Modifications of membrane lipids in response to wounding of Arabidopsis thaliana leaves

Mechanical wounding of Arabidopsis thaliana leaves results in modifications of most membrane lipids within 6 hours. Here, we discuss the lipid changes, their underlying biochemistry, and possible relationships among activated pathways. New evidence is presented supporting the role of the processive galactosylating enzyme SENSITIVE TO FREEZING2 in the wounding response.     

No longer Demospongiae: Homoscleromorpha formal nomination as a fourth class of Porifera

Over the past few years, there has been growing interest among the sponge community in the phylogenetic position of the Homoscleromorpha (i.e. within or outside the class Demospongiae). Recent molecular analyses clearly show that the Homoscleromorpha forms a distinct clade separated from the Demospongiae and is composed of two families, Oscarellidae and Plakinidae. Within the currently more widely accepted hypothesis of a monophyletic Porifera, we formally propose here to raise Homoscleromorpha to the class rank (the fourth one). We, therefore, provide a definition and a formal diagnosis. In the supplementary materials, we also present an alternative classification of the Homoscleromorpha, following the PhyloCode.     

Positive role of reactive oxygen species in mammalian sperm capacitation: triggering and modulation of phosphorylation events

The role of reactive oxygen species (ROS) as signal transduction elements in physiological phenomena is a recent concept that changes the paradigm of these active species as harmful molecules that promote deleterious effects and even cell death. Capacitation is a term used to define a complex and not well-characterized process that allows spermatozoa to complete their preparation to fertilize oocytes. Spermatozoa from many species incubated under specific conditions have the ability to produce small amounts of ROS without harming cell function and rather promoting signal transduction pathways associated with capacitation. This review summarizes the findings regarding the role of ROS during mammalian sperm capacitation, specifically as physiological mediators that trigger phosphorylation events. The role of ROS as regulators of protein tyrosine phosphorylation has been known for a decade but other novel phosphorylations, such as those of PKA substrates, of MEK-like proteins, and of proteins with the threonine-glutamine-tyrosine motif, were recently evidenced. Here we stress the involvement of PKA and the ERK pathway as two signal mechanisms acting independently that contribute to the modulation of protein tyrosine phosphorylation required for spermatozoa to achieve capacitation. Moreover, integration of all these data reinforces the concept that although some phosphorylation events are independent of the others, cross talk is also needed among the various pathways involved.     

Secretion signal of the filamentous haemagglutinin, a model two-partner secretion substrate

The sorting of proteins to their proper subcellular compartment requires specific addressing signals that mediate interactions with ad hoc transport machineries. In Gram-negative bacteria, the widespread two-partner secretion (TPS) pathway is dedicated to the secretion of large, mostly virulence-related proteins. The secreted TpsA proteins carry a characteristic 250-residue-long N-terminal 'TPS domain' essential for secretion, while their TpsB transporters are pore-forming proteins that specifically recognize their respective TpsA partners and mediate their translocation across the outer membrane. However, the nature of the secretion signal has not been elucidated yet. The whooping cough agent Bordetella pertussis secretes its major adhesin filamentous haemagglutinin (FHA) via the TpsB transporter FhaC. In this work, we show specific interactions between an N-terminal fragment of FHA containing the TPS domain and FhaC by using two different techniques, an overlay assay and a pull-down of the complex. FhaC recognizes only non-native conformations of the TPS domain, corroborating the model that in vivo, periplasmic FHA is not yet folded. By generating single amino acid substitutions, we have identified interaction determinants forming the secretion signal. They are found unexpectedly far into the TPS domain and include both conserved and variable residues, which most likely explains the specificity of the TpsA-TpsB interaction. The N-terminal domain of FhaC is involved in the FHA-FhaC interaction, in agreement with its proposed function and periplasmic localization.