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

Arbuscular 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.

The Arabidopsis nitrate transporter NPF7.3/NRT1.5 is involved in lateral root development under potassium deprivation.

Plants have evolved a large array of transporters and channels that are responsible for uptake, source-to-sink distribution, homeostasis and signaling of nitrate (NO3(-)), which is for most plants the primary nitrogen source and a growth-limiting macronutrient. To optimize NO3(-) uptake in response to changing NO3(-) concentrations in the soil, plants are able to modify their root architecture. Potassium is another macronutrient that influences the root architecture. We recently demonstrated that the Arabidopsis NO3(-) transporter NPF7.3/NRT1.5, which drives root-to-shoot transport of NO3(-), is also involved in root-to-shoot translocation of K(+) under low NO3(-) nutrition. Here, we show that K(+) shortage, but not limiting NO3(-) supply, causes in nrt1.5 mutant plants an altered root architecture with conspicuously reduced lateral root density. Since lateral root development is influenced by auxin, we discuss a possible involvement of NPF7.3/NRT1.5 in auxin homeostasis in roots under K(+) deprivation.

Nitrate-Dependent Control of Shoot K Homeostasis by the Nitrate Transporter1/Peptide Transporter Family Member NPF7.3/NRT1.5 and the Stelar K+ Outward Rectifier SKOR in Arabidopsis.

Root-to-shoot translocation and shoot homeostasis of potassium (K) determine nutrient balance, growth, and stress tolerance of vascular plants. To maintain the cation-anion balance, xylem loading of K(+) in the roots relies on the concomitant loading of counteranions, like nitrate (NO3 (-)). However, the coregulation of these loading steps is unclear. Here, we show that the bidirectional, low-affinity Nitrate Transporter1 (NRT1)/Peptide Transporter (PTR) family member NPF7.3/NRT1.5 is important for the NO3 (-)-dependent K(+) translocation in Arabidopsis (Arabidopsis thaliana). Lack of NPF7.3/NRT1.5 resulted in K deficiency in shoots under low NO3 (-) nutrition, whereas the root elemental composition was unchanged. Gene expression data corroborated K deficiency in the nrt1.5-5 shoot, whereas the root responded with a differential expression of genes involved in cation-anion balance. A grafting experiment confirmed that the presence of NPF7.3/NRT1.5 in the root is a prerequisite for proper root-to-shoot translocation of K(+) under low NO3 (-) supply. Because the depolarization-activated Stelar K(+) Outward Rectifier (SKOR) has previously been described as a major contributor for root-to-shoot translocation of K(+) in Arabidopsis, we addressed the hypothesis that NPF7.3/NRT1.5-mediated NO3 (-) translocation might affect xylem loading and root-to-shoot K(+) translocation through SKOR. Indeed, growth of nrt1.5-5 and skor-2 single and double mutants under different K/NO3 (-) regimes revealed that both proteins contribute to K(+) translocation from root to shoot. SKOR activity dominates under high NO3 (-) and low K(+) supply, whereas NPF7.3/NRT1.5 is required under low NO3 (-) availability. This study unravels nutritional conditions as a critical factor for the joint activity of SKOR and NPF7.3/NRT1.5 for shoot K homeostasis.

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.