Aminoacylation of Plasmodium falciparum tRNAAsn and Insights in the Synthesis of Asparagine Repeats

Genome sequencing revealed an extreme AT-rich genome and a profusion of asparagine repeats associated with low complexity regions (LCRs) in proteins of the malarial parasite Plasmodium falciparum. Despite their abundance, the function of these LCRs remains unclear. Because they occur in almost all families of plasmodial proteins, the occurrence of LCRs cannot be associated with any specific metabolic pathway; yet their accumulation must have given selective advantages to the parasite. Translation of these asparagine-rich LCRs demands extraordinarily high amounts of asparaginylated tRNA^Asn. However, unlike other organisms, Plasmodium codon bias is not correlated to tRNA gene copy number. Here, we studied tRNA^Asn accumulation as well as the catalytic capacities of the asparaginyl-tRNA synthetase of the parasite in vitro. We observed that asparaginylation in this parasite can be considered standard, which is expected to limit the availability of asparaginylated tRNA^Asn in the cell and, in turn, slow down the ribosomal translation rate when decoding asparagine repeats. This observation strengthens our earlier hypothesis considering that asparagine rich sequences act as “tRNA sponges” and help cotranslational folding of parasite proteins. However, it also raises many questions about the mechanistic aspects of the synthesis of asparagine repeats and about their implications in the global control of protein expression throughout Plasmodium life cycle.     

Comparative Study of the Interactive Effects of Salinity and Phosphorus Availability in Wild (Hordeum maritimum) and Cultivated Barley (H. vulgare)

The present study aimed to compare the effects of phosphorus (P) deficiency applied only or combined with salinity on root response, P partitioning, acid phosphatase activity, and phenolic compounds in wild (Hordeum maritimum) and cultivated (H. vulgare) barley species. Seedlings were grown hydroponically under low or sufficient P supply, with or without 100 mM NaCl for 55 days. Results showed that, when individually applied, P deficiency and salinity restricted the whole plant relative growth rate in both species of barley, with a more pronounced impact of the former stress. These depressive effects were more pronounced in H. vulgare than in H. maritimum. The combined effects of P deficiency and salinity were not additive neither on whole plant RGR nor on root response parameters in both species. The root area, root/shoot P content, root and leaf acid phosphatase activities, and shoot flavonoids contents increased under P deficiency conditions with and without salt in both species. Overall, the relatively better tolerance of H. maritimum plants to P deficiency applied only or combined with salinity could be explained by the capacity of this species to maintain higher P acquisition efficiency in concomitance with a larger root system, a higher root/shoot DW ratio, a higher root/shoot P content, a greater root and leaf acid phosphatase activities, and a higher flavonoid content and antioxidant capacity under combined effects of both stresses. Thus, H. maritimum constitutes a promising model to ameliorate the tolerance of the cultivated barley species under low-P soils and/or saline regions.     

Electrophoretic detection of protein fractions in extracts of the ocular tentacles of Helix aspersa Müller, 1774 (Gasteropoda, Pulmonata, Helicidae)

The extracts from ocular tentacles of Helix aspersa hare a heterochronic inhibitive action on the development of albumen gland. In view of elucidating the origin of this heterochrony, we make an electrophoretic study of the different extracts from juveniles, adults in activity, in natural sleep and awakning. This study has allowed us to spot 19 proteic fractions common to the four extracts of the tentacles under study, but these fractions show only differences in concentration. Particularly, the proteinic fractions 7 and 8 are more concentrated in the extract of juveniles snails tentacles than in the extract of adults snails. This difference in proteic concentration could explain the heterochronic inhibitive action of ocular tentacles extracts on the development of albumen gland of this snail.     

Climate change-induced ecosystem disturbance: a review on sclerophyllous and semi-deciduous forests in Tunisia

According to the sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC), global climate change is now unequivocal. Tunisia, like many other countries, has been affected by climate changes, including rising temperatures, intense heatwaves, and altered precipitation regimes. Tunisia's mean annual temperatures has risen about +1.4 °C in the twentieth century, with the most rapid warming taking place since the 1970s. Drought represents a primary contributing factor to tree decline and dieback. Long-term drought can result in reduced growth and health of trees, thereby increasing their susceptibility to insect pests and pathogens. Reported increases in tree mortality point toward accelerating global forest vulnerability under hotter temperatures and longer, more intense droughts. In order to assess the effect of these climate changes on the current state of forest ecosystems in Tunisia and their evolution, an investigative study was required. Here, we review the current state of knowledge on the effects of climate change on sclerophyllous and semi-deciduous forest ecosystems in Tunisia. Natural disturbance during recent years, as well as the adaptability and resilience of some forest species to climate change, were surveyed. The Standardized Precipitation Evapotranspiration Index (SPEI) is a multi-scalar drought index based on climate data that has been used to analyse drought variability. The SPEI time scale analysis showed a negative trend over the 1955–2021 period in Tunisian forest regions. In 2021, Tunisia lost 280 km² of tree cover to fires, which is equivalent to 26% of the total lost area between 2008 and 2021. Changing climate conditions have also affected phenological parameters, with an advance in the start of the green season (SOS) of 9.4 days, a delay at the end of the green season (EOS) of 5 days, with a consequent extended duration of the green season (LOS) by an average of 14.2 days. All of these alarming findings invite us to seek adaptation strategies for forest ecosystems. Adapting forests to climate change is therefore a challenge for scientists as well as policymakers and managers.