Zinc finger proteins act as transcriptional repressors of alkaloid biosynthesis genes in Catharanthus roseus

Plant science

A regulated deficit irrigation strategy for hedgerow olive orchards with high plant density

Background & Aims There is not a consensus on the best irrigation approach for super-high density (SHD) olive orchards. Our aim was to design and test a regulated deficit irrigation (RDI) strategy for a sustainable balance between water saving, tree vigour and oil production. Methods We tested our RDI strategy for 3 years in an ‘Arbequina’ orchard with 1,667 trees ha−1. Two levels of irrigation reduction were applied, 60RDI and 30RDI, scaled to replacing 60 % and 30 %, respectively, of the of irrigation needs (IN). We also had a full irrigation (FI) treatment as control, with IN totalling 4,701 m3 ha−1 Results The 30RDI treatment showed the best balance between water saving, tree vigour and oil production. With a yearly irrigation amount (IA) of 1,366 m3 ha−1, which meant 72 % water saving as compared to FI, the reduction in oil yield was 26 % only. Conclusions Our results, together with recent knowledge on the effect of water stress on fruit development, allowed us to suggest a potentially improved RDI strategy for which a total IA of ca. 2,100 m3 ha−1 was calculated. Both some management details and the benefits of this suggested RDI strategy are still to be tested

Plant lectins: the ties that bind in root symbiosis and plant defense

Lectins are a diverse group of carbohydrate-binding proteins that are found within and associated with organisms from all kingdoms of life. Several different classes of plant lectins serve a diverse array of functions. The most prominent of these include participation in plant defense against predators and pathogens and involvement in symbiotic interactions between host plants and symbiotic microbes, including mycorrhizal fungi and nitrogen-fixing rhizobia. Extensive biological, biochemical, and molecular studies have shed light on the functions of plant lectins, and a plethora of uncharacterized lectin genes are being revealed at the genomic scale, suggesting unexplored and novel diversity in plant lectin structure and function. Integration of the results from these different types of research is beginning to yield a more detailed understanding of the function of lectins in symbiosis, defense, and plant biology in general

Correlation between extracellular fibrils and attachment of Rhizobium leguminosarum to pea root hair tips.

As part of a project meant to characterize molecules involved in nodulation, a semiquantitative microscopic assay was developed for measuring attachment of Rhizobium leguminosarum cells to pea root hair tips, i.e., the site at which R. leguminosarum initiates nodulation. This form of attachment, designated as cap formation, was dependent on the incubation pH and growth phase, with optimal attachment at pH 7.5 and with bacteria in the early stationary phase of growth. Addition of glucose to the growth medium delayed the initiation of the stationary phase and cap formation, suggesting a correlation between cap formation and carbon limitation. Attachment of R. leguminosarum was not inhibited by pea lectin haptens which makes it unlikely that lectins are involved under the tested conditions. Moreover, heterologous fast-growing rhizobia adhered equally well to pea root hair tips. Since the attachment characteristics of a Sym plasmid-cured derivative were indistinguishable from those of the wild-type strain, the Sym plasmidborne nodulation genes are not necessary for attachment. Sodium chloride and various other salts abolished attachment when present during the attachment assay in final concentrations of 100 mM. R. leguminosarum produced extracellular fibrils. A positive correlation between the percentage of fibrillated cells and the ability of the bacteria to form caps and to adhere to glass and erythrocytes was observed under various conditions, suggesting that these fibrils play a role in attachment of the bacteria to pea root hair tips, to glass, and to erythrocytes

Roles of flagella, lipopolysaccharide, and a Ca2+-dependent cell surface protein in attachment of Rhizobium leguminosarum biovar viciae to pea root hair tips.

The relationship between Ca2+-dependent cell surface components of Rhizobium leguminosarum biovar viciae, motility, and ability to attach to pea root hair tips was investigated. In contrast to flagella and lipopolysaccharide, a small protein located on the cell surface was identified as the Ca2+-dependent adhesin

Rhicadhesin-mediated attachment and virulence of an Agrobacterium tumefaciens chvB mutant can be restored by growth in a highly osmotic medium.

Cyclic beta-1,2-glucan is considered to play a role in osmoadaptation of members of the family Rhizobiaceae in hypotonic media. Agrobacterium tumefaciens chvB mutants, lacking beta-1,2-glucan, exhibit a pleiotropic phenotype, including nonmotility, attachment deficiency, and avirulence. Here we report that by growth of chvB mutant cells in tryptone-yeast extract medium supplemented with 7 mM CaCl2 and 100 mM NaCl, the mutant cells become motile, attach to pea root hair tips, and are virulent on Kalanchoë leaves. Moreover, whereas chvB mutants grown in tryptone-yeast extract medium containing 7 mM CaCl2 do not produce active rhicadhesin, addition of 100 mM NaCl to this medium resulted in restoration of rhicadhesin activity. The presence of CaCl2 appeared to be required for attachment, virulence, and activity of rhicadhesin. The results support a role for cyclic beta-1,2-glucan in osmoadaptation and strengthen the notion that rhicadhesin is required for attachment and virulence of A. tumefaciens

Flocculence of Saccharomyces cerevisiae cells is induced by nutrient limitation, with cell surface hydrophobicity as a major determinant.

Initiation of flocculation ability of Saccharomyces cerevisiae MPY1 cells was observed at the moment the cells stop dividing because of nitrogen limitation. A shift in concentration of the limiting nutrient resulted in a corresponding shift in cell division and initiation of flocculence. Other limitations also led to initiation of flocculence, with magnesium limitation as the exception. Magnesium-limited S. cerevisiae cells did not flocculate at any stage of growth. Cell surface hydrophobicity was found to be strongly correlated with the ability of the yeast cells to flocculate. Hydrophobicity sharply increased at the end of the logarithmic growth phase, shortly before initiation of flocculation ability. Treatments of cells which resulted in a decrease in hydrophobicity also yielded a decrease in flocculation ability. Similarly, the presence of polycations increased both hydrophobicity and the ability to flocculate. Magnesium-limited cells were found to be strongly affected in cell surface hydrophobicity. A proteinaceous cell surface factor(s) was identified as a flocculin. This heat-stable component had a strong emulsifying activity, and appears to be involved in both cell surface hydrophobicity and in flocculation ability of the yeast cells