Expression and roles of NpABC1 : a Nicotiana plumbaginifolia ABC transporter involved in the plant-pathogen response

ATP-binding cassette (ABC) transporters represent one of the largest gene families in prokaryotes and eukaryotes, and transport a variety of substrates in organelles or to the intra- or extracellular space. They fulfill different physiological roles, such as import of small nutrients, drug resistance, transport of cytosolic peptides for antigen presentation, or ion channel regulation. In plants, the ABC protein family is particularly large, with 131 members in Arabidopsis, only a minority of which has been characterized at the functional level. Numerous ABC proteins belonging to the multidrug resistance-associated protein (MRP) cluster were characterized and shown to be involved in sequestering secondary metabolites in the vacuole. Much less is known concerning the members of the pleiotropic drug resistance (PDR) cluster. Among them, the Nicotiana plumbaginifolia ABC1 (NpABC1) has been localized to the plasma membrane and is thought to transport diterpenes, such as sclareol, involved in the plant defense. We show here that the NpABC1 gene is expressed in the leaf hairs involved in the secretion of defense molecules, but that it is also expressed in the whole leaf following insect or bacteria attack. Blocking NpABC1 expression through RNA interference rendered transgenic plants more susceptible to bacterial infection and sclareol toxicity. These data indicate that NpABC1 is involved in the pathogen response, possibly via sclareol and other antimicrobial related terpene secretion, and define a new role for the ABC transporter family. Furthermore, NpABC1 has been localized in the petal epidermis cells involved in volatile production. The highest expression was found when the flower is ready to function as a pollen donor and receiver, a developmental period corresponding to the highest emission of pollinator attracting molecules. This suggests the involvement of the ABC protein in the pollinator attraction via volatile emission. The detection of NpABC1 expression in the N. plumbaginifolia root remains to be investigated since preventing its expression through RNA interference resulted in rotting of the root tissues. These data show that NpABC1 is expressed in different organs and is involved in various physiological roles linked to the transport of secondary metabolites.Doctorat en sciences agronomiques et ingénierie biologique (AGRO 3)--UCL, 200

NpPDR1, a pleiotropic drug resistance-type ATP-binding cassette transporter from Nicotiana plumbaginifolia, plays a major role in plant pathogen defense.

Nicotiana plumbaginifolia NpPDR1, a plasma membrane pleiotropic drug resistance-type ATP-binding cassette transporter formerly named NpABC1, has been suggested to transport the diterpene sclareol, an antifungal compound. However, direct evidence for a role of pleiotropic drug resistance transporters in the plant defense is still lacking. In situ immunolocalization and histochemical analysis using the gusA reporter gene showed that NpPDR1 was constitutively expressed in the whole root, in the leaf glandular trichomes, and in the flower petals. However, NpPDR1 expression was induced in the whole leaf following infection with the fungus Botrytis cinerea, and the bacteria Pseudomonas syringae pv tabaci, Pseudomonas fluorescens, and Pseudomonas marginalis pv marginalis, which do not induce a hypersensitive response in N. plumbaginifolia, whereas a weaker response was observed using P. syringae pv syringae, which does induce a hypersensitive response. Induced NpPDR1 expression was more associated with the jasmonic acid than the salicylic acid signaling pathway. These data suggest that NpPDR1 is involved in both constitutive and jasmonic acid-dependent induced defense. Transgenic plants in which NpPDR1 expression was prevented by RNA interference showed increased sensitivity to sclareol and reduced resistance to B. cinerea. These data show that NpPDR1 is involved in pathogen resistance and thus demonstrate a new role for the ATP-binding cassette transporter family

A Plant Plasma Membrane ATP Binding Cassette–Type Transporter Is Involved in Antifungal Terpenoid Secretion

ATP binding cassette (ABC) transporters, which are found in all species, are known mainly for their ability to confer drug resistance. To date, most of the ABC transporters characterized in plants have been localized in the vacuolar membrane and are considered to be involved in the intracellular sequestration of cytotoxins. Working on the assumption that certain ABC transporters might be involved in defense metabolite secretion and their expression might be regulated by the concentration of these metabolites, we treated a Nicotiana plumbaginifolia cell culture with sclareolide, a close analog of sclareol, an antifungal diterpene produced at the leaf surface of Nicotiana spp; this resulted in the appearance of a 160-kD plasma membrane protein, which was partially sequenced. The corresponding cDNA (NpABC1) was cloned and shown to encode an ABC transporter. In vitro and in situ immunodetection showed NpABC1 to be localized in the plasma membrane. Under normal conditions, expression was found in the leaf epidermis. In cell culture and in leaf tissues, NpABC1 expression was strongly enhanced by sclareolide and sclareol. In parallel with NpABC1 induction, cells acquired the ability to excrete a labeled synthetic sclareolide derivative. These data suggest that NpABC1 is involved in the secretion of a secondary metabolite that plays a role in plant defense

Involvement of Pyruvate Oxidase Activity and Acetate Production in the Survival of Lactobacillus plantarum during the Stationary Phase of Aerobic Growth

In addition to the previously characterized pyruvate oxidase PoxB, the Lactobacillus plantarum genome encodes four predicted pyruvate oxidases (PoxC, PoxD, PoxE, and PoxF). Each pyruvate oxidase gene was individually inactivated, and only the knockout of poxF resulted in a decrease in pyruvate oxidase activity under the tested conditions. We show here that L. plantarum has two major pyruvate oxidases: PoxB and PoxF. Both are involved in lactate-to-acetate conversion in the early stationary phase of aerobic growth and are regulated by carbon catabolite repression. A strain devoid of pyruvate oxidase activity was constructed by knocking out the poxB and poxF genes. In this mutant, acetate production was strongly affected, with lactate remaining the major end product of either glucose or maltose fermentation. Notably, survival during the stationary phase appeared to be dramatically improved in the poxB poxF double mutant