Auxin and nitric oxide control indeterminate nodule formation

<p>Abstract</p> <p>Background</p> <p>Rhizobia symbionts elicit root nodule formation in leguminous plants. Nodule development requires local accumulation of auxin. Both plants and rhizobia synthesise auxin. We have addressed the effects of bacterial auxin (IAA) on nodulation by using <it>Sinorhizobium meliloti </it>and <it>Rhizobium leguminosarum </it>bacteria genetically engineered for increased auxin synthesis.</p> <p>Results</p> <p>IAA-overproducing <it>S. meliloti </it>increased nodulation in <it>Medicago </it>species, whilst the increased auxin synthesis of <it>R. leguminosarum </it>had no effect on nodulation in <it>Phaseolus vulgaris</it>, a legume bearing determinate nodules. Indeterminate legumes (<it>Medicago </it>species) bearing IAA-overproducing nodules showed an enhanced lateral root development, a process known to be regulated by both IAA and nitric oxide (NO). Higher NO levels were detected in indeterminate nodules of <it>Medicago </it>plants formed by the IAA-overproducing rhizobia. The specific NO scavenger cPTIO markedly reduced nodulation induced by wild type and IAA-overproducing strains.</p> <p>Conclusion</p> <p>The data hereby presented demonstrate that auxin synthesised by rhizobia and nitric oxide positively affect indeterminate nodule formation and, together with the observation of increased expression of an auxin efflux carrier in roots bearing nodules with higher IAA and NO content, support a model of nodule formation that involves auxin transport regulation and NO synthesis.</p

Plants expressing murine pro-apoptotic protein Bid do not have enhanced PCD

The purpose of this study was to explore whether plant programmed cell death (PCD) cascade can sense the presence of the animal-only BH3 protein Bid, a BCL-2 family protein known to play a regulatory role in the signaling cascade of animal apoptosis

Calcium binding to the photosystem II subunit CP29.

We have identified a Ca(2+)-binding site of the 29-kDa chlorophyll a/b-binding protein CP29, a light harvesting protein of photosystem II most likely involved in photoregulation. (45)Ca(2+) binding studies and dot blot analyses of CP29 demonstrate that CP29 is a Ca(2+)-binding protein. The primary sequence of CP29 does not exhibit an obvious Ca(2+)-binding site therefore we have used Yb(3+) replacement to analyze this site. Near-infrared Yb(3+) vibronic side band fluorescence spectroscopy (Roselli, C., Boussac, A., and Mattioli, T. A. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 12897-12901) of Yb(3+)-reconstituted CP29 indicated a single population of Yb(3+)-binding sites rich in carboxylic acids, characteristic of Ca(2+)-binding sites. A structural model of CP29 presents two purported extra-membranar loops which are relatively rich in carboxylic acids, one on the stromae side and one on the lumenal side. The loop on the lumenal side is adjacent to glutamic acid 166 in helix C of CP29, which is known to be the binding site for dicyclohexylcarbodiimide (Pesaresi, P., Sandonà, D., Giuffra, E. , and Bassi, R. (1997) FEBS Lett. 402, 151-156). Dicyclohexylcarbodiimide binding prevented Ca(2+) binding, therefore we propose that the Ca(2+) in CP29 is bound in the domain including the lumenal loop between helices B and C

Analysis of the lipid binding properties of mutant murine Bid proteins

Bid is a BH3-only member of the Bcl-2 family that regulates cell death at the level of mitochondrial membranes. It is generally assumed that the full length Bid protein becomes activated after a proteolytic cleavage catalized by apical caspases, like caspase 8. The cleaved protein then re-locates to mitochondria and promotes membrane permeabilization, presumably by interaction with mitochondrial lipids and other Bcl-2 proteins that facilitate the release of apoptogenic proteins like cytochrome c. The un-cleaved Bid also has proapoptotic potential when ectopically expressed in cells or in vitro. It has been demonstrated that full length Bid can insert specific lysolipids into the membrane surface and this lipid transfer activity participates to the release of apoptogenic factors from mitochondria. The binding properties of Bid are still unknown. In this work we will present new full length Bid mutants that possess altered lipid binding properties and proapoptotic activities in vitro. We have analysed the binding properties of Bid mutants to LPC species and MCL (or LPG) in order to investigate the protein dual specificity for the diverse lysolipids

