Egg Laying of Cabbage White Butterfly (Pieris brassicae) on Arabidopsis thaliana Affects Subsequent Performance of the Larvae

Plant resistance to the feeding by herbivorous insects has recently been found to be positively or negatively influenced by prior egg deposition. Here we show how crucial it is to conduct experiments on plant responses to herbivory under conditions that simulate natural insect behaviour. We used a well- studied plant – herbivore system, Arabidopsis thaliana and the cabbage white butterfly Pieris brassicae, testing the effects of naturally laid eggs (rather than egg extracts) and allowing larvae to feed gregariously as they do naturally (rather than placing single larvae on plants). Under natural conditions, newly hatched larvae start feeding on their egg shells before they consume leaf tissue, but access to egg shells had no effect on subsequent larval performance in our experiments. However, young larvae feeding gregariously on leaves previously laden with eggs caused less feeding damage, gained less weight during the first 2 days, and suffered twice as high a mortality until pupation compared to larvae feeding on plants that had never had eggs. The concentration of the major anti-herbivore defences of A. thaliana, the glucosinolates, was not significantly increased by oviposition, but the amount of the most abundant member of this class, 4-methylsulfinylbutyl glucosinolate was 1.8-fold lower in larval-damaged leaves with prior egg deposition compared to damaged leaves that had never had eggs. There were also few significant changes in the transcript levels of glucosinolate metabolic genes, except that egg deposition suppressed the feeding-induced up-regulation of FMOGS-OX2, a gene encoding a flavin monooxygenase involved in the last step of 4-methylsulfinylbutyl glucosinolate biosynthesis. Hence, our study demonstrates that oviposition does increase A. thaliana resistance to feeding by subsequently hatching larvae, but this cannot be attributed simply to changes in glucosinolate content

The nitrate transporter AtNRT1.5/AtNPF7.3 - a key regulator in plant potassium homeostasis

Kalium (K) und Stickstoff (N) in Form von Nitrat (NO3-) oder Ammonium (NH4+) sind die zwei quantitativ am häufigsten von der Pflanze aufgenommenen Makroelemente. Ihre Transport- und Signalwege stehen dabei in enger Wechselwirkung. Die Mechanismen, die diesem dy-mischen Netzwerk zugrunde liegen, sind bisher allerdings wenig erforscht. Die Ergebnisse dieser Arbeit dokumentieren, dass ein Mitglied der Arabidopsis Nitrate Trans-porter1 (NRT1)/Peptide Transporter (PTR) Family (NPF) in diese komplexen Transportpro- zesse involviert ist: der bidirektionale und niedrig-affine Nitrattransporter NRT1.5/NPF7.3. Phänotypische und physiologische Untersuchungen von nrt1.5 Knockout Mutanten zeigten, dass das NRT1.5 Protein an der NO3--abhängigen Kaliumtranslokation zwischen Wurzel und Spross beteiligt ist. Unter niedriger Nitratverfügbarkeit entwickeln nrt1.5 Pflanzen einen starken Kaliummangel im Spross, der mit den klassischen sichtbaren K+-Mangelsymptomen wie der Bildung von Chlorosen an älteren Blättern einhergeht. Die Induktion von K+-Mangel- assoziierten Genen und die Erhöhung der Jasmonsäure- und Glucosinolatkonzen¬trationen in den nrt1.5 Rosettenblättern bestätigen zudem die Initiierung einer Kaliummangel-bedingten Signalkaskade im nrt1.5 Spross. Homo- und heteroplastische Pfropfungen zwischen Col-0 und nrt1.5-5 Pflanzen offenbarten, dass die Beeinträchtigung des Wurzel-Spross Kalium-transfers ausschließlich auf den Verlust der NRT1.5 Wurzelaktivität zurückzuführen ist. Die mit Hilfe von Promotor-GUS Studien aufgezeigten NRT1.5 Expressionen indizieren jedoch weitere Proteinfunktionen in unterschiedlichen Wurzel- und Sprossgeweben. Während die Elementanalysen in den Wurzel- und Sprossproben der gepfropften Pflanzen keine Hinweise für eine die Nährstoffhomöostase beeinflussende NRT1.5 Sprossaktivität liefern, führt die gezielte sprossspezifische NRT1.5 Überexpression in den nrt1.5 Mutanten zu einer toxischen Natriumanreicherung. Interessanterweise korrelieren die erhöhten Na+-Konzentrationen im Spross der NRT1.5 Überexpressionslinien mit einer hohen externen Nitratversorgung. Demzufolge moduliert das NRT1.5 Protein über seine Wurzelaktivität einerseits den pflanzlichen Kaliumhaushalt unter Nitratmangel und steuert andererseits über seine Sprossaktivität die Natriumhomöostase unter hoher Nitratverfügbarkeit. Die moleku-laren Grundlagen dieser diffizilen Zusammenhänge sind bislang noch nicht aufgeklärt. Die Identifizierung mehrerer NRT1.5 Interaktionspartner im heterologen Hefe-Split-Ubiquitin System deutet jedoch darauf hin, dass das Nitrattransportprotein über eine Protein-Protein Interaktion in die posttranslationale Regulation des Kaliumtransports involviert ist. Neben Interaktionen mit Kaliumtransport-assoziierten Proteinen wie SLAH1, SLAH3, CIPK9-CBL3 und VAMP722, wurden dabei auch Wechselwirkungen mit der für die Steuerung des Mem-branpotentials relevanten H+-ATPase AHA2 nachgewiesen.Potassium (K) and Nitrogen (N) in the form of nitrate (NO3−) or ammonium (NH4+) are the two most abundantly acquired macroelements by plants and their transport and signaling path¬ways interact in complex ways. However, the underlying mechanisms of these dynamic inter¬actions remain to be determined. Here, we show that one member of the Arabidopsis thaliana Transporter1 (NRT1)/Peptide Transporter (PTR) family is involved in these sophisticated transport processes: the bidirec-tional and low-affinity nitrate transporter NRT1.5/NPF7.3. Phenotypic und physiological characterization of nrt1.5 knockout mutants revealed that NRT1.5 activity is important for the NO3-- dependent K+ translocation between root and shoot. Under low NO3- nutrition, lack of NRT1.5 provokes a severe potassium deficit in shoot organs accompanied by typical K+ deficiency symptoms like chlorotic leaves. The shoot gene expression data and the higher concentrations of jasmonic acid and glucosinolates in nrt1.5 rosettes corroborate the initiation of the K deficiency signaling cascades in the nrt1.5 shoot. Although grafting experiments between Col-0 and nrt1.5 plants indicated that impairment of potassium translocation to the shoot is attributed exclusively to the absence of the NRT1.5 root activity, promoter GUS analysis demonstrated NRT1.5 expression signals in different shoot and root tissues suggesting further functions within the plant. Elemental analysis in root and shoot organs of grafted plants does not provide evidence for an involvement of NRT1.5 shoot activity in nutrient homeostasis. Notwithstanding, shoot specific overexpression of NRT1.5 in nrt1.5 knockout mutant plants results in higher shoot sodium concen¬trations. Interestingly, shoot sodium accumulation of NRT1.5 overexpression lines correlates with high external NO3- supply. These data suggest that NRT1.5 modulates plant K+ homeostasis under nitrate starvation via its root activity on the one hand and Na+ homeostasis under ample nitrate supply via its shoot activity on the other hand. The molecular basis of these intricate interrelations is still un¬known. But the identification of several NRT1.5 interacting proteins using the heterologous yeast split-ubiquitin system denotes a participation of the nitrate transporter NRT1.5 in the post-translational regulation of potassium transport via protein-protein interactions. In addition to K+ transport associated proteins like SLAH1, SLAH3, CIPK9-CBL3 and VAMP722 the split-ubiquitin screen also uncovered an interaction with the H+-ATPase AHA2 pointing to an involvement of NRT1.5 in the modulation of the membrane potential or the membrane protonmotive force

