Pathogenesis-related proteins of class 10 (PR-10) are a family of plant proteins with the same fold characterized by a large hydrophobic cavity that allows them to bind various ligands, such as phytohormones. A subfamily with only ~20% sequence identity but with a conserved canonical PR-10 fold have previously been recognized as Cytokinin-Specific Binding Proteins (CSBPs), although structurally the binding mode of trans-zeatin (a cytokinin phytohormone) was found to be quite diversified. Here, it is shown that two CSBP orthologues from Medicago truncatula and Vigna radiata bind gibberellic acid (GA3), which is an entirely different phytohormone, in a conserved and highly specific manner. In both cases a single GA3 molecule is found in the internal cavity of the protein. The structural data derived from high-resolution crystal structures are corroborated by isothermal titration calorimetry (ITC), which reveals a much stronger interaction with GA3 than with trans-zeatin and pH dependence of the binding profile. As a conclusion, it is postulated that the CSBP subfamily of plant PR-10 proteins should be more properly linked with general phytohormone-binding properties and termed phytohormone-binding proteins (PhBP).

No abstract

The cellulolytic activity (exoglucanase, endoglucanase and b-glucosidase) of Ophiostoma ulmi (four isolates), O. novo-ulmi (19 isolates) and Ôfast-waxyÕ (five isolates) was determined in growth media containing carboxymethylcellulose (CMC) and cellulose powder. Differences in enzyme activities were observed among isolates, irrespective of the species and substrate used. Inoculation experiments on Ulmus minor with randomly selected isolates of O. ulmi (two isolates), O. novo-ulmi (five isolates) and Ôfast-waxyÕ (two isolates) were also performed. Disease was assessed as the percentage of leaves showing yellowing and browning. Ophiostoma novo-ulmi and Ôfast-waxyÕ isolates exhibited a great variability in their capacities to cause the disease. In the presence of CMC, a significant correlation between the activity of exoglucanase and b-glucosidase in vitro and virulence was found.

No abstract

The effect of ecomycorrhizal fungi (<i>Hebelon crustuliniforme</i>(Bull.: Fr.) Quél. 5392 and <i> Pisolithus tinctorius</i> (Pers.) Coker et Couch 5335) and bacteria (<i>Bacillus polymyxa</i> and <i>Azospirillum brasilense</i>). associated with mycorrhizas on the growth of pine seedligs was investigated. In addition the influence of bacteria on fungal biomass production and the relationship between ectomycorrhizal fungi and fungi pathogenic to root of pine seedlings were determined. In general, the shoot/root ratio was higher in plants inoculated with <i>Hebeloma crustuliniforme</i> and bacteria than in the control seedlings (grown only under sterile conditions). In non-sterile substrate the root/shoot ratio of the mycorrhizal seedlings was lower as compared to the control. Similar phenomenon was noted in plants inoculated with the mycorrhizal fungus <i>Pisolithus tinetorius</i>. The bacteria used as well as the time of introduction of these organisms into the cultures of mycorrhiza fungi affected the production of fungal biomass. <i>Hebeloma crustuliniforme</i> and <i>Pisolithus tinctorius</i> inhibited the growth of <i>Rizoctonia solani</i> and <i>Fusarium oxysporum</i> fungi pathogenic to pine seedlings.