Temperature Influenced Regulation of Adenosine 3′, 5′ - cyclic Monophosphate Dependent Protein Kinase A in Magnaporthe grisea (T.T. Hebert), M. E. Barr

Abstract

For leaf blast pathogen (Magnaporthe grisea), surface features exerted significant influence on conidia germination and appressorium formation. However, external application of cyclic adenosine monophosphate (cAMP) could significantly nullify the temperature effect on appressorium formation and partially neutralize the difference of surface. Protein kinase A (PKA) activity was significantly higher at 29 °C as compared to that of 22 °C, and at 34 °C no activity was detected. MPG gene expressed during appressorium formation was found to be influenced by temperature as expression level of MPG gene was almost 44 folds at 29 °C and 34 folds at 22 °C in comparison to that of 16 °C. Morphogenesis of conidial germ tube tip into appressorium was significantly reduced by external glycerol application (2.5% or above) and germ tube continued to grow without formation of appressorium. Thus, cAMP regulated PKA activity was responsible for high endogenous glycerol concentration inside the tip cell of the germ tube where glycerol acted as potential solute for water influx from the host surface through osmosis. Blast pathogenicity is a process regulated by cAMP-dependent PKA activity, modified by temperature influence and manifestation of appressorium which occurs due to influx of water from the surface.