Lipid exchange in mitochondrial cytochrome c release: pro-apoptotic effect of maize lipid transfer protein

Membrane lipids and protein-lipid interactions are attracting increasing interest in the field of cell death and apoptosis. Some pro-apoptotic proteins, like Bid, appear to have an intrinsic capacity of binding and exchange lipids but it is still unclear whether this function could be relevant for apoptotic signalling cascade. We have studied the ability of a plant lipid transfer protein, not related to animal apoptotic cascade, to induce cytochrome c release from mammalian mitochondria. Non -specific lipid transfer proteins (nsLTPs) are ubiquitous plant proteins that have been shown to bind, in vitro, various amphiphilic molecules including lysolipids and glycolipids and to facilitate in vitro transfer of phospholipids between membranes. The results showed that, in the presence of specific lipid molecules (i.e. lysolipids), ns-LTP from maize is able to induce cytochrome c release from the intermembrane space of mouse liver mitochondria. These data are discussed with respect to the role played by lipids and lipid binding in apoptosis

Does MtN5 play a double role in root responses to symbiontic and pathogenic microorganisms?

MtN5, a new Lipid Transfer Protein, has been identified in nodulated roots of Medicago truncatula andpreliminarily classified as early nodulin, which is expressed in response to rhizobial symbiosis. Wehave shown that the recombinant MtN5 exerts antifungal and antimicrobial activity in vitro againstFusarium semitectum and Rhizobium leguminosarum, respectively. In vivo, the fungal infection leadsto the expression of MtN5 in the whole root apparatus of M. truncatula plants, whereas the inoculationwith rhizobia induces an early and nodule-specific expression of the protein, that is also maintained inmature nodules. These two different expression patterns suggest a putative double role for MtN5, whichcould be involved both in a general response mechanism against fungi and in sensing or controlling theinfection of the symbiont. This last hypothesis is supported by the observation that M.truncatula rootstransformed with an hairpin construct aiming to silence endogenous MtN5, are impaired in noduleformation respect to control roots. Therefore, MtN5 is hereby proposed as a novel, multifunctionalprotein taking part in the symbiotic process

Bioprospecting of Artemisia genus: from artemisinin to other potentially bioactive compounds

: Species from genus Artemisia are widely distributed throughout temperate regions of the northern hemisphere and many cultures have a long-standing traditional use of these plants as herbal remedies, liquors, cosmetics, spices, etc. Nowadays, the discovery of new plant-derived products to be used as food supplements or drugs has been pushed by the exploitation of bioprospection approaches. Often driven by the knowledge derived from the ethnobotanical use of plants, bioprospection explores the existing biodiversity through integration of modern omics techniques with targeted bioactivity assays. In this work we set up a bioprospection plan to investigate the phytochemical diversity and the potential bioactivity of five Artemisia species with recognized ethnobotanical tradition (A. absinthium, A. alba, A. annua, A. verlotiorum and A. vulgaris), growing wild in the natural areas of the Verona province. We characterized the specialized metabolomes of the species (including sesquiterpenoids from the artemisinin biosynthesis pathway) through an LC-MS based untargeted approach and, in order to identify potential bioactive metabolites, we correlated their composition with the in vitro antioxidant activity. We propose as potential bioactive compounds several isomers of caffeoyl and feruloyl quinic acid esters (e.g. dicaffeoylquinic acids, feruloylquinic acids and caffeoylferuloylquinic acids), which strongly characterize the most antioxidant species A. verlotiorum and A. annua. Morevoer, in this study we report for the first time the occurrence of sesquiterpenoids from the artemisinin biosynthesis pathway in the species A. alba