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Aquaporins (AQPs) are channel-forming integral membrane proteins that transport water and other small solutes across biological membranes. Despite the vital role of AQPs, to date, little is known in physic nut (Jatropha curcas L., Euphorbiaceae), an important non-edible oilseed crop with great potential for the production of biodiesel. In this study, 32 AQP genes were identified from the physic nut genome and the family number is relatively small in comparison to 51 in another Euphorbiaceae plant, rubber tree (Hevea brasiliensis Muell. Arg.). Based on the phylogenetic analysis, the JcAQPs were assigned to five subfamilies, i.e., nine plasma membrane intrinsic proteins (PIPs), nine tonoplast intrinsic proteins (TIPs), eight NOD26-like intrinsic proteins (NIPs), two X intrinsic proteins (XIPs), and four small basic intrinsic proteins (SIPs). Like rubber tree and other plant species, functional prediction based on the aromatic/arginine selectivity filter, Froger's positions, and specificity-determining positions showed a remarkable difference in substrate specificity among subfamilies of JcAQPs. Genome-wide comparative analysis revealed the specific expansion of PIP and TIP subfamilies in rubber tree and the specific gene loss of the XIP subfamily in physic nut. Furthermore, by analyzing deep transcriptome sequencing data, the expression evolution especially the expression divergence of duplicated HbAQP genes was also investigated and discussed. Results obtained from this study not only provide valuable information for future functional analysis and utilization of Jc/HbAQP genes, but also provide a useful reference to survey the gene family expansion and evolution in Euphorbiaceae plants and other plant species.

Hydrogels of numerous chemical compositions have achieved high fracture toughness on the basis of one physical principle. As a crack advances in such a hydrogel, a polymer network of strong bonds ruptures at the front of the crack and elicits energy dissipation in the bulk of the hydrogel. The constituent that dissipates energy in the bulk of the hydrogel is called a toughener. A hypothesis has emerged recently that tougheners increase fracture toughness greatly but contribute little to fatigue threshold. Here we ascertain this hypothesis by studying hydrogels of two kinds, identical in all aspects except for tougheners. A Ca-alginate/polyacrylamide hydrogel has ionic bonds, which act as tougheners, resulting in a toughness of 3375 J/m2 and a threshold of 35 J/m2. A Na-alginate/polyacrylamide hydrogel has no ionic bonds, resulting in a toughness of 169 J/m2 and a threshold of 17 J/m2. These results motivate a discussion on the development of fatigue-resistant hydrogels.

BackgroundNatural rubber, an important industrial raw material, is specifically synthesized in laticifers located inside the rubber tree (Hevea brasiliensis Muell. Arg.) trunk. Due to the absence of plasmodesmata, the laticifer water balance is mediated by aquaporins (AQPs). However, to date, the characterization of H. brasiliensis AQPs (HbAQPs) is still in its infancy.ResultsIn this study, 51 full-length AQP genes were identified from the rubber tree genome. The phylogenetic analysis assigned these AQPs to five subfamilies, including 15 plasma membrane intrinsic proteins (PIPs), 17 tonoplast intrinsic proteins (TIPs), 9 NOD26-like intrinsic proteins (NIPs), 4 small basic intrinsic proteins (SIPs) and 6 X intrinsic proteins (XIPs). Functional prediction based on the analysis of the aromatic/arginine (ar/R) selectivity filter, Froger’s positions and specificity-determining positions (SDPs) showed a remarkable difference in substrate specificity among subfamilies. Homology analysis supported the expression of 44 HbAQP genes in at least one of the examined tissues. Furthermore, deep sequencing of the laticifer transcriptome in the form of latex revealed a key role of several PIP subfamily members in the laticifer water balance, and qRT-PCR analysis showed diverse expression patterns of laticifer-expressed HbAQP genes upon ethephon treatment, a widely-used practice for the stimulation of latex yield.ConclusionsThis study provides an important genetic resource of HbAQP genes, which will be useful to improve the water use efficiency and latex yield of Hevea.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2152-6) contains supplementary material, which is available to authorized users.