Cloning of a Cicer arietinum beta-galactosidase with pectin-degrading function

The cDNA clone (CanBGal-3) encoding a cell wall pectin-degrading beta-galactosidase (beta III-Gal) from Cicer arietinum L. cv. Castellana has been identified. The identification was carried out by comparing the deduced amino acid sequences of several isolated chickpea beta-galactosidase clones with the purified beta III-Gal protein sequence. The expression pattern of the gene corresponding to CanBGal-3 was in concordance with the fluctuations of the enzyme beta III-Gal in different seedling organs, being specific to elongating organs such as epicotyls and roots. Transformation of Solanum tuberosum plants with the chickpea CanBGal-3 clone indicated that the beta-galactosidase encoded by this clone is a pectin-degrading enzyme. The authors propose an important role for chickpea beta III-Gal in pectin degradation in cell walls of vegetative organs such as epicotyls and roots. The degradation of galactan carried out by this enzyme may determine structural changes and affect cell wall porosity. It is suggested that the increase in the size of cell wall pores could permit access of other cell wall-modifying enzymes to their substrate.     

Slit stimulation recruits Dock and Pak to the roundabout receptor and increases Rac activity to regulate axon repulsion at the CNS midline

Drosophila Roundabout (Robo) is the founding member of a conserved family of repulsive axon guidance receptors that respond to secreted Slit proteins. Here we present evidence that the SH3-SH2 adaptor protein Dreadlocks (Dock), the p21-activated serine-threonine kinase (Pak), and the Rac1/Rac2/Mtl small GTPases can function during Robo repulsion. Loss-of-function and genetic interaction experiments suggest that limiting the function of Dock, Pak, or Rac partially disrupts Robo repulsion. In addition, Dock can directly bind to Robo's cytoplasmic domain, and the association of Dock and Robo is enhanced by stimulation with Slit. Furthermore, Slit stimulation can recruit a complex of Dock and Pak to the Robo receptor and trigger an increase in Rac1 activity. These results provide a direct physical link between the Robo receptor and an important cytoskeletal regulatory protein complex and suggest that Rac can function in both attractive and repulsive axon guidance.     

Partial purification of cell wall α-galactosidases and α-arabinosidases from Cicer arietinum epicotyls. Relationship with cell wall autolytic processes

Two protein fractions with activity as α-galactosidase (EC 3.2.1.22) and α-arabinosidase (EC 3.2.1.55), respectively, were identified in the proteins of cell wall of Cicer arietinum L. cv. Castellana extracted with 3 M LiCl. These fractions were partially purified by gel filtration chromatography (Bio Gel P-150), increasing the specific arabinosidase activity 57-fold and the α-galactosidase activity 6-fold. Other protein fractions with glucosidase (EC 3.2.1.21) and glucanase (EC 3.2.1.6) activity also appeared. According to earlier authors, α-arabinosidases and α-galactosidases are related to alterations in linkages occurring in cell walls, since the enzymes are able to hydrolyze isolated wall polymers. However, our preparations hydrolyze intact cell walls only to a very limited extent, such that their participation in the autolytic processes of cell walls can be ruled out.     

Psychological Changes Accompanying and Mediating Stress-Management Training for Essential Hypertension

In a previous controlled study, 21 participants with essential hypertension were treated with a program based on education, relaxation and D'Zurilla problem-solving training, and another 21 participants were assigned to a waiting list control condition (García-Vera, Labrador, & Sanz, 1997). In this report, the pre-post-treatment psychological changes accompanying those conditions were examined with the Jenkins Activity Survey, the Rosenbaum Self-Control Schedule, the Spielberger State-Trait Anxiety Inventory, and the D'Zurilla-Nezu Social Problem-Solving Inventory. Treatment yielded significant psychological changes that included an increase of problem-solving abilities. Moreover, correlation and multiple regression analyses revealed that, when clinic blood pressure (BP) values were considered, increases in problem-solving abilities were correlated with systolic and diastolic BP reductions for participants in the stress-management condition, and they mediated partially the antihypertensive effects of stress-management training on BP. No significant correlations were found between psychological changes and self-measured systolic or diastolic BP reductions.     

