Seasonal Dynamics and Distribution of Xylella fastidiosa in Infected Almond Trees.

This research focused on studying the dynamics of the bacterial pathogen Xylella fastidiosa in almond trees across different developmental stages. The objective was to understand the seasonal distribution and concentration of X. fastidiosa within almond trees. Different tree organs, including leaves, shoots, branches, fruits, flowers, and roots, from 10 X. fastidiosa-infected almond trees were sampled over 2 years. The incidence and concentration of X. fastidiosa were determined using qPCR and isolation. Throughout the study, X. fastidiosa was consistently absent from fruits, flowers, and roots, whereas it was detected in leaves as well as in shoots and branches. We demonstrate that the absence of X. fastidiosa in the roots is likely linked to the inability of this isolate to infect the peach-almond hybrid rootstock GF677. X. fastidiosa incidence in shoots and branches remained consistent throughout the year, whereas in leaf petioles, it varied across developmental stages, with lower detection during the early and late stages of the season. Similarly, viable X. fastidiosa cells were isolated from shoots and branches at all developmental stages, but no successful isolations were achieved from leaf petioles during the vegetative and nut growth stage. Studying the progression of almond leaf scorch symptoms in trees with initial infections showed that once symptoms emerged on one branch, symptomless branches were likely already infected by the bacterium. Therefore, selectively pruning symptomatic branches is unlikely to cure the tree. This study enhances our understanding of X. fastidiosa dynamics in almond trees and may have practical applications for its detection and control.

Effects of nitrogen fertilization on pomegranate fruit, aril and juice quality.

BACKGROUND: Nitrogen (N) fertilization influences plant growth and yield, and may also affect fruit quality. For two consecutive seasons, we examined the effects of various N fertilization levels - 5 to 200 mg L-1  - on pomegranate fruit, aril and juice quality. Evaluations included fruit and aril weight, size and color, appearance of peel blemishes, internal black rot and nutritional composition of extracted juices. RESULTS: Nitrogen fertilization affected pomegranate fruit, aril and juice quality. The most pronounced effects were observed in trees grown under the lowest N fertilization level, which bore smaller fruit and arils, the latter with lighter color; the fruit suffered from sunburn, and the juice had lower total soluble solid, acidity and anthocyanin contents. The proportion of edible aril weight per total fruit weight gradually increased with an increase in N fertilization concentration. In contrast, N fertilization did not affect peel color, roughness or cracking incidence. Black rot incidence increased with increasing N concentration. CONCLUSIONS: Nitrogen fertilization affected pomegranate fruit, aril and juice quality, and the total number of marketable fruits per tree. The optimal N fertilization levels, which were most beneficial for achieving high-quality marketable fruit, were between 40 and 100 mg L-1 . © 2019 Society of Chemical Industry.

Elucidating the role of shikimate dehydrogenase in controlling the production of anthocyanins and hydrolysable tannins in the outer peels of pomegranate.

BACKGROUND: The outer peels of pomegranate (Punica granatum L.) possess two groups of polyphenols that have health beneficial properties: anthocyanins (ATs, which also affect peel color); and hydrolysable tannins (HTs). Their biosynthesis intersects at 3-dehydroshikimate (3-DHS) in the shikimate pathway by the activity of shikimate dehydrogenase (SDH), which converts 3-DHS to shikimate (providing the precursor for AT biosynthesis) or to gallic acid (the precursor for HTs biosynthesis) using NADPH or NADP+ as a cofactor. The aim of this study is to gain more knowledge about the factors that regulate the levels of HTs and ATs, and the role of SDH. RESULTS: The results have shown that the levels of ATs and HTs are negatively correlated in the outer fruit peels of 33 pomegranate accessions, in the outer peels of two fruits exposed to sunlight, and in those covered by paper bags. When calli obtained from the outer fruit peel were subjected to light/dark treatment and osmotic stresses (imposed by different sucrose concentrations), it was shown that light with high sucrose promotes the synthesis of ATs, while dark at the same sucrose concentration promotes the synthesis of HTs. To verify the role of SDH, six PgSDHs (PgSDH1, PgSDH3-1,2, PgSDH3a-1,2 and PgSDH4) were identified in pomegranate. The expression of PgSDH1, which presumably contributes to shikimate biosynthesis, was relatively constant at different sucrose concentrations. However, the transcript levels of PgSDH3s and PgSDH4 increased with the accumulation of gallic acid and HTs under osmotic stress, which apparently accumulates to protect the cells from the stress. CONCLUSIONS: The results strongly suggest that the biosynthesis of HTs and ATs competes for the same substrate, 3-DHS, and that SDH activity is regulated not only by the NADPH/NADP+ ratio, but also by the expression of the PgSDHs. Since the outer peel affects the customer's decision regarding fruit consumption, such knowledge could be utilized for the development of new genetic markers for breeding pomegranates having higher levels of both ATs and HTs.

