Cobalamin inactivation induces formyltetrahydrofolate synthetase

Loss of cobalamin function produces profound changes in the metabolism of formate. There is impaired synthesis of formyltetrahydropteroylglutamate synthetase (CHO-H4PteGlu), accumulation of endogenous formate and impaired utilization of [14C]formate. There are contradictory reports on the effect of cobalamin inactivation on CHO-H4PteGlu synthetase. This study confirms a significant increase in synthetase activity following cobalamin inactivation.     

Phylogeography and climatic niche evolution in live oaks (Quercus series Virentes) from the tropics to the temperate zone

Aim We investigated the phylogeography, geographical variation in leaf morphology, freezing tolerance and climatic niches of two widespread evergreen sister oak species (Quercus) in the series Virentes. Location South‐eastern USA, Mexico and Central America. Methods Nuclear microsatellites and non‐recombining nuclear and chloroplast DNA sequences were obtained from trees throughout the range of two sister lineages of live oaks, represented by Quercus virginiana in the temperate zone and Q. oleoides in the tropics. Divergence times were estimated for the two major geographical and genetic breaks. Differentiation in leaf morphology, analysed from field specimens, was compared with the molecular data. Freezing sensitivities of Q. virginiana and Q. oleoides populations were assessed in common garden experiments. Results The geographical break between Q. virginiana and Q. oleoides was associated with strong genetic differentiation of possible early Pleistocene origin and with differentiation in freezing sensitivity, climatic envelopes and leaf morphology. A second important geographical and genetic break within Q. oleoides between Costa Rica and the rest of Central America showed a mid‐Pleistocene divergence time and no differentiation in leaf morphology. Population genetic differentiation was greater but genetic diversity was lower within the temperate Q. virginiana than within the tropical Q. oleoides, and genetic breaks largely corresponded to breaks in leaf morphology. Main conclusions Two major breaks, one between Mexico and the USA at the boundary of the two species, and a more recent one within Q. oleoides between Honduras and Costa Rica, implicate climatic changes as potential causes. The latter break may be associated with the formation of the Cordillera de Guanacaste, which was followed by seasonal changes in precipitation. In the former case, an ‘out of the tropics’ scenario is hypothesized, in which the acquisition of freezing tolerance in Q. virginiana permitted colonization of and expansion in the temperate zone, while differences in climatic tolerances between the species limited secondary contact. More pronounced Pleistocene changes in climate and sea level in the south‐eastern USA relative to coastal Mexico and Central America may explain the greater population differentiation within temperate Q. virginiana and greater genetic diversity in tropical Q. oleoides. These patterns are predicted to hold for other taxa that span temperate and tropical zones of North and Central America.     

Colonization of wheat roots from seed‐applied spores of Idriella (Microdochium) bolleyi: A biocontrol agent of take‐all

Wheat seedlings were grown in containers of perlite in a glasshouse, and spores of Idriella bolleyi were applied either to the seeds in alginate gel or to the perlite as aqueous suspensions. Growth and sporulation of the fungus on seeds and roots were assessed by plating methods and by retrieval of spores from water that drained from the plant containers. Idriella bolleyi sporulated heavily on seeds for up to 3 weeks when applied to them in alginate gel, andmost of the root system was infected from newly formed spores that were carried in percolating water. Removal of the inoculated seeds from seedlings at 7 days reduced the degree of root infection and temporarily reduced the number of spores in drainage water; however, spore numbers increased to control levels (seeds attached) by 21 days, indicating subsequent sporulation on the roots. When spores were applied to perlite containing young (0–3 days) seedlings I. bolleyi colonized the seeds, sporulated heavily on them and extensively colonized the roots. However, it established poorly on seeds and roots if added to the perlite when seedlings were 11 days or older. The results suggest that early growth on seeds is necessary for establishment of a high population of I. bolleyi, and that cycles of sporulation on seeds and then roots contribute to colonization of the rhizosphere. The features associated with the rhizosphere competence of I. bolleyi are compared with those for systemic colonization of the xylem by vascular wilt fungi, and suggest a new approach to the selection of root‐colonizing biocontrol agents.     

β-Fructofuranosidases from roots of dandelion (Taraxacum officinale Weber)

1. Three beta-fructofuranosidases were separated by chromatography on a DEAE-cellulose column from the soluble protein extracted from dandelion (Taraxacum officinale Weber) roots. 2. One enzyme, which acted on sucrose, was characterized as an invertase, with a K(m) of 2.00x10(-2)m and pH optimum of 7.5. 3. The other two enzymes are hydrolases (A and B), which act on the inulin series of oligosaccharides [general formula glucose-fructose-(fructose)(n)]. They both have a pH optimum of 4.0 and K(m) of 1.54x10(-2)m but differ in their chromatographic behaviour on DEAE-cellulose. Neither of the hydrolases is inhibited by sucrose. 4. The physiological role of these three hydrolytic enzymes is discussed.     

MEK kinase 3 directly activates MKK6 and MKK7, specific activators of the p38 and c-Jun NH2-terminal kinases.

Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase kinase kinase 3 (MEKK3) activates the c-Jun NH2-terminal kinase (JNK) pathway, although no substrates for MEKK3 have been identified. We have examined the regulation by MEKK3 of MAPK kinase 7 (MKK7) and MKK6, two novel MAPK kinases specific for JNK and p38, respectively. Coexpression of MKK7 with MEKK3 in COS-7 cells enhanced MKK7 autophosphorylation and its ability to activate recombinant JNK1 in vitro. MKK6 autophosphorylation and in vitro activation of p38alpha were also observed following coexpression of MKK6 with MEKK3. MEKK2, a closely related homologue of MEKK3, also activated MKK7 and MKK6 in COS-7 cells. Importantly, immunoprecipitates of either MEKK3 or MEKK2 directly activated recombinant MKK7 and MKK6 in vitro. These data identify MEKK3 as a MAPK kinase kinase specific for MKK7 and MKK6 in the JNK and p38 pathways. We have also examined whether MEKK3 or MEKK2 activates p38 in intact cells using MAPK-activated protein kinase-2 (MAPKAPK2) as an affinity ligand and substrate. Anisomycin, sorbitol, or the expression of MEKK3 in HEK293 cells enhanced MAPKAPK2 phosphorylation, whereas MEKK2 was less effective. Furthermore, MAPKAPK2 phosphorylation induced by MEKK3 or cellular stress was abolished by the p38 inhibitor SB-203580, suggesting that MEKK3 is coupled to p38 activation in intact cells.