Analysis of the inhibition potential of zosuquidar derivatives on selected bacterial and fungal ABC transporters

Abstract

The increasing number of multidrug-resistant pathogenic microorganisms is a serious public health issue. Among the multitude of mechanisms that lead to multidrug resistance, the active extrusion of toxic compounds, mediated by MDR efflux pumps, plays an important role. In our study we analyzed the inhibitory capability of 26 synthesized zosuquidar derivatives on three ABC-type MDR efflux pumps, namely Saccharomyces cerevisiae Pdr5 as well as Lactococcus lactis LmrA and LmrCD. For Pdr5, five compounds could be identified that inhibited rhodamine 6G transport more efficiently than zosuquidar. One of these is a compound with a new catechol acetal structure that might represent a new lead compound. Furthermore, the determination of IC₅₀ values for rhodamine 6G transport of Pdr5 with representative compounds reveals values between 0.3 and 0.9 μM. Thus the identified compounds are among the most potent inhibitors known for Pdr5. For the ABC-type efflux pumps LmrA and LmrCD from L. lactis, seven and three compounds, which inhibit the transport activity more than the lead compound zosuquidar, were found. Interestingly, transport inhibition for LmrCD was very specific, with a drastic reduction by one compound while its diastereomers showed hardly an effect. Thus, the present study reveals new potent inhibitors for the ABC-type MDR efflux pumps studied with the inhibitors of Pdr5 and LmrCD being of particular interest as these proteins are well known model systems for their homologs in pathogenic fungi and Gram-positive bacteria.     

A morphometric study of the midgut in resistant and non-resistant Anticarsia gemmatalis (Hübner) (Lepidoptera: Noctuidae) larvae to its nucleopolyhedrovirus (AgMNPV)

In this investigation, the anterior and posterior regions of the midgut of resistant (RL) and non-resistant (SL) Anticarsia gemmatalis larvae were analyzed morphometrically to characterize different regions along their length. Also, this investigation compares the results between SL and RL to improve the understanding of the resistance mechanisms to the virus. Histological sections were analyzed in a computerized system and the data were statistically analyzed by the Kruskal-Wallis test and by multivariate analysis. The midguts are morphometrically different in the two larval populations; we observed higher values in RL. The morphometric analysis of the epithelial cells showed that only columnar and goblet cells were distinct along the midgut, in both larvae, with the higher values found in the anterior region. Comparing the results between the two larval populations, all the epithelial cells presented significant differences, with RL showing the higher morphometric values. We concluded that there are regional differences along the length of midgut in SL and RL that confirm the idea of two morpho-functional distinct regions. The consistently morphometric superior values in RL indicate that this variability can be related with the resistance of A. gemmatalis to its AgMNPV.     

Preferential expression of a plant cystatin at nematode feeding sites confers resistance to Meloidogyne incognita and Globodera pallida

The expression patterns of three promoters preferentially active in the roots of Arabidopsis thaliana have been investigated in transgenic potato plants in response to plant parasitic nematode infection. Promoter regions from the three genes, TUB-1, ARSK1 and RPL16A were linked to the GUS reporter gene and histochemical staining was used to localize expression in potato roots in response to infection with both the potato cyst nematode, Globodera pallida and the root-knot nematode, Meloidogyne incognita. All three promoters directed GUS expression chiefly in root tissue and were strongly up-regulated in the galls induced by feeding M. incognita. Less activity was associated with the syncytial feeding cells of the cyst nematode, although the ARSK1 promoter was highly active in the syncytia of G. pallida infecting soil grown plants. Transgenic potato lines that expressed the cystatin OcIDeltaD86 under the control of the three promoters were evaluated for resistance against Globodera sp. in a field trial and against M. incognita in containment. Resistance to Globodera of 70 +/- 4% was achieved with the best line using the ARSK1 promoter with no associated yield penalty. The highest level of partial resistance achieved against M. incognita was 67 +/- 9% using the TUB-1 promoter. In both cases this was comparable to the level of resistance achieved using the constitutive cauliflower mosaic virus 35S (CaMV35S) promoter. The results establish the potential for limiting transgene expression in crop plants whilst maintaining efficacy of the nematode defence.     

Virus adaptation to quantitative plant resistance: erosion or breakdown?