Molecular mechanisms involved in postharvest chilling tolerance of pomegranate fruit.

Cold storage of pomegranates is essential for prolonging postharvest storage and for the implementation of cold-quarantine insect disinfestation treatments required for international trading. However, pomegranates are chilling sensitive; they may develop chilling injuries upon exposure to unfavorable low temperatures. In this mini-review, we summarize molecular data obtained from three different RNA Seq transcriptome analyses of responses of pomegranate fruits to cold storage. These experiments included comparisons among the transcriptomic responses following a 2-week exposure to 1 °C in three different model systems: 1) unconditioned chilling-sensitive fruits versus relatively chilling-tolerant low-temperature-conditioned fruits; 2) chilling-sensitive early harvested fruits versus relatively chilling-tolerant late-harvested ones; and 3) chilling-sensitive 'Ganesh' variety versus the relatively chilling-tolerant 'Wonderful' variety. Comparisons among differentially expressed transcripts that were exclusively and significantly up-regulated in the relatively chilling-tolerant fruits in all three model systems enabled identification of 573 common chilling tolerance-associated genes in pomegranates. Functional categorization and classification of the differentially expressed transcripts revealed several regulatory, metabolic, and stress-adaptation pathways that were uniquely activated in response to cold storage in relatively chilling-tolerant fruits. More specifically, we identified common up-regulation of transcripts involved in activation of jasmonic acid and ethylene hormone biosynthesis and signaling, stress-related transcription factors, calcium and MAPK signaling, starch degradation and galactinol and raffinose biosynthesis, phenol biosynthesis, lipid metabolism, and heat-shock proteins. We hypothesized these pathways to be involved in imparting chilling tolerance to pomegranate fruits. © 2019 Society of Chemical Industry.

Characterization of a UGT84 Family Glycosyltransferase Provides New Insights into Substrate Binding and Reactivity of Galloylglucose Ester-Forming UGTs.

Galloylated plant specialized metabolites play important roles in plant-environment interactions and in the promotion of human and animal health. The galloylation reactions are mediated by the formation of galloylglucose esters from gallic acid and UDP-glucose, catalyzed by the plant UGT84 family glycosyltransferases. To explore and exploit the structural determinants of UGT84 activities, we performed homology modeling and substrate docking of PgUGT84A23, a galloylglucose ester-forming family 84 UGT, as well as sequence comparisons of PgUGT84A23 with other functionally characterized plant UGTs. By employing site-directed mutagenesis of candidate amino acids, enzyme assays with analogous substrates, and kinetic analysis, we elucidated key amino acid sites for PgUGT84A23 substrate binding and reactivity. The galloylglucose ester-forming UGT84s have not been shown to glycosylate genistein (an isoflavonoid) in vivo. Unexpectedly, amino acids highly conserved among UGT84s that affect specifically the binding of genistein but not gallic acid or other tested sugar acceptors were identified. This result suggests that genistein may resemble the substrate profile for the enzyme ancestor of the galloylglucose ester-forming UGTs and recruited during transition from a general to a more specialized defense function. Overall, a better understanding of the structure-function relationship of UGT84s will facilitate enzyme engineering for the production of pharmaceutically and industrially valuable glycosylated compounds.

