STAGE-SPECIFIC GENE-EXPRESSION DURING APPRESSORIUM FORMATION OF MAGNAPORTHE-GRISEA

Lee, Y.-H., and Dean, R. A. 1993. Stage-specific gene expression during appressorium formation of Magnaporthe grisea. Experimental Mycology 17, 215-222. Magnaporthe grisea, the rice blast pathogen, develops specialized infection structures to infect plants. Following germination of conidia on a plant surface, extension of the germ tube ceases and the tip swells to form an appressorium, a darkly pigmented adhesion structure. Subsequently, an infection hypha emerges that penetrates through the cuticle and cell wall of epidermal cells. To begin to elucidate the mechanism of infection, genes expressed during early stages of differentiation following germination were isolated by differential screening of a genomic DNA library of strain 70-15. 32P-labeled cDNA probes were prepared from poly(A)+ RNA isolated from M. grisea induced to form appressoria and from undifferentiated germlings. Several clones were found to contain genes that were highly expressed during appressorium formation. Northern blot analyses of two clones, 28C6 and 29G11, indicated that both contained genes within EcoRI fragments (5.0 and 8.0 kb, respectively) stage-specifically expressed during appressorium formation. These genes designated mif23 (28C6) and mif29 (29G11) (Magnaporthe infection) have transcript sizes of approximately 1.2 and 3.1 kb, respectively. Gel blot analysis of chromosome DNA indicates that these genes are present as single copies in the haploid genome of M. grisea. © 1993 Academic Press. All rights reserved.