Patrick du Jardin

Attacks by a piercing-sucking insect (Myzus persicae Sultzer) or a chewing insect (Leptinotarsa decemlineata Say) on potato plants (Solanum tuberosum L.) induce differential changes in volatile compound release and oxylipin synthesis

Plant defensive strategies bring into play blends of compounds dependent on the type of attacker and coming from different synthesis pathways. Interest in the field is mainly focused on volatile organic compounds (VOCs) and jasmonic acid (JA). By contrast, little is known about the oxidized polyunsaturated fatty acids (PUFAs), such as PUFA-hydroperoxides, PUFA-hydroxides, or PUFA-ketones. PUFA-hydroperoxides and their derivatives might be involved in stress response and show antimicrobial activities. Hydroperoxides are also precursors of JA and some volatile compounds. In this paper, the differential biochemical response of a plant against insects with distinct feeding behaviours is characterized not only in terms of VOC signature and JA profile but also in terms of their precursors synthesized through the lipoxygenase (LOX)-pathway at the early stage of the plant response. For this purpose, two leading pests of potato with distinct feeding behaviours were used: the Colorado Potato Beetle (Leptinotarsa decemlineata Say), a chewing herbivore, and the Green Peach Aphid (Myzus persicae Sulzer), a piercing-sucking insect. The volatile signatures identified clearly differ in function with the feeding behaviour of the attacker and the aphid, which causes the smaller damages, triggers the emission of a higher number of volatiles. In addition, 9-LOX products, which are usually associated with defence against pathogens, were exclusively activated by aphid attack. Furthermore, a correlation between volatiles and JA accumulation and the evolution of their precursors was determined. Finally, the role of the insect itself on the plant response after insect infestation was highlighted.

Role of terpenes from aphid‐infested potato on searching and oviposition behavior of Episyrphus balteatus

To cope with pathogen and insect attacks, plants develop different mechanisms of defence, in both direct (physical and chemical) and indirect ways (attractive volatiles to entomophagous beneficials). Plants are then able to express traits that facilitate “top‐down” control of pests by attracting herbivore predators. Here we investigate the indirect defence mechanism of potato plants by analyzing the volatile patterns of both healthy and aphid‐infested plants. Important changes in the emitted terpene pattern by the Myzus persicae infested host plant were observed. Using Solid Phase Micro Extraction (SPME) and GC‐MS, the (E)‐β‐farnesene (EBF) appeared to be emitted by aphid‐infested potato and not by healthy plants. To assess the infochemical role of these volatile releases after aphid damage on the aphidophagous predators Episyrphus balteatus, the hoverfly foraging behavior was assessed using the Observer 5.0 software (Noldus, Wageningen, The Netherlands). Aphid‐free potato plants were also used as a control volatile source in the predator behavioral study. While aphid‐infested plants induced efficient searching and acceptation behaviors leading to egg‐laying, no kairomonal effect of healthy potato plants was observed, leading to longer immobility durations and shorter searching periods in the net cage. High oviposition rate of E. balteatus was observed when aphid‐infested potato was used (mean of 48.9 eggs per laying and per female). On the other hand, no egg was produced by the hoverfly on healthy aphid‐free plants. The E. balteatus foraging and reproductive behaviors according to the volatile emission from aphid‐infested plants are discussed in relation to the potential use of active infochemical molecules in integrated aphid pest management.

Genetic Diversity In Lima Bean (Phaseolus Lunatus L) As Revealed By Rapd Markers

The genetic variability of 46 accessions of the Lima bean (P. lunatus L.) including 16 wild forms and 30 landraces belonging to the three cultigroups Big lima, Sieva, Potato, and their intermediates, was evaluated using RAPD (Random amplified polymorphic DNA) markers. Twelve oligonucleotide primers produced 172 RAPD markers which allowed the differentiation of two main groups: the mesoamerican and the andean groups. This was confirmed by an AMOVA analysis which indicated that 37.7% of the variation was found between these two groups. For each botanical form (wild and cultivated), the molecular markers showed that small-seeded types (i.e. Sieva and Potato types and their related wild forms) had a wide distribution (from Mexico to Argentina) while the large-seeded types (Big lima type and its related wild forms) were circumscribed to the narrow west-coastal region from Ecuador to Bolivia. The results are in favour of an independent domestication process within the two groups, as the differentiation between mesoamerican and andean accessions was found to occur in both wild forms and landraces. Within each of the two main groups, wild forms and landraces were also found to be genetically differentiated and higher genetic diversity was observed among landraces than among wild forms. Within the mesoamerican landraces, low but significant differentiation between the Sieva and Potato cultigroups was observed. Some suggestions and hypotheses are discussed about evolution of the two small-seeded types.

Potato (Solanum tuberosum L.) tuber ageing induces changes in the proteome and antioxidants associated with the sprouting pattern.

