Functional characterization of a bark-specific monoterpene synthase potentially involved in wounding- and methyl jasmonate-induced linalool emission in rubber (Hevea brasiliensis).

Rubber (Hevea brasiliensis) is a latex-producing plant that often encounters mechanical wounding, as well as pathogen and pest attacks through wound sites during and after tapping. Terpenoids play an important role in the ecological interactions of many plant species, and their diversity is mainly generated by enzymes known as terpene synthases (TPS). In this study, one cDNA sequence encoding a putative terpene synthase, HbTPS20, was obtained from the bark tissues of H. brasiliensis. The encoded protein contains 610 amino acids with a putative N-terminal plastid transit peptide of approximately 70 residues. It belongs to the TPS-b subfamily. Further phylogenetic analysis showed that HbTPS20 formed a separate branch that diverged from the progenitor of all other potentially functional terpene synthases of the rubber TPS-b subfamily. The truncated HbTPS20 without the signal peptide coding sequence was successfully expressed in E. coli and in vitro enzymatic assays with geranyl diphosphate (GPP) or neryl diphosphate (NPP) as a substrate defined HbTPS20 as an active linalool synthase (HbLIS) with the ability to produce linalool as the principal product. RT-qPCR analysis showed that the highest transcript levels of HbTPS20 were found in barks, and this gene was expressed at 2.26- and 250-fold greater levels in the bark tissues of wounded and MeJA-treated plants, respectively, than in those of the control plants. This indicates that this gene may be involved in the induced stress responses of rubber.

The Antimalarial Chloroquine Reduces the Burden of Persistent Atrial Fibrillation.

In clinical practice, reducing the burden of persistent atrial fibrillation by pharmacological means is challenging. We explored if blocking the background and the acetylcholine-activated inward rectifier potassium currents (IK1 and IKACh) could be antiarrhythmic in persistent atrial fibrillation. We thus tested the hypothesis that blocking IK1 and IKACh with chloroquine decreases the burden of persistent atrial fibrillation. We used patch clamp to determine the IC50 of IK1 and IKACh block by chloroquine and molecular modeling to simulate the interaction between chloroquine and Kir2.1 and Kir3.1, the molecular correlates of IK1 and IKACh. We then tested, as a proof of concept, if oral chloroquine administration to a patient with persistent atrial fibrillation can decrease the arrhythmia burden. We also simulated the effects of chloroquine in a 3D model of human atria with persistent atrial fibrillation. In patch clamp the IC50 of IK1 block by chloroquine was similar to that of IKACh. A 14-day regimen of oral chloroquine significantly decreased the burden of persistent atrial fibrillation in a patient. Mathematical simulations of persistent atrial fibrillation in a 3D model of human atria suggested that chloroquine prolonged the action potential duration, leading to failure of reentrant excitation, and the subsequent termination of the arrhythmia. The combined block of IK1 and IKACh can be a targeted therapeutic strategy for persistent atrial fibrillation.