Characterization of a pathogenesis-related gene family induced in rice during infection with Magnaporthe grisea
Abstract
Rice cDNAs whose genes exhibited elevated expression during rice blast infection have been isolated by differential screening (Talbot et al 1993). One of these cDNAs, MAG-7, was chosen as a source of a Magnaporthe-induced promoter. MAG-7 was found to share homology with a known class of PR proteins found in a variety of plants (PR-10 proteins; Van Loon et al 1994). Southern hybridization of rice genomic DNA (varieties Co39, IR36, and IR54) probed with the MAG-7 cDNA indicated that these varieties contain multiple copies of the MAG-7 gene (2-5 copies) per haploid genome. A 16 kb genomic clone isolated from a Co39 genomic library was found to contain three copies of the MAG-7 gene. These genes were named RPR10a, RPR10b, and RPR10c. RPR10a was sequenced in its entirety including ca. 1.4 kb of the 5$\sp\prime$ promoter region. This gene shares 100% homology to the MAG-7 cDNA. The remaining two genes, RPR10b and RPR10c, have been partially sequenced. Gene-specific probes were constructed to observe transcriptional differences between the three RPR10 genes in Northern blots of total RNA isolated from Co39 seedling leaves at 0, 12, 18, 24, 36, 48, 72, and 144 hours after infection with M. grisea. Transcripts of RPR10a were found to be induced from a low basal level within 12 hours following M. grisea infection, with increasing accumulation through 144 hours of induction. Transcripts of RPR10b were also enhanced by M. grisea, although RPR10b induction appeared later than RPR10a and was first strongly visible at 48 hours post inoculation. Unlike RPR10a and b, RPR10c exhibited no signs of induction by M. grisea in RNA samples isolated from infected rice leaves throughout the 144 hour time period. Tissue prints of M. grisea infected Co39 leaves were made using the RPR10a gene-specific probe. Hybridization of the rice PR-10a probe was found to occur only at the site of infection and illustrates that the rice PR-10a transcript is induced in a localized fashion by M. grisea.
Degree
Ph.D.
Advisors
Hodges, Purdue University.
Subject Area
Plant pathology|Genetics|Molecular biology
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