Ultraviolet-B (UVB) radiation damages plants and decreases their growth and productivity.We previously demonstrated that UVB sensitivity varies widely among Asian rice (Oryza sativa L.) cultivars and that the activity of cyclobutane pyrimidine dimer (CPD) photolyase, which repairs UVB-induced CPDs, determines UVB sensitivity. Unlike Asian rice, African rice (Oryza glaberrima Steud. and Oryza barthii A. Chev.) has mechanisms to adapt to African climates and to protect itself against biotic and abiotic stresses. However, information about the UVB sensitivity of African rice species is largely absent. We showed that most of the African rice cultivars examined in this study were UVB-hypersensitive or even UVB-super-hypersensitive in comparison with the UVB sensitivity of Asian O. sativa cultivars. The difference in UVB resistance correlated with the total CPD photolyase activity, which was determined by its activity and its cellular content. The UVB-super-hypersensitive cultivars had low enzyme activity caused by newly identified polymorphisms and low cellular CPD photolyase contents. The new polymorphisms were only found in cultivars from West Africa, particularly in those from countries believed to be centres of O. glaberrima domestication. This study provides new tools for improving both Asian and African rice productivity.Plants use sunlight for photosynthesis and are therefore exposed to ultraviolet-B (UVB) radiation (280-315 nm). Damage caused by UVB radiation decreases plant growth and productivity 1 . Artificial UVB radiation in a growth chamber or field can also damage plants, decreasing the growth and productivity of economically important crops, including rice; UV radiation exclusion prevents such damage and can increase plant growth 2,3 .Rice is one of the most important staple grains globally and is extensively cultivated worldwide in regions with different climates. The genus Oryza comprises 22 wild species and 2 species of cultivated rice (Oryza sativa L. and O. glaberrima Steud.); O. sativa and O. glaberrima originated from and were domesticated in Asia and West Africa, respectively 4,5 . Asian rice cultivars belong to one of the two major O. sativa subspecies, japonica or indica. UVB sensitivity varies widely among Asian rice cultivars 6 due to differences in the enzymatic activity for repair of UV-induced DNA damage 7 . Upon UVB irradiation, cyclobutane pyrimidine dimers (CPDs) are formed between adjacent pyrimidines on the same DNA strand 8 . In the photoreactivation pathway, the enzyme photolyase absorbs light in the UVA (315-400 nm) and blue ranges through the FAD chromophore, which releases energy to induce dimer dissociation into monomers 9 . Photoreactivation activity is higher in the UVB-resistant rice cultivar Sasanishiki (O. sativa ssp. japonica) than in the less resistant cultivar Norin 1 (also japonica) 10 . The higher activity in Sasanishiki results from spontaneous mutations in the CPD photolyase gene that alter the function of the enzyme rather than from a regulatory mutation 11 . The ...

Background: More than 1 year after the beginning of the international spread of coronavirus 2019 (COVID-19), the reasons explaining its apparently lower reported burden in Africa are still to be fully elucidated. Few studies previously investigated the potential reasons explaining this epidemiological observation using data at the level of a few African countries. However, an updated analysis considering the various epidemiological waves and variables across an array of categories, with a focus on African countries might help to better understand the COVID-19 pandemic on the continent. Thus, we investigated the potential reasons for the persistently lower transmission and mortality rates of COVID-19 in Africa.Methods: Data were collected from publicly available and well-known online sources. The cumulative numbers of COVID-19 cases and deaths per 1 million population reported by the African countries up to February 2021 were used to estimate the transmission and mortality rates of COVID-19, respectively. The covariates were collected across several data sources: clinical/diseases data, health system performance, demographic parameters, economic indicators, climatic, pollution, and radiation variables, and use of social media. The collinearities were corrected using variance inflation factor (VIF) and selected variables were fitted to a multiple regression model using the R statistical package.Results: Our model (adjusted R-squared: 0.7) found that the number of COVID-19 tests per 1 million population, GINI index, global health security (GHS) index, and mean body mass index (BMI) were significantly associated (P < 0.05) with COVID-19 cases per 1 million population. No association was found between the median life expectancy, the proportion of the rural population, and Bacillus Calmette–Guérin (BCG) coverage rate. On the other hand, diabetes prevalence, number of nurses, and GHS index were found to be significantly associated with COVID-19 deaths per 1 million population (adjusted R-squared of 0.5). Moreover, the median life expectancy and lower respiratory infections rate showed a trend towards significance. No association was found with the BCG coverage or communicable disease burden.Conclusions: Low health system capacity, together with some clinical and socio-economic factors were the predictors of the reported burden of COVID-19 in Africa. Our results emphasize the need for Africa to strengthen its overall health system capacity to efficiently detect and respond to public health crises.

Background The COVID-19 respiratory illness caused by the SARS-CoV-2 has been a major cause of morbidity and mortality worldwide since the first reported case in Wuhan, China. A year has passed since pandemic began, and the reasons for different COVID-19 burden variation across continents keep puzzling the general public. Main body of the abstract Since the COVID-19 pandemic started, published research articles have addressed the epidemiological risk factors, host factors, susceptibility and immunity. To ascertain possible reasons for the different rates of COVID-19 infections between Africa and other continents, we summarized the up-to-date scientific literature to identify possible arguments in this regard. Available literature suggests that demographic, epidemiological, sociological, genetic and immunological factors contribute in the COVID-19 severity and the susceptibly to SARS-CoV-2. Short conclusion This review summarizes existing data and discusses reasons for differential COVID-19 burden across continents. The arguments mentioned herein will be helpful to guide future experimental studies to test different hypotheses.

Sensitivity to ultraviolet-B (UVB, 280–315 nm) radiation varies widely among rice (Oryza sativa) cultivars due to differences in the activity of cyclobutane pyrimidines dimer (CPD) photolyase. Interestingly, cultivars with high UVB sensitivity and low CPD photolyase activity have been domesticated in tropical areas with high UVB radiation. Here, we investigated how differences in CPD photolyase activity affect plant resistance to the rice blast fungus, Magnaporthe oryzae, which is one of the other major stresses. We used Asian and African rice cultivars and transgenic lines with different CPD photolyase activities to evaluate the interaction effects of CPD photolyase activity on resistance to M. oryzae. In UVB-resistant rice plants overexpressing CPD photolyase, 12 h of low-dose UVB (0.4 W m−2) pretreatment enhanced sensitivity to M. oryzae. In contrast, UVB-sensitive rice (transgenic rice with antisense CPD photolyase, A-S; and rice cultivars with low CPD photolyase activity) showed resistance to M. oryzae. Several defense-related genes were upregulated in UVB-sensitive rice compared to UVB-resistant rice. UVB-pretreated A-S plants showed decreased multicellular infection and robust accumulation of reactive oxygen species. High UVB-induced CPD accumulation promoted defense responses and cross-protection mechanisms against rice blast disease. This may indicate a trade-off between high UVB sensitivity and biotic stress tolerance in tropical rice cultivars. Graphical Abstract