Saponins, a group of glycosidic compounds present in several plant species, have aglycone moieties that are formed using triterpenoid or steroidal skeletons. In spite of their importance as antimicrobial compounds and their possible benefits for human health, knowledge of the genetic control of saponin biosynthesis is still poorly understood. In the Medicago genus, the hemolytic activity of saponins is related to the nature of their aglycone moieties. We have identified a cytochrome P450 gene (CYP716A12) involved in saponin synthesis in Medicago truncatula using a combined genetic and biochemical approach. Genetic loss-of-function analysis and complementation studies showed that CYP716A12 is responsible for an early step in the saponin biosynthetic pathway. Mutants in CYP716A12 were unable to produce hemolytic saponins and only synthetized soyasaponins, and were thus named lacking hemolytic activity (lha). In vitro enzymatic activity assays indicate that CYP716A12 catalyzes the oxidation of β-amyrin and erythrodiol at the C-28 position, yielding oleanolic acid. Transcriptome changes in the lha mutant showed a modulation in the main steps of triterpenic saponin biosynthetic pathway: squalene cyclization, β-amyrin oxidation, and glycosylation. The analysis of CYP716A12 expression in planta is reported together with the sapogenin content in different tissues and stages. This article provides evidence for CYP716A12 being a key gene in hemolytic saponin biosynthesis.

Olive (Olea europaea L.) fruits contain numerous secondary metabolites, primarily phenolics, terpenes and sterols, some of which are particularly interesting for their nutraceutical properties. This study will attempt to provide further insight into the profile of olive phenolic compounds during fruit development and to identify the major genetic determinants of phenolic metabolism.

The secoiridoids are the main class of specialized metabolites present in olive (Olea europaea L.) fruit. In particular, the secoiridoid oleuropein strongly influences olive oil quality because of its bitterness, which is a desirable trait. In addition, oleuropein possesses a wide range of pharmacological properties, including antioxidant, anti-inflammatory, and anti-cancer activities. In accordance, obtaining high oleuropein varieties is a main goal of molecular breeding programs. Here we use a transcriptomic approach to identify candidate genes belonging to the secoiridoid pathway in olive. From these candidates, we have functionally characterized the olive homologue of iridoid synthase (OeISY), an unusual terpene cyclase that couples an NAD (P)H-dependent 1,4-reduction step with a subsequent cyclization, and we provide evidence that OeISY likely generates the monoterpene scaffold of oleuropein in olive fruits. OeISY, the first pathway gene characterized for this type of secoiridoid, is a potential target for breeding programs in a high value secoiridoid-accumulating species.

Background and Aims Postveraison limitation of canopy photosynthesis delays grape berry ripening and reduces sugar accumulation, thus lowering the alcohol content of the subsequent wines. This study was designed to evaluate whether similar results could be obtained by defoliation apical to the bunch zone using a leaf-plucking machine when berry sugar content was approximately 16–17°Brix. Methods and Results In 2011 and 2012, defoliation treatments were applied postveraison to cv. Sangiovese vines (D) on either side of each row using a mechanical leaf remover, and these D vines were compared to a nondefoliated control (C). The machine removed 35% of the leaves on the vine and created a 50-cm vertical window without leaves above the bunch area, but retained a few leaves at the canopy apex (about 0.50 m²/vine). In both years, leaf removal reduced the rate of berry sugar accumulation and led to a 1.2 lower harvest °Brix and consequently, a lower wine alcohol (−0.6%) content in D relative to that of C vines. In 2012, sugar content of D vines, monitored in a group of vines that was not harvested, had recovered to that of C vines 2 weeks after harvest. The concentration of total phenolic compounds in the grapes, the chemical and chromatic characteristics of the wines and the replenishment of soluble sugars, starch and total nitrogen in the canes and roots were similar in the D and C vines. Conclusion To achieve an effective delay in sugar accumulation in the berries, leaves should be removed at 16–17°Brix, and at least 30–35% of vine leaf area should be removed. Significance of the Study Mechanical removal of leaves postveraison above the bunch zone of Sangiovese can be an easy and economically viable technique for delaying sugar accumulation in the berries and for limiting the alcohol content of wines with no negative impact on desirable composition of either berries or wines.

The effectiveness of a postveraison application of the film-forming antitranspirant Vapor Gard (VG, a.i. di-1-p-menthene) was investigated as a technique to delay grape ripening and reduce sugar accumulation in the berry. The study was carried out over the 2010–2011 seasons in a nonirrigated vineyard of cv. Sangiovese in central Italy. Vapor Gard was applied at 2% concentration to the upper two-thirds of the canopy (most functional leaves) and it significantly lowered leaf assimilation and transpiration rates and increased intrinsic water use efficiency. The F_v/F_m ratio was not modified, emphasizing that photoinhibition did not occur at the photosystem II complex, whereas the reduction of pool size of plastoquinone matched well with reduced CO₂ fixation found in VG-treated vines. In both years VG treatment reduced the pace of sugar accumulation in the berry as compared to control vines, scoring a -1.2 Brix at harvest and wine alcohol content at −1% without compromising the recovery of concentrations of carbohydrates and total nitrogen in canes and roots. Concurrently, organic acids, pH, and phenolic richness of grapes and wines were unaffected, whereas there was a decrease in anthocyanin content in the berry (−19% compared to control vines) and in the wine (−15% compared to control vines). The application of VG at postveraison above the cluster zone is an effective, simple, and viable technique to hinder berry sugaring and obtain less alcoholic wines. To be effective the spraying should be performed at ~14 to 15 Brix, making sure that the lower leaf epidermis is fully wetted by the chemical.

Taraxacum kok-saghyz R. (Tks) is a promising alternative species to Hevea brasiliensis for production of high quality natural rubber (NR). A comparative transcriptome analysis of plants with differential production of NR will contribute to elucidate which genes are involved in the synthesis, regulation and accumulation of this natural polymer and could help to develop Tks into a rubber crop. We measured rubber content in the latex of 90 individual Tks plants from 9 accessions, observing a high degree of variability. We carried out de novo root transcriptome sequencing, assembly, annotation and comparison of gene expression of plants with the lower (LR plants) and the higher rubber content (HR plants). The transcriptome analysis also included one plant that did not expel latex, in principle depleted of latex transcripts. Moreover, the transcription of some genes well known to play a major role in rubber biosynthesis, was probed by qRT-PCR. Our analysis showed a high modulation of genes involved in the synthesis of NR between LR and HR plants, and evidenced that genes involved in sesquiterpenoids, monoterpenoids and phenylpropanoid biosynthesis are upregulated in LR plants. Our results show that a higher amount of rubber in the latex in HR plants is positively correlated with high expression levels of a number of genes directly involved in rubber synthesis showing that NR production is highly controlled at transcriptional level. On the other hand, lower amounts of rubber in LR plants is related with higher expression of genes involved in the synthesis of other secondary metabolites that, we hypothesize, may compete towards NR biosynthesis. This dataset represents a fundamental genomic resource for the study of Tks and the comprehension of the synthesis of NR and other biochemically and pharmacologically relevant compounds in the Taraxacum genus.