The role of cutinase in germling development and infection by Erysiphe graminis f sp hordei

We have investigated the importance of cutinase in the germination of Erysiphe graminis f.sp. hordei conidia, specifically in the induction of appressorial germ tube (AGT) formation and penetration of the host cuticle. When cutin monomers were coated onto glass microscope slides or plastic coverslips, the percentage of AGT differentiation in germinating conidia dramatically increased. This suggests that cutin monomers act as a signal to trigger AGT development. The esterase inhibitors ebelactone A and ebelactone B inhibited E. graminis cutinase activity in germinated spores in microtitre plate wells. Low concentrations of ebelactones did not affect spore germination and AGT differentiation on cellulose dialysis membrane, an artificial surface on which germling morphogenesis is normal to the AGT stage. However, AGT formation on ebelactone-treated barley leaves was significantly lower than on cellulose. Inhibition of cutinase by ebelactones may have prevented cutin monomers being released from the cuticle and thus affected germling development on the leaf. Ebelactones applied to leaves also prevented infection of the host and development of mature sporulating colonies. These results suggest that cutinase plays an important role in the pathogenicity of E. graminis and may affect germination as well as cuticular penetration. (C) 1996 Academic Press Limited.