The evolutionary history of Drosophila buzzatii. XXXIV. The distribution of the retrotransposon Osvaldo in original and colonizing populations

The frequency distribution of the retrotransposon Osvaldo in the haploid genome of Drosophila buzzatii has been studied in five natural populations from the Iberian Peninsula and six natural populations from Argentina. In Iberian populations, Osvaldo insertion sites do not follow a Poisson distribution, most probably due to eight euchromatic sites with high occupancy, found in all populations. The estimated alpha and beta parameters, which measure the relative importance of drift and negative selection in shaping frequency distributions, indicate that drift is the main force acting upon the distribution of Osvaldo in natural populations of D. buzzatii in the Iberian Peninsula. On the other hand, Osvaldo distribution in populations from Argentina is similar to the distribution of elements with low copy numbers, such as those described for Drosophila melanogaster and Drosophila simulans: there are no indications for deviation from a Poisson distribution, there is a low occupancy per insertion site, and genetic drift has no apparent effect on the frequency distribution. We propose that the unusual distribution found in the populations from the Iberian Peninsula is a consequence of the colonization process. Iberian Peninsula populations suffered a genomic redistribution of Osvaldo, most probably after a founder effect. Consequently, certain copies that arrived at high frequencies are showing a high occupancies today, and the mean copy number of Osvaldo is higher in Iberian Peninsula populations than in populations from Argentina. All other copies are the result of recent (after colonization) transposition events.     

Effect of osmotic stress on the growth of epicotyls of Cicer arietinum in relation to changes in cell wall composition

The inhibition of growth by polyethlene glycol (PEG)-induced osmotic stress led to modifications in the changes taking place in cell wall composition during normal growth of epicotyls of Cicer arietinum L. cv. Castellana. Epicotyls growing under normal conditions showed a decrease in the amount of pectic fractions and an increase in the hemicellulosic fractions and α-cellulose that led to an increase in the rigidity and a loss in growth capacity. Among the hemicellulosic fractions, the KI-2 fraction (insoluble fraction of 10% KOH-extracted hemicelluloses) seemed to be the only one related to the elongation process and subsequent rigidity. During normal growth a decrease was observed in the total amount of galactose, mainly from the pectic fractions. The inhibition of elongation led to an increase in the amount of the cell walls, due to inhibition of cellular elongation. PEG prevented the increase in the hemicelluloses and the α-cellulose, indicating that these changes were related to elongation. Thus, during the inhibition of elongation there is probably an inhibition of new synthesis that prevents cell wall rigidity and maintains cell wall growth capacity. Changes in the pectic fractions during growth were not affected by the inhibition of elongation, showing that these fractions are related to cell wall loosening rather than to elongation. Study of the cell wall composition confirms the idea that the autolytic process is regulated by changes in the cell wall structure during epicotyl growth     

Nutrients and water availability constrain the seasonality of vegetation activity in a Mediterranean ecosystem

Anthropogenic nitrogen (N) deposition and resulting differences in ecosystem N and phosphorus (P) ratios are expected to impact photosynthetic capacity, that is, maximum gross primary productivity (GPP_max). However, the interplay between N and P availability with other critical resources on seasonal dynamics of ecosystem productivity remains largely unknown. In a Mediterranean tree–grass ecosystem, we established three landscape‐level (24 ha) nutrient addition treatments: N addition (NT), N and P addition (NPT), and a control site (CT). We analyzed the response of ecosystem to altered nutrient stoichiometry using eddy covariance fluxes measurements, satellite observations, and digital repeat photography. A set of metrics, including phenological transition dates (PTDs; timing of green‐up and dry‐down), slopes during green‐up and dry‐down period, and seasonal amplitude, were extracted from time series of GPP_max and used to represent the seasonality of vegetation activity. The seasonal amplitude of GPP_max was higher for NT and NPT than CT, which was attributed to changes in structure and physiology induced by fertilization. PTDs were mainly driven by rainfall and exhibited no significant differences among treatments during the green‐up period. Yet, both fertilized sites senesced earlier during the dry‐down period (17–19 days), which was more pronounced in the NT due to larger evapotranspiration and water usage. Fertilization also resulted in a faster increase in GPP_max during the green‐up period and a sharper decline in GPP_max during the dry‐down period, with less prominent decline response in NPT. Overall, we demonstrated seasonality of vegetation activity was altered after fertilization and the importance of nutrient–water interaction in such water‐limited ecosystems. With the projected warming‐drying trend, the positive effects of N fertilization induced by N deposition on GPP_max may be counteracted by an earlier and faster dry‐down in particular in areas where the N:P ratio increases, with potential impact on the carbon cycle of water‐limited ecosystems.     