During post-harvest storage, potato tubers age as they undergo an evolution of their physiological state influencing their sprouting pattern. In the present study, physiological and biochemical approaches were combined to provide new insights on potato (Solanum tuberosum L. cv. Désirée) tuber ageing. An increase in the physiological age index (PAI) value from 0.14 to 0.83 occurred during storage at 4 °C over 270 d. Using this reference frame, a proteomic approach was followed based on two-dimensional electrophoresis. In the experimental conditions of this study, a marked proteolysis of patatin occurred after the PAI reached a value of 0.6. In parallel, several glycolytic enzymes were up-regulated and cellular components influencing protein conformation and the response to stress were altered. The equilibrium between the 20S and 26S forms of the proteasome was modified, the 20S form that recycles oxidized proteins being up-regulated. Two proteins belonging to the cytoskeleton were also differentially expressed during ageing. As most of these changes are also observed in an oxidative stress context, an approach focused on antioxidant compounds and enzymes as well as oxidative damage on polyunsaturated fatty acids and proteins was conducted. All the changes observed during ageing seemed to allow the potato tubers to maintain their radical scavenging activity until the end of the storage period as no accumulation of oxidative damage was observed. These data are interpreted considering the impact of reactive oxygen species on the development and the behaviour of other plant systems undergoing ageing or senescence processes.

Molecular Cloning And Characterization Of The Enzyme Udp-Glucose: Protein Transglucosylase From Potato

Abstract UDP-Glc:protein transglucosylase (UPTG) (EC 2.4.1.112) is an autocatalytic glycosyl-transferase previously postulated as a protein that primes starch biosynthesis. Polyclonal antibodies raised against UPTG purified from potato ( Solanum tuberosum L.) tubers were used to screen a potato swelling stolon tip cDNA expression library. The isolation, cloning and sequencing of two cDNAs corresponding to UPTG are described. Recombinant UPTG was labelled after incubation with UDP-[ 14 C]-Glc and Mn 2+ , indicating that it was enzymatically active. It was determined that purified as well as recombinant UPTG can be reversibly glycosylated by UDP-Glc, UDP-Xyl or UDP-Gal. RNA hybridization studies and western blot analysis indicate that UPTG mRNA and protein are expressed in all potato tissues. Databank searches revealed a high degree of identity between UPTG and several plant sequences that encode for proteins with apparent localization at the cytoplasmic face of the Golgi apparatus and at plasmodesmata. The biochemical properties of UPTG and the apparent lack of a signal peptide that could allow its entrance into plastids argue against the postulated role of UPTG in starch synthesis and point towards a possible role of the protein in the synthesis of cell wall polysaccharides.

Root-emitted volatile organic compounds: can they mediate belowground plant-plant interactions?

BackgroundAboveground, plants release volatile organic compounds (VOCs) that act as chemical signals between neighbouring plants. It is now well documented that VOCs emitted by the roots in the plant rhizosphere also play important ecological roles in the soil ecosystem, notably in plant defence because they are involved in interactions between plants, phytophagous pests and organisms of the third trophic level. The roles played by root-emitted VOCs in between- and within-plant signalling, however, are still poorly documented in the scientific literature.ScopeGiven that (1) plants release volatile cues mediating plant-plant interactions aboveground, (2) roots can detect the chemical signals originating from their neighbours, and (3) roots release VOCs involved in biotic interactions belowground, the aim of this paper is to discuss the roles of VOCs in between- and within-plant signalling belowground. We also highlight the technical challenges associated with the analysis of root-emitted VOCs and the design of experiments targeting volatile-mediated root-root interactions.ConclusionsWe conclude that root-root interactions mediated by volatile cues deserve more research attention and that both the analytical tools and methods developed to study the ecological roles played by VOCs in interplant signalling aboveground can be adapted to focus on the roles played by root-emitted VOCs in between- and within-plant signalling.

Identification of cytosolic Mg2+-dependent soluble inorganic pyrophosphatases in potato and phylogenetic analysis

Using polyclonal antibodies raised against a previously cloned potato Mg2+-dependent soluble inorganic pyrophosphatase (ppa1 gene) [8], a second gene, called ppa2, could be isolated. A single locus homologous to ppa2 was mapped on potato chromosomes, unlinked to the two loci identified for ppa1. From a phylogenetic and structural point of view, the PPA1 and PPA2 polypeptides are more closely related to prokaryotic than to eukaryotic Mg2+-dependent soluble inorganic pyrophosphatases (soluble PPases). Subcellular localization by immunogold electron microscopy, using sections from leaf parenchyma cells, showed that PPA1 and PPA2 are localized to the cytosol. Based on these observations, the likely phylogenetic origin and the physiological significance of the cytosolic soluble pyrophosphatases are discussed.

Genetic Diversity In The Lima Bean (Phaseolus Lunatus L.) As Revealed By Chloroplast Dna (Cpdna) Variations

Genetic diversity in the Lima bean (P. lunatus L.) was assessed bymeans of two chloroplast DNA probes. Based on data obtained from 152accessions including wild forms and landraces, the two separateMesoamerican and Andean groups were confirmed and a transition poolof genetic diversity was observed in the two botanical formsconsistent with their distribution range. Three primary centres ofgenetic diversity and one secondary diversification spot are proposedfor the wild Lima bean whereas only two domestication sites areunderlined for the landraces. The importance of human intervention inwidening the distribution range and the genetic diversity inlandraces is discussed.

