Enhanced biocontrol activity of Trichoderma virens transformants constitutively coexpressing β-1,3- and β-1,6-glucanase genes

Evidence for the role of chitinases, proteases and β-1,3- and β-1,6-glucanases in mycoparasitism by Trichoderma species has been well documented. Moreover, constitutive over-expression of genes encoding individual cell-wall-degrading enzymes (CWDEs) has been shown to improve the potential of biological agents. In this study, we generated transformants of T. virens in which β-1,3- and β-1,6-glucanase genes, TvBgn2 and TvBgn3 , respectively, were constitutively coexpressed in the same genetic T. virens Gv29.8 wild-type background. The double over-expression transformants (dOEs) grow and sporulate slower than the wild-type (WT). However, the reduction in growth did not seem to affect their mycoparasitic and biocontrol capabilities, as dOEs displayed much higher levels of total β-1,3- and β-1,6-glucanase activity than the WT. This higher enzymatic activity of dOEs positively correlated with observed in vitro inhibition of Pythium ultimum and Rhizoctonia solani mycelia, and with enhanced bioprotection of cotton seedlings against P. ultimum , R. solani and Rhizopus oryzae . Besides effective biocontrol of all pathogens at an original inoculum level, the performance of dOEs was highly enhanced (up to 312% of WT performance) when pathogen pressure was greater (i.e. concentration of inoculum was higher or pathogens applied in combination). These results demonstrate that the strategy of introducing multiple lytic enzyme-encoding genes through transformation of a given biocontrol strain can be successfully used to achieve better biocontrol.     

Meiosis reinitiation in molluscan oocytes: a model to study the transduction of extracellular signals

Summary

G2-arrested marine invertebrate oocytes are triggered to reenter the cell cycle by different extracellular signals (sperm, hormones and mimetics). They respond to competent signals either by germinal vesicle breakdown (for those arrested in prophase I) or by polar body emission (for those arrested in metaphase I or II). These cellular responses are easy to observe and quantify thus making of meiosis reinitiation an attractive model to study the transduction of signals endogenous to oocytes. Given the universal character of transmembrane coupling molecules and intracellular effectors, the specificity of cell and, in particular, oocyte response to an extracellular signal are mediated by the presence of specific receptors and by a specific set of intracellular effectors that are activated by them. In this paper we discuss the current limitations in molecular and pharmacological identification and characterization of invertebrate oocyte receptors. We next analyze signalling pathways triggered by activation of relevant receptors and the cross-talk existing between them. The above aspects are discussed on the examples of serotonin-induced meiosis reinitiation in prophase I-arrested oocytes of Spisula solidissima and on KCl-induced meiosis reinitiation of metaphase I-arrested Mytilus galloprovincialis oocytes taken as paradigms.