ST proteins, a new family of plant tandem repeat proteins with a DUF2775 domain mainly found in Fabaceae and Asteraceae

Background

Many proteins with tandem repeats in their sequence have been described and classified according to the length of the repeats: I) Repeats of short oligopeptides (from 2 to 20 amino acids), including structural cell wall proteins and arabinogalactan proteins. II) Repeats that range in length from 20 to 40 residues, including proteins with a well-established three-dimensional structure often involved in mediating protein-protein interactions. (III) Longer repeats in the order of 100 amino acids that constitute structurally and functionally independent units. Here we analyse ShooT specific (ST) proteins, a family of proteins with tandem repeats of unknown function that were first found in Leguminosae, and their possible similarities to other proteins with tandem repeats.

Results

ST protein sequences were only found in dicotyledonous plants, limited to several plant families, mainly the Fabaceae and the Asteraceae. ST mRNAs accumulate mainly in the roots and under biotic interactions. Most ST proteins have one or several Domain(s) of Unknown Function 2775 (DUF2775). All deduced ST proteins have a signal peptide, indicating that these proteins enter the secretory pathway, and the mature proteins have tandem repeat oligopeptides that share a hexapeptide (E/D)FEPRP followed by 4 partially conserved amino acids, which could determine a putative N-glycosylation signal, and a fully conserved tyrosine. In a phylogenetic tree, the sequences clade according to taxonomic group. A possible involvement in symbiosis and abiotic stress as well as in plant cell elongation is suggested, although different STs could play different roles in plant development.

Conclusions

We describe a new family of proteins called ST whose presence is limited to the plant kingdom, specifically to a few families of dicotyledonous plants. They present 20 to 40 amino acid tandem repeat sequences with different characteristics (signal peptide, DUF2775 domain, conservative repeat regions) from the described group of 20 to 40 amino acid tandem repeat proteins and also from known cell wall proteins with repeat sequences. Several putative roles in plant physiology can be inferred from the characteristics found.     

Sep7 is essential to modify septin ring dynamics and inhibit cell separation during Candida albicans hyphal growth

When Candida albicans yeast cells receive the appropriate stimulus, they switch to hyphal growth, characterized by continuous apical elongation and the inhibition of cell separation. The molecular basis of this inhibition is poorly known, despite its crucial importance for hyphal development. In C. albicans, septins are important for hypha formation and virulence. Here, we used fluorescence recovery after photobleaching analysis to characterize the dynamics of septin rings during yeast and hyphal growth. On hyphal induction, septin rings are converted to a hyphal-specific state, characterized by the presence of a frozen core formed by Sep7/Shs1, Cdc3 and Cdc12, whereas Cdc10 is highly dynamic and oscillates between the ring and the cytoplasm. Conversion of septin rings to the hyphal-specific state inhibits the translocation of Cdc14 phosphatase, which controls cell separation, to the hyphal septum. Modification of septin ring dynamics during hyphal growth is dependent on Sep7 and the hyphal-specific cyclin Hgc1, which partially controls Sep7 phosphorylation status and protein levels. Our results reveal a link between the cell cycle machinery and septin cytoskeleton dynamics, which inhibits cell separation in the filaments and is essential for hyphal morphogenesis.