Characterization of volatile organic compounds emitted by Barley (Hordeum vulgare L.) roots and their attractiveness to wireworms

Root volatile organic compounds (VOCs), their chemistry and ecological functions have garnered less attention than aboveground emitted plant VOCs. We report here on the identification of VOCs emitted by barley roots (Hordeum vulgare L.). Twenty nine VOCs were identified from isolated 21-d-old roots. The detection was dependent on the medium used for root cultivation. We identified 24 VOCs from 7-d-old roots when plants were cultivated on sterile Hoagland gelified medium, 33 when grown on sterile vermiculite, and 34 on non-sterile vermiculite. The major VOCs were fatty acid derived compounds, including hexanal, methyl hexanoate, (E)-hex-2-enal, 2-pentylfuran, pentan-1-ol, (Z)-2-(pentenyl)-furan, (Z)-pent-2-en-1-ol, hexan-1-ol, (Z)-hex-3-en-1-ol, (E)-hex-2-en-1-ol, oct-1-en-3-ol, 2-ethylhexan-1-ol (likely a contaminant), (E)-non-2-enal, octan-1-ol, (2E,6Z)-nona-2,6-dienal, methyl (E)-non-2-enoate, nonan-1-ol, (Z)-non-3-en-1-ol, (E)-non-2-en-1-ol, nona-3,6-dien-1-ol, and nona-2,6-dien-1-ol. In an olfactometer assay, wireworms (larvae of Agriotes sordidus Illiger, Coleoptera: Elateridae) were attracted to cues emanating from barley seedlings. We discuss the role of individual root volatiles or a blend of the root volatiles detected here and their interaction with CO2 for wireworm attraction.

Isolation and sequence analysis of a cDNA clone encoding a subunit of the ADP-glucose pyrophosphorylase of potato tuber amyloplasts

ADP-glucose pyrophosphorylase (ATP: a-glucose-l-P adenylyl-transferase, EC 2.2.7.27) catalyses the activation of glucosel-P into ADP-glucose, a rate-limiting step in starch biosynthesis [8, 13, 14]. The potato tuber enzyme is composed of two distinct subunits [ 10] and is located in the amyloplast [6]. This subunit composition and the plastid location characterize all plant ADP-glucose pyrophosphorylases studied so far, including isoforms of both leaf and storage tissues. In chloroplasts, the enzyme activity oscillates in response to the fluctuating levels of aUosteric effectors. To a large extent, the 3-P-glycerate/orthophosphate ratio (activator/inhibitor) regulates the transient production of starch in leaf tissues, by controlling the ADP-glucose pyrophosphorylase activity [13, 14]. Whether this aUosteric regulation (involving photosynthetic metabolites) operates in seeds and tubers is questionable. In this case, the onset of starch storage could involve de novo enzyme synthesis and such is apparently the case in developing wheat endosperms [ 16]. Very little is known on the expression of the corresponding genes during development, cDNA clones have been isolated in cereals, from rice endosperms [7, 1], maize endosperms [3, 15] and wheat leaves and endosperms [ 11 ], but not yet from storage organs of dicotyledonous species. A presumed 3-P-glycerate binding site of the spinach leaf enzyme has been identified and sequenced [9]. A 1 I-amino-acid consensus is observed between this site and the deduced amino acid sequence of a rice endosperm cDNA [7]. In order to isolate cDNA clones coding for the potato tuber ADP-glucose pyrophosphorylase, we postulated that the same consensus were present in the tuber enzyme. Indeed, the potato tuber enzyme has been extensively purified [18, 10] and shown to be activated in vitro by 3-P-glycerate [ 18]. A 32-mer oligonucleotide was synthesized, corresponding to the 11 conserved amino acids and using the codon sequence of a rice cDNA [ 1 ]. In a northern analysis, the oligonucleotide specifically hybridized with growing tuber RNAs and with wheat endosperm RNAs, with estimated sizes of 1800 nt. The latter observation is in good agreement with Krishnan et al. [7] who showed that the rice endosperm cDNA hybridizes with wheat endosperm RNAs of similar size. Hence, the oligonucleotide probe was used for the screening of a cDNA library, constructed from growing tuber poly(A) + RNA (cultivar D6sirre). The cDNAs were synthesized according to Gubler and Hoffman [4] and cloned into 2gtll , with LE392 as the host strain. The homologous cDNAs were subcloned into pBluescript KS( + ) (Stratagene). After ExonucleaselII deletion [5], the largest insert was sequenced by the dideoxy chain termination method [17] using T7 DNA polymerase. This cDNA (clone pAPT1) is 1627 bp in length, with a 1329bp coding region (Fig. 1). The nucleotide and