Ether Bond Cleavage of a Phenylcoumaran ß-5 Lignin Model Compound and Polymeric Lignin Catalysed by a LigE-type Etherase from Agrobacterium sp.

A LigE-type beta-etherase enzyme from lignin-degrading Agrobacterium sp. has been identified, which assists degradation of polymeric lignins. Testing against lignin dimer model compounds revealed that it does not catalyse the previously reported reaction of Sphingobium SYK-6 LigE, but instead shows activity for a ß-5 phenylcoumaran lignin dimer. The reaction products did not contain glutathione, indicating a catalytic role for reduced glutathione in this enzyme. Three reaction products were identified: the major product was a cis-stilbene arising from C-C fragmentation involving loss of formaldehyde; two minor products were an alkene arising from elimination of glutathione, and an oxidised ketone, proposed to arise from reaction of an intermediate with molecular oxygen. Testing of the recombinant enzyme against a soda lignin revealed the formation of new signals by two-dimensional NMR analysis, whose chemical shifts are consistent with the formation of a stilbene unit in polymeric lignin.

Vitislactone, a non-canonical strigolactone exudated by grapevine rootstocks in response to nitrogen starvation.

Strigolactones are compounds produced by plant roots in response to nutrient deficiency, acting both as local and systemic signals to control development and nutrition. Strigolactones are exuded in the rhizosphere to positively influence interactions with beneficial microbes. LC-MS/MS analysis shows that two genetically distinct grapevine rootstocks exudate one or two non-canonical strigolactones when subjected to low nitrogen conditions. Gene expression profiles and orobanche seed germination assays confirm that the biosynthesis and exudation of non-canonical compounds is the preferred pathway. The first compound, corresponding to heliolactone or 6-epi-heliolactone, is only exuded by the rootstock showing lower shoot branching and a higher level of mycorrhization with arbuscular mycorrhizal fungi. The structure of the second compound exuded by both rootstocks was identified by NMR and LC-MS/MS analysis. It is a non-canonical strigolactone, which has never been identified in another species. This first identification of a natural compound with the potential to stimulate beneficial root-microbe interactions in grapevines opens new perspectives in viticulture.

Synthesis, Physical Properties and Application of a Series of New Polyoxometalate-Based Ionic Liquids.

This paper deals with the preparation and the characterization of four new ionic liquids resulting from the pairing of various polyoxotungstates or polyoxomolybdates with the cation trihexyltetradecylphosphonium. The physical properties measured by different techniques evidence that the viscosity and the rheological behaviors of such POM-based ionic liquids, POM-ILs, strongly depend on the nature of the POM, especially its charge. Playing on the nature of the POM, we can indeed obtain Newtonian liquids or some much more viscous materials exhibiting characteristics of resins or pseudo-plastics. In a second part of this study, the potentialities of using such materials both as solvent and catalyst for the oxidation of a series of alcohols are presented as proof of concept. This part highlights great differences in strength and selectivity as a function of the POM-IL used. Furthermore, a very simple way to recycle the catalyst is also presented.

Increases in activity of proteasome and papain-like cysteine protease in Arabidopsis autophagy mutants: back-up compensatory effect or cell-death promoting effect?

Autophagy is essential for protein degradation, nutrient recycling, and nitrogen remobilization. Autophagy is induced during leaf ageing and in response to nitrogen starvation, and is known to play a fundamental role in nutrient recycling for remobilization and seed filling. Accordingly, ageing leaves of Arabidopsis autophagy mutants (atg) have been shown to over-accumulate proteins and peptides, possibly because of a reduced protein degradation capacity. Surprisingly, atg leaves also displayed higher protease activities. The work reported here aimed at identifying the nature of the proteases and protease activities that accumulated differentially (higher or lower) in the atg mutants. Protease identification was performed using shotgun LC-MS/MS proteome analyses and activity-based protein profiling (ABPP). The results showed that the chloroplast FTSH (FILAMENTATION TEMPERATURE SENSITIVE H) and DEG (DEGRADATION OF PERIPLASMIC PROTEINS) proteases and several extracellular serine proteases [subtilases (SBTs) and serine carboxypeptidase-like (SCPL) proteases] were less abundant in atg5 mutants. By contrast, proteasome-related proteins and cytosolic or vacuole cysteine proteases were more abundant in atg5 mutants. Rubisco degradation assays and ABPP showed that the activities of proteasome and papain-like cysteine protease were increased in atg5 mutants. Whether these proteases play a back-up role in nutrient recycling and remobilization in atg mutants or act to promote cell death is discussed in relation to their accumulation patterns in the atg5 mutant compared with the salicylic acid-depleted atg5/sid2 double-mutant, and in low nitrate compared with high nitrate conditions. Several of the proteins identified are indeed known as senescence- and stress-related proteases or as spontaneous cell-death triggering factors.