Adaptation of populations to new environments is frequently costly due to trade‐offs between life history traits, and consequently, parasites are expected to be locally adapted to sympatric hosts. Also, during adaptation to the host, an increase in parasite fitness could have direct consequences on its aggressiveness (i.e. the quantity of damages caused to the host by the virus). These two phenomena have been observed in the context of pathogen adaptation to host's qualitative and monogenic resistances. However, the ability of pathogens to adapt to quantitative polygenic plant resistances and the consequences of these potential adaptations on other pathogen life history traits remain to be evaluated. Potato virus Y and two pepper genotypes (one susceptible and one with quantitative resistance) were used, and experimental evolutions showed that adaptation to a quantitative resistance was possible and resulted in resistance breakdown. This adaptation was associated to a fitness cost on the susceptible cultivar, but had no consequence either in terms of aggressiveness, which could be explained by a high tolerance level, or in terms of aphid transmission efficiency. We concluded that quantitative resistances are not necessarily durable but management strategies mixing susceptible and resistant cultivars in space and/or in time should be useful to preserve their efficiency.     

抗大麦黄矮病的小偃麦易位系的创制与鉴定

抗大麦黄矮病的小偃麦易位系的创制与鉴定@辛志勇$中国农业科学院作物育种载培研究所!北京100081@张增燕$中国农业科学院作物育种载培研究所!北京100081@陈孝$中国农业科学院作物育种载培研究所!北京100081@林志珊$中国农业科学院作物育种载培研究所!北京100081大麦;;小偃麦;;易位系     

Experimentally increased group diversity improves disease resistance in an ant species

A leading hypothesis linking parasites to social evolution is that more genetically diverse social groups better resist parasites . Moreover, group diversity can encompass factors other than genetic variation that may also influence disease resistance. Here, we tested whether group diversity improved disease resistance in an ant species with natural variation in colony queen number. We formed experimental groups of workers and challenged them with the fungal parasite Metarhizium anisopliae . Workers originating from monogynous colonies (headed by a single queen and with low genetic diversity) had higher survival than workers originating from polygynous ones, both in uninfected groups and in groups challenged with M. anisopliae . However, an experimental increase of group diversity by mixing workers originating from monogynous colonies strongly increased the survival of workers challenged with M. anisopliae , whereas it tended to decrease their survival in absence of infection. This experiment suggests that group diversity, be it genetic or environmental, improves the mean resistance of group members to the fungal infection, probably through the sharing of physiological or behavioural defences.     

Natural convection from leaves at realistic Grashof numbers

Abstract. The boundary layer resistance of model leaves was measured in still air, at a range of leaf-to-air temperature differences. The results were compared to those calculated from standard formulae for natural convection. The agreement between observed and calculated was only satisfactory when Grashof numbers exceeded about 105. At the lower Grashof numbers, which often prevail in nature, the observed rates of heat transfer considerably exceeded those calculated.     

Stimulation and attenuation of induced resistance by elicitors and inhibitors of chemical induction in tomato (Lycopersicon esculentum) foliage

Elicitors and inhibitors of chemical induction were used to manipulate the activities of several putative defense-related proteins in leaves of the tomato, Lycopersicon esculentum Mill. The four presumptive defenses manipulated were proteinase inhibitors, polyphenol oxidase, peroxidase, and lipoxygenase. The elicitors used were jasmonic acid, methyl jasmonate, ultraviolet light, and feeding by larvae of the noctuid, Helicoverpa zea Boddie; the inhibitors used were salicylic acid and acetylsalicylic acid. These chemical manipulations were combined with short-term growth assays using larvae of the generalist noctuid, Spodoptera exigua Hubner, in order to assess the relative roles of the proteins in induced resistance to S. exigua. When activities of proteinase inhibitors and/or polyphenol oxidase in leaf tissue were high (e.g., in damaged or elicited plants), growth rates of larvae of S. exigua were low; when activities of polyphenol oxidase and proteinase inhibitors were low (e.g., in undamaged or damaged, inhibited plants), growth rates of larvae were high. In contrast, high activities of peroxidase and lipoxygenase were not associated with decreases in suitability of leaf tissue for S. exigua. The association of high levels of proteinase inhibitors and polyphenol oxidase with resistance to S. exigua – irrespective of the presence or absence of damage – strongly implicates these proteins as causal agents in induced resistance to S. exigua.