Five TPSs are responsible for volatile terpenoid biosynthesis in Albizia julibrissin.

Silk tree, Albizia julibrissin Duraz, is an old ornamental plant and extensively cultivated in Asia. Previous works have discovered that the terpenoids were the dominating compounds in the floral VOC of A. julibrissin, however the biosynthesis of these terpenoids was poorly understood so far. Here, 11 terpene synthase genes (TPSs) were identified by transcriptome sequencing that fell into TPS-a, TPS-b and TPS-g subfamilies. The enzymatic activity tests showed that five genes were functional: AjTPS2 was a sesquiterpene synthase and produced α-farnesene and (Z, E)-ß-farnesene; AjTPS5 was able to catalyze the formation of five monoterpenes and nine sesquiterpenes; AjTPS7, AjTPS9 and AjTPS10 were dedicated monoterpene synthases, as AjTPS7 and AjTPS10 formed the single product ß-ocimene and linalool, respectively, and AjTPS9 produced γ-terpinene with other three monoterpenes. More importantly, the main catalytic products of the characterized AjTPSs were consistent with the terpenoids observed in A. julibrissin volatiles. Combining terpene chemistry, TPSs biochemical activities and gene expression analysis, we demonstrate that AjTPS2, AjTPS5, AjTPS7, AjTPS9 and AjTPS10 are responsible for the volatile terpenoids biosynthesis in A. julibrissin.

Graphene quantum dots as cysteine protease nanocarriers against stored grain insect pests.

Storing grains remain vulnerable to insect pest attack. The present study developed a biopesticide using biomolecules and their encapsulation in nanoparticles. A 25 kDa cysteine protease extracted from seeds of Albizia procera (ApCP) was encapsulated in graphene quantum dots (GQDs). The insecticidal activity of ApCP, with or without GQDs, against two stored grain insect pests, Tribolium castaneum (Herbst) and Rhyzopertha dominica (Fabricius) was explored. Insects were exposed to three concentrations 7.0, 3.5 and 1.7 mg of ApCP per a gram of wheat flour and grains. The insecticidal activity of ApCP encapsulated with GQDs was improved compared to that of ApCP without GQDs for both insect pests. The number of eggs and larvae of T. castaneum was reduced by 49% and 86%, respectively. Larval mortality was increased to 72%, and adult eclosion of T. castaneum was reduced by 98% at a 7.0 mg/g concentration of ApCP with GQDs compared to that of ApCP without GQDs. Exposure to 7.0 mg/g ApCP with GQDs, the number of R. dominica eggs and larvae was reduced by 72% and 92% respectively, larval mortality was increased by 90%, and eclosion was reduced by 97%. The extraction, purification, characterization, quantification and encapsulation of ApCP with GQDs were also studied. Cysteine protease nanocarriers have the potential to control stored grain insect pests.