The Pomegranate Deciduous Trait Is Genetically Controlled by a PgPolyQ-MADS Gene.

The pomegranate (Punica granatum L.) is a deciduous fruit tree that grows worldwide. However, there are variants, which stay green in mild winter conditions and are determined evergreen. The evergreen trait is of commercial and scientific importance as it extends the period of fruit production and provides opportunity to identify genetic functions that are involved in sensing environmental cues. Several different evergreen pomegranate accessions from different genetic sources grow in the Israeli pomegranate collection. The leaves of deciduous pomegranates begin to lose chlorophyll during mid of September, while evergreen accessions continue to generate new buds. When winter temperature decreases 10°C, evergreen variants cease growing, but as soon as temperatures arise budding starts, weeks before the response of the deciduous varieties. In order to understand the genetic components that control the evergreen/deciduous phenotype, several segregating populations were constructed, and high-resolution genetic maps were assembled. Analysis of three segregating populations showed that the evergreen/deciduous trait in pomegranate is controlled by one major gene that mapped to linkage group 3. Fine mapping with advanced F3 and F4 populations and data from the pomegranate genome sequences revealed that a gene encoding for a putative and unique MADS transcription factor (PgPolyQ-MADS) is responsible for the evergreen trait. Ectopic expression of PgPolyQ-MADS in Arabidopsis generated small plants and early flowering. The deduced protein of PgPolyQ-MADS includes eight glutamines (polyQ) at the N-terminus. Three-dimensional protein model suggests that the polyQ domain structure might be involved in DNA binding of PgMADS. Interestingly, all the evergreen pomegranate varieties contain a mutation within the polyQ that cause a stop codon at the N terminal. The polyQ domain of PgPolyQ-MADS resembles that of the ELF3 prion-like domain recently reported to act as a thermo-sensor in Arabidopsis, suggesting that similar function could be attributed to PgPolyQ-MADS protein in control of dormancy. The study of the evergreen trait broadens our understanding of the molecular mechanism related to response to environmental cues. This enables the development of new cultivars that are better adapted to a wide range of climatic conditions.

Physiological characterization of the wild almond Prunus arabica stem photosynthetic capability.

Leaves are the major plant tissue for transpiration and carbon fixation in deciduous trees. In harsh habitats, atmospheric CO2 assimilation via stem photosynthesis is common, providing extra carbon gain to cope with the detrimental conditions. We studied two almond species, the commercial Prunus dulcis cultivar "Um-el-Fahem" and the rare wild Prunus arabica. Our study revealed two distinctive strategies for carbon gain in these almond species. While, in P. dulcis, leaves possess the major photosynthetic surface area, in P. arabica, green stems perform this function, in particular during the winter after leaf drop. These two species' anatomical and physiological comparisons show that P. arabica carries unique features that support stem gas exchange and high-gross photosynthetic rates via stem photosynthetic capabilities (SPC). On the other hand, P. dulcis stems contribute low gross photosynthesis levels, as they are designed solely for reassimilation of CO2 from respiration, which is termed stem recycling photosynthesis (SRP). Results show that (a) P. arabica stems are covered with a high density of sunken stomata, in contrast to the stomata on P. dulcis stems, which disappear under a thick peridermal (bark) layer by their second year of development. (b) P. arabica stems contain significantly higher levels of chlorophyll compartmentalized to a mesophyll-like, chloroplast-rich, parenchyma layer, in contrast to rounded-shape cells of P. dulcis's stem parenchyma. (c) Pulse amplitude-modulated (PAM) fluorometry of P. arabica and P. dulcis stems revealed differences in the chlorophyll fluorescence and quenching parameters between the two species. (d) Gas exchange analysis showed that guard cells of P. arabica stems tightly regulate water loss under elevated temperatures while maintaining constant and high assimilation rates throughout the stem. Our data show that P. arabica uses a distinctive strategy for tree carbon gain via stem photosynthetic capability, which is regulated efficiently under harsh environmental conditions, such as elevated temperatures. These findings are highly important and can be used to develop new almond cultivars with agriculturally essential traits.

