Differentiated functions of Ras1 and Ras2 proteins in regulating the germination, growth, conidiation, multi-stress tolerance and virulence ofBeauveria bassiana

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SummaryRas1 and Ras2 are two distinct Ras GTPases inBeauveria bassiana, an entomopathogenic fungus whose biocontrol potential against insect pests depends largely on virulence and multi-stress tolerance. The functions of both proteins were characterized for the first time by constructing dominant-active (GTP-bound)Ras1G19Vand dominant-negative (GDP-bound)Ras1D126Aand integrating them and normalRas1into wild type and ΔRas2for a series of phenotypic and transcriptional analyses. The resultant mutants showed gradient changes of multiple phenotypes but little difference in conidial thermotolerance. Expression ofRas1D126Acaused vigorous hyphal growth, severely defective conidiation, and increased tolerances to oxidation, cell wall disturbance, fungicide and UV-A/UV-B irradiations, but affected slightly germination, osmosensitivity and virulence. These phenotypes were antagonistically altered by mRas1G19Vexpressed in either wild type or ΔRas2, which was severely defective in conidial germination and hyphal growth and displayed intermediate changes in other mentioned phenotypes between paired mutants expressingRas1G19VorRas1D126Ain wild type and ΔRas2. Their growth, UV tolerance or virulence was significantly correlated with cellular response to oxidation or cell wall disturbance. Transcriptional changes of 35 downstream effector genes involved in conidiation and multi-stress responses also related to most of the phenotypic changes among the mutants. Our findings highlight that Ras1 and Ras2 regulate differentially or antagonistically the germination, growth, conidiation, multi-stress tolerance and virulence ofB. bassiana, thereby exerting profound effects on the fungal biocontrol potential.

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