Getting the most sulfate from soil: Regulation of sulfate uptake transporters in Arabidopsis.

Sulfur (S) is an essential macronutrient for all living organisms. Plants require large amounts of sulfate for growth and development, and this serves as a major entry point of sulfate into the food web. Plants acquire S in its ionic form from the soil; they have evolved tightly controlled mechanisms for the regulation of sulfate uptake in response to its external and internal availability. In the model plant Arabidopsis thaliana, the first key step in sulfate uptake is presumed to be carried out exclusively by only two high-affinity sulfate transporters: SULTR1;1 and SULTR1;2. A better understanding of the mode of regulation for these two transporters is crucial because they constitute the first determinative step in balancing sulfate in respect to its supply and demand. Here, we review the recent progress achieved in our comprehension of (i) mechanisms that regulate these two high-affinity sulfate transporters at the transcriptional and post-transcriptional levels, and (ii) their structure-function relationship. Such progress is important to enable biotechnological and agronomic strategies aimed at enhancing sulfate uptake and improving crop yield in S-deficient soils.

Covariation between colony social structure and immune defences of workers in the ant Formica selysi

Several ant species vary in the number of queens per colony, yet the causes and consequences of this variation remain poorly understood. In previous experiments, we found that Formica selysi workers originating from multiple-queen (=polygyne) colonies had a lower resistance to a fungal pathogen than workers originating from single-queen (=monogyne) colonies. In contrast, group diversity improved disease resistance in experimental colonies. This discrepancy between field and experimental colonies suggested that variation in social structure in the field had antagonistic effects on worker resistance, possibly through a down-regulation of the immune system balancing the positive effect of genetic diversity. Here, we examined if workers originating from field colonies with alternative social structure differed in three major components of their immune system. We found that workers from polygyne colonies had a lower bacterial growth inhibitory activity than workers from monogyne colonies. In contrast, workers from the two types of colonies did not differ significantly in bacterial cell wall lytic activity and prophenoloxidase activity. Overall, the presence of multiple queens in a colony correlated with a slight reduction in one inducible component of the immune system of individual workers. This reduced level of immune defence might explain the lower resistance of workers originating from polygyne colonies despite the positive effect of genetic diversity. More generally, these results indicate that social changes at the group level can modulate individual immune defences.