A pomegranate (Punica granatum L.) WD40-repeat gene is a functional homologue of Arabidopsis TTG1 and is involved in the regulation of anthocyanin biosynthesis during pomegranate fruit development.

Anthocyanins are the major pigments responsible for the pomegranate (Punica granatum L.) fruit skin color. The high variability in fruit external color in pomegranate cultivars reflects variations in anthocyanin composition. To identify genes involved in the regulation of anthocyanin biosynthesis pathway in the pomegranate fruit skin we have isolated, expressed and characterized the pomegranate homologue of the Arabidopsis thaliana TRANSPARENT TESTA GLABRA1 (TTG1), encoding a WD40-repeat protein. The TTG1 protein is a regulator of anthocyanins and proanthocyanidins (PAs) biosynthesis in Arabidopsis, and acts by the formation of a transcriptional regulatory complex with two other regulatory proteins: bHLH and MYB. Our results reveal that the pomegranate gene, designated PgWD40, recovered the anthocyanin, PAs, trichome and seed coat mucilage phenotype in Arabidopsis ttg1 mutant. PgWD40 expression and anthocyanin composition in the skin were analyzed during pomegranate fruit development, in two accessions that differ in skin color intensity and timing of appearance. The results indicate high positive correlation between the total cyanidin derivatives quantity (red pigments) and the expression level of PgWD40. Furthermore, strong correlation was found between the steady state levels of PgWD40 transcripts and the transcripts of pomegranate homologues of the structural genes PgDFR and PgLDOX. PgWD40, PgDFR and PgLDOX expression also correlated with the expression of pomegranate homologues of the regulatory genes PgAn1 (bHLH) and PgAn2 (MYB). On the basis of our results we propose that PgWD40 is involved in the regulation of anthocyanin biosynthesis during pomegranate fruit development and that expression of PgWD40, PgAn1 and PgAn2 in the pomegranate fruit skin is required to regulate the expression of downstream structural genes involved in the anthocyanin biosynthesis.

Revealing the Genetic Components Responsible for the Unique Photosynthetic Stem Capability of the Wild Almond Prunus arabica (Olivier) Meikle.

Almond [Prunus dulcis (Mill.) D. A. Webb] is a major deciduous fruit tree crop worldwide. During dormancy, under warmer temperatures and inadequate chilling hours, the plant metabolic activity increases and may lead to carbohydrate deficiency. Prunus arabica (Olivier) Meikle is a bushy wild almond species known for its green, unbarked stem, which stays green even during the dormancy period. Our study revealed that P. arabica green stems assimilate significantly high rates of CO2 during the winter as compared to P. dulcis cv. Um el Fahem (U.E.F.) and may improve carbohydrate status throughout dormancy. To uncover the genetic inheritance and mechanism behind the P. arabica stem photosynthetic capability (SPC), a segregated F1 population was generated by crossing P. arabica to U.E.F. Both parent's whole genome was sequenced, and SNP calling identified 4,887 informative SNPs for genotyping. A robust genetic map for U.E.F. and P. arabica was constructed (971 and 571 markers, respectively). QTL mapping and association study for the SPC phenotype revealed major QTL [log of odd (LOD) = 20.8] on chromosome 7 and another minor but significant QTL on chromosome 1 (LOD = 3.9). As expected, the P. arabica allele in the current loci significantly increased the SPC phenotype. Finally, a list of 64 candidate genes was generated. This work sets the stage for future research to investigate the mechanism regulating the SPC trait, how it affects the tree's physiology, and its importance for breeding new cultivars better adapted to high winter temperatures.

