A systematic study to determine the extent of gene silencing in Nicotiana benthamiana and other Solanaceae species when heterologous gene sequences are used for virus-induced gene silencing

Virus-induced gene silencing (VIGS) is a rapid and robust method for determining and studying the function of plant genes or expressed sequence tags (ESTs). However, only a few plant species are amenable to VIGS. There is a need for a systematic study to identify VIGS-efficient plant species and to determine the extent of homology required between the heterologous genes and their endogenous orthologs for silencing. Two approaches were used. First, the extent of phytoene desaturase (PDS) gene silencing was studied in various Solanaceous plant species using Nicotiana benthamiana NbPDS sequences. In the second approach, PDS sequences from a wide range of plant species were used to silence the PDS gene in N. benthamiana. The results showed that tobacco rattle virus (TRV)-mediated VIGS can be performed in a wide range of Solanaceous plant species and that heterologous gene sequences from far-related plant species can be used to silence their respective orthologs in the VIGS-efficient plant N. benthamiana. A correlation was not always found between gene silencing efficiency and percentage homology of the heterologous gene sequence with the endogenous gene sequence. It was concluded that a 21-nucleotide stretch of 100% identity between the heterologous and endogenous gene sequences is not absolutely required for gene silencing.     

Colored shading nets impede insect invasion and decrease the incidences of insect‐transmitted viral diseases in vegetable crops

Black shading nets are commonly used to protect agricultural crops from excessive solar radiation and wind, and for water saving. Recent studies have demonstrated that when black nets were replaced by either red, yellow, or pearl nets (ChromatiNets^?) of equivalent shading capacity, it increased the fruit yield and improved the quality of bell peppers (Capsicum annuum L.) and tomatoes (Solanum lycopersicum L.) (both Solanaceae). We studied the effects of these colored shading nets on the infestation by aphids [Myzus persicae (Sulzer) and Aphis gossypii Glover (both Hemiptera: Aphididae)] and whiteflies [Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae)], and the incidence of the viral diseases transmitted by these insects, for five consecutive years (2006–2010). These studies were conducted in the semi‐arid Besor region in southern Israel. The plants were grown in ‘walk‐in’ tunnels that were covered by several nets of 35% shading capacity in the range of photosynthetically active radiation. Although the shading nets permit free passage of these pests, the infestation levels of aphids and whiteflies in tunnels covered by either the yellow or pearl nets were consistently 2–3× lower than in tunnels covered by the black or red nets. In accordance with the pest results, when the incidences of Cucumber mosaic virus in pepper grown under the black or red nets ranged between 35 and 89%, they were 2–10× lower under the yellow or pearl nets. Similarly, when the incidences of necrotic Potato virus Y in tomato grown under black or red nets ranged between 42 and 50%, they were 2–3× lower under the yellow or pearl nets. Also, when the incidences of Tomato yellow leaf curl virus in tomato grown under the black or red nets ranged between 15 and 50%, but they were 2–4× lower under the yellow or pearl nets. Putative mechanisms of crop protection achieved by the yellow and pearl nets are discussed.     

Niche-based prediction of establishment of biocontrol agents: an example with Gratiana boliviana and tropical soda apple

Successful establishment of a biological control agent is a prerequisite for effective reduction of an invasive weed. Niche-based species distribution models can generate valuable information about the potential spread of a biological control agent and help to predict its distribution. The Maximum Entropy Species Distribution Model was used in our study to predict distributions of the leaf beetle Gratiana boliviana Spaeth (Coleoptera: Chrysomelidae) and its target weed, tropical soda apple (TSA), Solanum viarum Dunal (Solanaceae). The specific objectives of this study were to (1) assess the climatic suitability for establishment of this insect across the invasive range of the weed by overlapping predicted current distributions and, (2) examine the niche-related restriction in distribution of the insect by visualising the predictive niche in multivariate space. Accuracy of predicted distributions was tested using binomial tests and area under the curve scores. The results of statistical tests confirmed that the predictions were significantly better than random. The predictions indicated that the potential distribution of G. boliviana in the USA will be more restricted than that of its host plant. Consequently, the beetle's ability to inflict damage to TSA will be geographically limited. Niche visualisation, using a PCA-based analysis, provided evidence of the niche imposed restriction on the distribution of G. boliviana. Overall, this study proposes a new approach for understanding the spatial limitations in establishment of biological control agents, allowing researchers to establish more realistic expectations of success.     

Dyssochroma viridiflorum (Solanaceae): a reproductively bat-dependent epiphyte from the Atlantic rainforest in Brazil

Few Neotropical plant species seem to depend on the same animal type both for pollination and seed dispersal, and the known instances refer mostly to birds as the agents in these two phases of a plant reproductive cycle. Dyssochroma viridiflorum (Solanaceae), an epiphyte endemic to the Atlantic rainforest in south-eastern Brazil, was found to be visited by phyllostomid bats for nectar as well as for fruits, with the pollination and seed dispersal of the plant ensured by these flying mammals. The greenish flowers open at night and are visited by the nectar-feeding bat Glossophaga soricina, whereas the yellowish-white fruits are consumed by two species of fruit-eating bats, Carollia perspicillata and Sturnira lilium. Only clinging visits, an uncommon behavioural pattern for glossophagine bats while feeding on flowers, were recorded. The small seeds of D. viridiflorum are swallowed along with the fruit pulp and later defecated on the bats' flying pathways. It is suggested that species of Dyssochroma and two other solanaceous bat-pollinated genera, Merinthopodium and Trianaea, form a derived and bat-dependent clade within the Juanulloeae.     

