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 germin ating conidia dramatically increased. This suggests that cutin monomer s 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 o n cellulose dialysis membrane, an artificial surface on which germling morphogenesis is normal to the AGT stage. However, AGT formation on e belactone-treated barley leaves was significantly lower than on cellul ose. Inhibition of cutinase by ebelactones may have prevented cutin mo nomers being released from the cuticle and thus affected germling deve lopment on the leaf. Ebelactones applied to leaves also prevented infe ction of the host and development of mature sporulating colonies. Thes e results suggest that cutinase plays an important role in the pathoge nicity of E. graminis and may affect germination as well as cuticular penetration. (C) 1996 Academic Press Limited.