Fine Mapping of the "black" Peel Color in Pomegranate (Punica granatum L.) Strongly Suggests That a Mutation in the Anthocyanidin Reductase (ANR) Gene Is Responsible for the Trait.

Anthocyanins are important dietary and health-promoting substances present in high quantities in the peel and arils of the pomegranate (Punica granatum L.) fruit. Yet, there is a high variation in the content of anthocyanin among different pomegranate varieties. The 'Black' pomegranate variety (P.G.127-28) found in Israel contains exceptionally high levels of anthocyanins in its fruit peel which can reach up to two orders of magnitude higher content as compared to that of other pomegranate varieties' peel anthocyanins. Biochemical analysis reveals that delphinidin is highly abundant in the peel of 'Black' variety. The pattern of anthocyanin accumulation in the fruit peel during fruit development of 'Black' variety differs from that of other pomegranates. High anthocyanin levels are maintained during all developmental stages. Moreover, the accumulation of anthocyanin in the fruit peel of 'Black' variety is not dependent on light. Genetic analysis of an F2 population segregating for the "black" phenotype reveals that it is determined by a single recessive gene. Genetic mapping of the F2 population using single nucleotide polymorphism (SNP) markers identified few markers tightly linked to the "black" phenotype. Recombination analysis of the F2 population and F3 populations narrowed the "black" trait to an area of 178.5 kb on the draft genome sequence of pomegranate cv. 'Dabenzi.' A putative anthocyanidin reductase (ANR) gene is located in this area. Only pomegranate varieties displaying the "black" trait carry a base pair deletion toward the end of the gene, causing a frame shift resulting in a shorter protein. We propose that this mutation in the ANR gene is responsible for the different anthocyanin composition and high anthocyanin levels of the "black" trait in pomegranate.

Pedigree analysis of 220 almond genotypes reveals two world mainstream breeding lines based on only three different cultivars.

Loss of genetic variability is an increasing challenge in tree breeding programs due to the repeated use of a reduced number of founder genotypes. However, in almond, little is known about the genetic variability in current breeding stocks, although several cases of inbreeding depression have been reported. To gain insights into the genetic structure in modern breeding programs worldwide, marker-verified pedigree data of 220 almond cultivars and breeding selections were analyzed. Inbreeding coefficients, pairwise relatedness, and genetic contribution were calculated for these genotypes. The results reveal two mainstream breeding lines based on three cultivars: "Tuono", "Cristomorto", and "Nonpareil". Descendants from "Tuono" or "Cristomorto" number 76 (sharing 34 descendants), while "Nonpareil" has 71 descendants. The mean inbreeding coefficient of the analyzed genotypes was 0.041, with 14 genotypes presenting a high inbreeding coefficient, over 0.250. Breeding programs from France, the USA, and Spain showed inbreeding coefficients of 0.075, 0.070, and 0.037, respectively. According to their genetic contribution, modern cultivars from Israel, France, the USA, Spain, and Australia trace back to a maximum of six main founding genotypes. Among the group of 65 genotypes carrying the Sf allele for self-compatibility, the mean relatedness coefficient was 0.125, with "Tuono" as the main founding genotype (24.7% of total genetic contribution). The results broaden our understanding about the tendencies followed in almond breeding over the last 50 years and will have a large impact into breeding decision-making process worldwide. Increasing current genetic variability is required in almond breeding programs to assure genetic gain and continuing breeding progress.

Glutathione peroxidase regulation of reactive oxygen species level is crucial for in vitro plant differentiation.

