Do foliar endophytes affect grass litter decomposition? A microcosm approach using Lolium multiflorum

Symbiotic infection with fungal endophytes has been shown to decrease herbivory in several temperate grasses. We tested the hypothesis that foliar endophytes of grasses may also affect below-ground processes upon their host death, by altering the litter quality for detritivores or the microenvironment for decomposition. Microcosm–litterbag experiments were used to assess decay rates for litter produced by endophyte ( Neotyphodium sp.) infected vs uninfected Lolium multiflorum plants, and to examine endophyte-mediated effects of prior site occupants on current litter decomposition. We found that litter from endophyte-infected L. multiflorum decomposed more slowly than litter from endophyte-free conspecifics and from a naturally uninfected grass, Bromus unioloides . Furthermore, the endophyte–grass association modified the decomposition environment, so that B. unioloides litter decomposed faster when placed underneath a thick layer of endophyte-free L. multiflorum litter. Litter decay rates increased with the amount of root debris remaining in situ from the previous season, but were not affected by the infection status of prior site occupants. The lower decomposability of litter from infected L. multiflorum plants persisted across a range of microenvironments, as determined by different amounts of above-ground litter and soil moisture conditions. Endophyte infection tended to reduce the N content of decaying litter; however, litter N and C/N ratio mainly accounted for interspecific differences in decomposition. Our results imply that fungal endophytes not only can affect herbivory food chains, but also soil organisms and the ecosystem processes they regulate. This study suggests a novel role for symbiotic foliar endophytes in linking above-ground and below-ground sub-systems.     

Glutathionylation of the p50 subunit of NF-kappaB: a mechanism for redox-induced inhibition of DNA binding.

The cellular redox status can modify the function of NF-kappaB, whose DNA-binding activity can be inhibited by oxidative, nitrosative, and nonphysiological agents such as diamide, iodoacetamide, or N-ethylmaleimide. This inhibitory effect has been proposed to be mediated by the oxidation of a conserved cysteine in its DNA-binding domain (Cys62) through unknown biochemical mechanisms. The aim of this work was to identify new oxidative modifications in Cys62 involved in the redox regulation of the NF-kappaB subunit p50. To address this problem, we exposed p50, both the native form (p50WT) and its corresponding mutant in Cys62 (C62S), to changes in the redox pair glutathione/glutathione disulfide (GSH/GSSG) ratio ranging from 100 to 0.1, which may correspond to intracellular (patho)physiological states. A ratio between 1 and 0.1 resulted in a 40-70% inhibition of the DNA binding of p50WT, having no effect on the C62S mutant. Mass spectrometry studies, molecular modeling, and incorporation of (3)H-glutathione assays were consistent with an S-glutathionylation of p50WT in Cys62. Maximal incorporation of (3)H-glutathione to the p50WT and C62S was of 0.4 and 0.1 mol of (3)H-GSH/mol of protein, respectively. Because this covalent glutathione incorporation did not show a perfect correlation with the observed inhibition in the DNA-binding activity of p50WT, we searched for other modifications contributing to the maximal inhibition. MALDI-TOF and nanospray-QIT studies revealed the formation of sulfenic acid as an alternative or concomitant oxidative modification of p50. In summary, these data are consistent with new oxidative modifications in p50 that could be involved in redox regulatory mechanisms for NF-kappaB. These postranslational modifications could represent a molecular basis for the coupling of pro-oxidative stimuli to gene expression.     

Isolated Potato Virus A coat protein possesses unusual properties and forms different short virus-like particles

In our previous study, we have observed that the isolated coat proteins (CP) of the Potyvirus Potato Virus A (PVA) virions exhibit an intrinsic tendency to self-associate into various multimeric forms containing some fractions of cross-β-structure. In this report, we studied the effect of solution conditions on the structure and dissociation of isolated PVA CP using a number of complementary physicochemical methods. Analysis of the structure of PVA CP in solution was performed by limited proteolysis with MALDI-TOF mass spectrometry analysis, transmission electron microscopy, intrinsic fluorescence spectroscopy, and synchrotron small angle X-ray scattering (SAXS). Overall structural characteristics of PVA CP obtained by combination of these methods and ab initio shape reconstruction by SAXS show that PVA CP forms large multi-subunit particles. We demonstrate that a mixture of compact virus-like particles (VLP) longer than 30 nm is assembled on dialysis of isolated CP into neutral pH buffer (at low ionic strength). Under conditions of high ionic strength (0.5 M NaCl) and high pH (pH 10.5), PVA dissociates into low compactness oval-shaped particles of approximately 30 subunits (20–30 nm). The results of limited trypsinolysis of these particles (enzyme/substrate ratio 1:100, 30 min) showed the existence of non-cleavable core-fragment, consisting of 137 amino acid residues. Trypsin treatment removed only a short N-terminal fragment in the intact virions. These particles are readily reassembled into regular VLPs by changing pH back to neutral. It is possible that these particles may represent some kind of intermediate in PVA assembly in vitro and in vivo.     

Natural Killer Cells Control Tumor Growth by Sensing a Growth Factor

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