broom (CWB) diseases in Costa Rica - Paraguay and in Vietnam – Thailand, respectively, was evaluated. In both cases, the diseases were associated with phytoplasmas related to aster yellows, apple proliferation and “stolbur” groups, while only phytoplasma related to X-disease group in CFSD, and to hibiscus witches’ broom, elm yellows and clover proliferation groups in CWB. Variability was found among strains belonging to the same ribosomal group but having different geographic origin and associated with different disease. Additionally, a dodder transmission assay to elucidate the role of phytoplasmas in CWB disease was carried out, and resulted in typical phytoplasma symptoms in periwinkle plants associated with the presence of aster yellows-related strains. Lethal wilt disease, a severe disease of oil palm in Colombia that is spreading throughout South America was also studied. Phytoplasmas were detected in symptomatic oil palm and identified as ‘Ca. P. asteris’, ribosomal subgroup 16SrI-B, and were distinguished from other aster yellows phytoplasmas used as reference strains; in particular, from an aster yellows strain infecting corn in the same country.