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is overexpressed in plants under abiotic and biotic stress conditions that mediate oxidative stress. To study its biological role and its ability to confer stress resistance in plants, we tried to obtain transgenic plants overexpressing citrus (Citrus sinensis) PHGPx (cit-PHGPx). All attempts to obtain regenerated plants expressing this enzyme constitutively failed. However, when the enzyme's catalytic activity was abolished by active site-directed mutagenesis, transgenic plants constitutively expressing inactive cit-PHGPx were successfully regenerated. Constitutive expression of enzymatically active cit-PHGPx could only be obtained when transformation was based on non-regenerative processes. These results indicate that overexpression of the antioxidant enzyme PHGPx interferes with shoot organogenesis and suggests the involvement of reactive oxygen species (ROS) in this process. Using transgenic tobacco (Nicotiana tabacum) leaves obtained from plants transformed with a beta-estradiol-inducible promoter, time-dependent induction of cit-PHGPx expression was employed. A pronounced inhibitory effect of cit-PHGPx on shoot formation was found to be limited to the early stage of the regeneration process. Monitoring the ROS level during regeneration revealed that upon cit-PHGPx induction, the lowest level of ROS correlated with the maximal level of shoot inhibition. Our results clearly demonstrate the essential role of ROS in the early stages of in vitro shoot organogenesis and the possible involvement of PHGPx in maintaining ROS homeostasis at this point.

Mapping quantitative trait loci associated with chilling requirement, heat requirement and bloom date in peach (Prunus persica).

*Chilling requirement, together with heat requirement, determines the bloom date, which has an impact on the climatic distribution of the genotypes of tree species. The molecular basis of floral bud chilling requirement is poorly understood, despite its importance to the adaptation and production of fruit trees. In addition, the genetic nature of heat requirement and the genetic interrelationships among chilling requirement, heat requirement and bloom date remain unclear. *A peach (Prunus persica) F(2) population of 378 genotypes developed from two genotypes with contrasting chilling requirements was used for linkage map construction and quantitative trait loci (QTL) mapping. The floral bud chilling and heat requirements of each genotype were evaluated over 2 yr and the bloom date was scored over 4 yr. *Twenty QTLs with additive effects were identified for three traits, including one major QTL for chilling requirement and two major QTLs for bloom date. The majority of QTLs colocalized with QTLs for other trait(s). In particular, one genomic region of 2 cM, pleiotropic for the three traits, overlapped with the sequenced peach EVG region. *This first report on the QTL mapping of floral bud chilling requirement will facilitate marker-assisted breeding for low chilling requirement cultivars and the map-based cloning of genes controlling chilling requirement. The extensive colocalization of QTLs suggests that there may be one unified temperature sensing and action system regulating chilling requirement, heat requirement and bloom date together.

Genetic linkage mapping for molecular dissection of chilling requirement and budbreak in apricot (Prunus armeniaca L.).

Commercial production of apricot is severely affected by sensitivity to climatic conditions, an adaptive feature essential for cycling between vegetative or floral growth and dormancy. Yield losses are due to late winter or early spring frosts and inhibited vegetative or floral growth caused by unfulfilled chilling requirement (CR). Two apricot cultivars, Perfection and A.1740, were selected for high and low CR, respectively, to develop a mapping population of F1 individuals using a two-way pseudo-testcross mapping strategy. High-density male and female maps were constructed using, respectively, 655 and 592 markers (SSR and AFLP) spanning 550.6 and 454.9 cM with average marker intervals of 0.84 and 0.77 cM. CR was evaluated in two seasons on potted trees forced to break buds after cold treatments ranging from 100 to 900 h. A total of 12 putative CR quantitative trait loci (QTLs) were detected on six linkage groups using composite interval mapping and a simultaneous multiple regression fit. QTL main effects of additive and additive x additive interactions accounted for 58.5% +/- 6.7% and 66.1% +/- 5.8% of the total phenotypic variance in the Perfection and A.1740 maps, respectively. We report two apricot high-density maps and QTLs corresponding to map positions of differentially expressed transcripts and suggested candidate genes controlling CR.

Primary Metabolites, Anthocyanins, and Hydrolyzable Tannins in the Pomegranate Fruit.