Archaeobotanic evidence of the preincaic Chiribaya culture. Determination of capsaicinoids in archaeological samples of Capsicum frutescens and votive foods

The lack of Capsicum species or paprika (a basic ingredient of Peruvian foodstuff) in preincaic archaeological samples and votive foods, as evidenced by archaeobotanic studies, has stimulated the chemical analyses of these samples by HPLC methods. The results confirmed the absence of capsaicinoids in these samples whereas they were detected in more ancient fossil fruit.     

Early steps of deoxyxylulose phosphate pathway in chromoplasts of higher plants

1-Deoxy-D-xylulose 5-phosphate and 2C-methyl-D-erythritol 4-phosphate have been shown as intermediates of the deoxyxylulose phosphate pathway used for terpenoid biosynthesis in plants and many microorganisms. In plants this non-mevalonate pathway is located in plastids. In order to investigate the formation of five carbon intermediates, chromoplasts from Capsicum annuum and Narcissus pseudonarcissus were incubated with isotope-labeled 1-deoxy-D-xylulose 5-phosphate or 2C-methyl-D-erythritol 4-phosphate. The downstream metabolites were detected and separated by reversed-phase ion-pair radio-HPLC and their structures elucidated by mass spectroscopy. Here we report the isolation and structural identification of 4-diphosphocytidyl-2C-methyl-D-erythritol and 2C-methyl-D-erythritol 2,4-cyclodiphosphate from chromoplasts; the genes of the corresponding enzymes had been previously identified from Escherichia coli and Arabidopsis.     

Two acyl sucroses from Petunia nyctaginiflora

Two new acyl sucroses were isolated from the epigeal parts of Petunia nyctaginiflora Juss. (Solanaceae). Their structures were determined to be 2, 3, 4-tri (5-methylhexanoyl)-alpha-D-glucopyranosyl-beta-D-fructofuranoside (2) and 2, 3, 4-tri (6-methylheptanoyl)-alpha-D-glucopyranosyl-beta-D-fructofuranoside (4) on the basis of chemical and spectroscopic evidence.     

Differences in nucleotide-binding site of isoapyrases deduced from tryptophan fluorescence

Comparative studies of intrinsic and extrinsic fluorescence of apyrases purified from two potato tuber varieties (Pimpernel and Desirée) were performed to determine differences in the microenvironment of the nucleotide binding site. The dissociation constants (K(d)) of Pimpernel apyrase for the binding of different fluorescent substrate analogs: methylanthranoyl (MANT-), trinitrophenyl (TNP-), and epsilon -derivatives of ATP and ADP were determined from the quenching of Trp fluorescence, and compared with K(d) values previously reported for Desirée enzyme. Binding of non-fluorescent substrate analogues decreased the Trp emission of both isoapyrases, indicating conformational changes in the vicinity of these residues. Similar effect was observed with fluorescent derivatives where, in the quenching effect, the transfer of energy from tryptophan residues to the fluorophore moiety could be additionally involved. The existence of energy transfer between Trp residues in the Pimpernel enzyme was demonstrated with epsilon -analogues, similar to our previous observations with the Desirée. From these results we deduced that tryptophan residues are close to or in the nucleotide binding site in both enzymes. Experiments with quenchers like acrylamide, Cs(+) and I(-), both in the presence and absence of nucleotide analogues, suggest the existence of differences in the nucleotide binding site of the two enzymes. From the results obtained in this work, we can conclude that the differences found in the microenvironment of the nucleotide binding site can explain, at least in part, the kinetic behaviour of both isoenzymes.     

QTLs involved in the restriction of cucumber mosaic virus (CMV) long-distance movement in pepper

Partial restriction of cucumber mosaic virus (CMV) long-distance movement originating from the Capsicum annuum inbred line ’Vania’ was assessed in a doubled-haploid progeny using two screening methods: the first allowed one to assess the resistance of adult plants decapitated above the fourth leaf and inoculated on the third leaf using a common CMV strain, and the second allowed one to assess CMV resistance to long-distance movement on seedlings inoculated using an atypical CMV strain. For both resistance tests, the behavior of the F₁ hybrid between ’Vania’ and the susceptible line ’H3’ indicated that partial resistance is inherited as a dominant trait. Phenotypic data from the two screening methods were correlated but the one performed on seedlings was much more severe. A subset of 184 molecular markers well-distributed over the pepper genome was selected for QTL mapping using the composite interval mapping (CIM) method. A total of seven genomic regions, including one major effect and several minor effect QTLs, were shown to be associated with partial restriction of CMV long-distance movement. These results are compared with those already obtained in pepper and also in other solanaceous crops, potato and tomato. Received: 22 March 2001 / Accepted: 9 July 2001     

Melongosides n,o and p: steroidal saponins from seeds of solanum melongena

Three new saponins, melongosides N, O and P, have been isolated from the methanolic extract of seeds of Solanum melongena and their structures elucidated. Melongoside N is 3-O-[β-D-glucopyranosy l-(1 → 2)-β-D-glucopyranosyl]-26-O-(β-D-glucopyranosyl)-(25R)-5α-furostan-3β,22 α,26-triol, whereas melongoside O is 3-O-[β-D-glucopyranosyl-(1 → 2)β-D-glucopyranosyl]- 26-O-(β-D-glucopyranosyl)-(25R)-furost-5-en-3β,22α,26-triol and melongoside P is 3-O- [β-D-glucopyranosyl-(1 → 2)]-[α-L-rhamnopyranosyl-(1 → 3)]-β-D-glucopyranosyl)-26-O- (β-D-glucopyranosyl)-(25 R)-5α-furostan-3β,22α,26-triol.