Identification of arbuscular mycorrhiza-inducible Nitrate Transporter 1/Peptide Transporter Family (NPF) genes in rice

SPE IPM UBInternational audienceArbuscular mycorrhizal fungi (AMF) colonize up to 90% of all land plants and facilitate the acquisition of mineral nutrients by their hosts. Inorganic orthophosphate (Pi) and nitrogen (N) are the major nutrients transferred from the fungi to plants. While plant Pi transporters involved in nutrient transfer at the plant-fungal interface have been well studied, the plant N transporters participating in this process are largely unknown except for some ammonium transporters (AMT) specifically assigned to arbuscule-colonized cortical cells. In plants, many nitrate transporter 1/peptide transporter family (NPF) members are involved in the translocation of nitrogenous compounds including nitrate, amino acids, peptides and plant hormones. Whether NPF members respond to AMF colonization, however, is not yet known. Here, we investigated the transcriptional regulation of 82 rice (Oryza sativa) NPF genes in response to colonization by the AMF Rhizophagus irregularis in roots of plants grown under five different nutrition regimes. Expression of the four OsNPF genes NPF2.2/PTR2, NPF1.3, NPF6.4 and NPF4.12 was strongly induced in mycorrhizal roots and depended on the composition of the fertilizer solution, nominating them as interesting candidates for nutrient signaling and exchange processes at the plant-fungal interface

Effects of prior egg deposition and egg shell consumption (a typical behaviour of neonate larvae) on larval performance (means ± SE) of <i>Pieris brassicae</i> on <i>Arabidopsis thaliana</i> Col-0 plants¹ (for statistics, see Table 2).

1<p>Batches of 40 freshly hatched larvae either fed upon a plant with prior <i>P. brassicae</i> egg deposition (Egg) or without any eggs (Control) until they were 4 days old; thereafter, batches of 10 larvae where transferred to fresh, undamaged egg-free plants, where they completed their development until pupation. ² Larvae were allowed to feed upon their egg shells. ³ Larvae were prevented from feeding upon their egg shells during the first 2 days after hatching. ⁴ Number of batches of larvae (1 batch per plant; <i>N</i> = 8 for freshly hatched larvae; <i>N</i>  =  initially 4 for elder larvae).</p

Expression ratios of <i>FMO_GS-OX2</i> in leaves subjected to different oviposition and feeding treatments.

<p>Values are means ± standard errors of wild-type <i>Arabidopsis thaliana</i> plants (Col-0). C: untreated control leaves (<i>N</i> = 8); E: leaves on which eggs were laid and left for 5 days (<i>N</i> = 8); E+F: leaves on which eggs were laid and caterpillars hatched and fed for 2 days (<i>N</i> = 7); F: leaves that never had eggs but were fed on for 2 days (<i>N</i> = 7). Data were normalised to the amplification of ubiquitin, calibrated against the value of the control, and statistically evaluated by analyses of variance (ANOVA). Different letters above the columns indicate significant differences by means of Fisher's LSD test for <i>post hoc</i> comparisons (<i>P</i><0.05).</p