Pomegranate (Punica granatum L.) is an important and interesting fruit tree that is cultivated in many parts of the world. In recent years, along with the increase in its cultivation and consumption there has been a dramatic increase in the scientific interest in its biology, methods of cultivation, adaptation to environmental cues and its health-promoting properties. Quite a large proportion of the various metabolites produced in the pomegranate were determined and their content in the bark, roots, leaves, and fruit was reported. Many reviews on polyphenolic compound content, antioxidant activity and health-promoting compounds were published recently. However, only very few recent reports were dedicated to primary metabolites, despite the fact that much work was done on organic acids, sugars, proteins, lipids, and amino acids of the pomegranate fruit. In this review, a special effort was made to present these recent studies and the review is devoted to primary metabolites. The reported data show high variation in the content of primary metabolites within the pomegranate fruit; therefore the data is presented (whenever possible) according to fruit tissues (peel, arils, and seeds), developmental stages of the fruit, environmental and climatic conditions, and genetic background. Most of the data on pomegranate is based on metabolic content and contains no genetic or molecular analysis except for work done on anthocyanins and hydrolyzable tannins. In those cases, gene assignment and genetic control studies were pointed out in the review. The recent publication of the genome sequences from several pomegranate varieties and transcriptomic data from fruits, flowers, and leaves is expected to facilitate the understanding of genetic control of metabolites in pomegranate.

Profiling of volatile terpenes from almond (Prunus dulcis) young fruits and characterization of seven terpene synthase genes.

Almond (Prunus dulcis) is an agricultural and economically important fruit tree from the Rosaceae family used in the food industry. The monoterpenes and sesquiterpenes perform important ecological functions such as insecticidal and antifeedant activities against various insects. The young fruits of the different almond varieties were found to produce considerable amounts of terpene volatiles, including linalool and geraniol. To identify terpene synthases (TPSs) involved in the production of these volatile terpenes, existing genome databases of the Rosaceae were screened for almond genes with significant sequence similarity to other plants TPSs. Bioinformatics analysis led to the identification of seven putative TPSs genes with complete open reading frames. We characterized the enzymes encoded by these seven complementary DNAs: the monoterpene synthases PdTPS1, PdTPS3, PdTPS5, and PdTPS6 belong to the TPS-b clade, which catalyzes the formation of ß-phellandrene, geraniol, linalool, and farnesene, respectively. The sesquiterpene synthases PdTPS2 and PdTPS4, which belong to the TPS-a clade mainly catalyze the formation of bergamotene, while another sesquiterpene synthase, PdTPS7, from the TPS-g clade showed nerolidol synthase activity. The qRT-PCR analysis revealed that the various tissues of almond varieties showed differential transcription for all these PdTPSs genes.

A Pyrus communis gene for p-hydroxystyrene biosynthesis, has a role in defense against the pear psylla Cacopsylla biden.

Styrene analogs are known to be naturally synthesized in the leaves of pears and in other plant species, including several trees in the Styracaceae family. Styrene analogs are potential contributors to the aroma of wine, perfumes, pharmaceuticals, and other fermented foods and beverages. In addition, styrene analogs perform important ecological functions such as insecticidal and antifeedant activities against insects. We showed here that exogenous applications of styrene and p-hydroxystyrene caused a dramatic reduction the number of eggs laid by psylla and of subsequent nymph survival. Despite their importance specific reactions that lead to the biosynthesis of the styrene analogs in pear are unknown. To identify genes involved in the synthesis of these metabolites, existing genome databases of the Rosaceae were screened for pear genes with significant sequence similarity to bacterial phenolic acid decarboxylase. Herein described are the isolation and characterization of a pear phenolic acid decarboxylase, designated PyPAD1, which catalyzed the decarboxylation of p-coumaric acid and ferulic acid to p-hydroxystyrene and 3-methoxy-4-hydroxystyrene respectively. Its apparent Km values for p-coumaric acid and ferulic acid were 34.42 and 84.64 µM, respectively. The PyPAD1 preferred p-coumaric acid to ferulic acid as a substrate by a factor of 2.4 when comparing catalytic efficiencies in vitro. Expression analysis of PyPAD1 showed that the gene was transcribed in all five pear genotypes examined. However, transcript abundance was increased in correlation with the presence of p-hydroxystyrene in resistant cultivars Py-701 and Py-760 and in the sensitive cultivar Spadona when grafted on these resistant cultivars. Thus, PyPAD1 appears to be responsible for the decarboxylation of the p-coumaric acid, and for the production of metabolites that are active against pear psylla.

Diversity among Pomegranate Varieties in Chilling Tolerance and Transcriptome Responses to Cold Storage.

We found great variability in chilling tolerance among 84 pomegranate varieties from the Newe Ya'ar collection; among them, 'Ganesh' was chilling-sensitive, whereas 'Wonderful' was relatively chilling-tolerant. To evaluate the different molecular responses of these varieties to cold storage, we analyzed the transcriptomic changes in the inner membrane tissues of 'Ganesh' and 'Wonderful' fruit after 2 weeks of cold storage at 1 °C. By functional categorization of the differentially expressed transcripts using MapMan, we found that many transcripts related to various pathways, such as jasmonic acid biosynthesis and signaling, galactinol, raffinose, phenol, and phenylpropanoid biosynthesis, calcium and mitogen-activated protein kinase signaling, lipid metabolism, and various transcription factors and heat-shock proteins, have been massively upregulated in 'Wonderful' but not in 'Ganesh' fruit. Thus, it is suggested that these pathways most likely participate in imparting chilling tolerance in pomegranate fruit.

Grafting on resistant interstocks reduces scion susceptibility to pear psylla, Cacopsylla bidens.

BACKGROUND: Pear psylla is a major obstacle to efficient integrated pest management in pear orchards in Israel and around the world. We used two accessions with natural resistance to pear psylla Cacopsylla bidens (Sulc) - Py.760-261 (760) and Py.701-202 (701), both apparently of Pyrus communis L. origin - as interstock grafts to confer psylla resistance to the commercially important 'Spadona Estiva' (Pyrus communis) scion (Spadona) cultivar. The interaction of the interstocks with quince (Cydonia oblong Mill.) and Pyrus betulifolia Bunge rootstocks was also tested. RESULTS: Usage of Py.760-261 (760) and Py.701-202 (701) as interstocks for the psylla-sensitive Spadona resulted in a five-fold decrease in the C. bidens population, apparently as a consequence of antibiosis affecting nymph survival. Additionally, psylla survival was negatively correlated with the interstock length and amount of foliage. The yield and fruit quality of Spadona grafted on the '701' interstock equaled or even exceeded those of the control in fruit quantity, fruit size and soluble solids content, especially on P. betulifolia rootstock. CONCLUSION: Susceptibility to pear psylla decreased significantly following grafting of commercial Spadona on resistant interstock. This is the first demonstration of increased resistance to pear psylla conferred by the use of resistant interstock in pear trees and among the few examples demonstrating transfer of resistance to insects from the interstock in fruit trees. © 2017 Society of Chemical Industry.

Antioxidant activity, polyphenol content, and related compounds in different fruit juices and homogenates prepared from 29 different pomegranate accessions.

Pomegranate juice is well known for its health beneficial compounds, which can be attributed to its high level of antioxidant activity and total polyphenol content. Our objective was to study the relationships between antioxidant activity, total polyphenol content, total anthocyanins content, and the levels of four major hydrolyzable tannins in four different juices/homogenates prepared from different sections of the fruit. To this end, 29 different accessions were tested. The results showed that the antioxidant activity in aril juice correlated significantly to the total polyphenol and anthocyanin contents. However, the homogenates prepared from the whole fruit exhibited an approximately 20-fold higher antioxidant activity than the level found in the aril juice. Unlike the arils, the antioxidant level in the homogenates correlated significantly to the content of the four hydrolyzable tannins in which punicalagin is predominant, while no correlation was found to the level of anthocyanins.