Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2001
Publication Date: N/A
Interpretive Summary: DNA fingerprinting has been used extensively to characterize populations of Mycosphaerella graminicola, the septoria tritici blotch pathogen of wheat. However, nothing is known about the reason for DNA fingerprint patterns in this fungus. One likely explanation is that the DNA fingerprints are due to transposable elements, pieces of DNA that are capable of moving from one epart of the genome to another. Transposable elements are important becaus they can increase the level of genetic variation in an organism, which can increase their rate of evolution. Plant pathogenic fungi that contain transposable elements might be more likely to develop resistance to fungicides, or to overcome host resistance genes. Furthermore, transposable elements that move actively can be developed as tools for genetic analyses of fungi and other organisms. To test the hypothesis that DNA fingerprints in M. graminicola are due to transposable elements, a DNA fingerprint probe eand related clones were sequenced and subjected to genetic analysis. Thes analyses indicated that the DNA fingerprint probe from M. graminicola contained part of a transposable element that was active during both sexual and asexual reproduction, that the transposable element is different from others identified previously and that it may have been acquired by the fungus recently. These results will be useful to plant pathologists who use DNA fingerprinting to characterize populations of this fungus, because it means that DNA fingerprint results must be interpreted cautiously. Geneticists may be able to develop this transposable element into a tool to further analyze the genetics of this organism. The transposable element also may be useful to other scientists for analyzing the genetics of organisms which do not contain transposable elements.
Technical Abstract: DNA fingerprinting has been used extensively to characterize populations of Mycosphaerella graminicola, the septoria tritici blotch pathogen of wheat. To test the hypothesis that the DNA fingerprint probe pSTL70 recognizes a transposable element, the clone was sequenced, along with three others that hybridized with pSTL70. These analyses revealed that pSTL70 probably is a chimera, part of which contains the 5' end of a probable histidine kinase gene. The remaining portion contains the 3' end of a reverse transcriptase sequence plus 29 and 79 base pair direct repeats. These are characteristic of transposable elements identified in other organisms. Southern analysis with only the reverse transcriptase or the direct repeat sequences as probe duplicated the original DNA fingerprint pattern. Progeny isolates were analyzed to test whether the transposable element was active during sexual and asexual reproduction. Analysis of 60 progeny from a cross between two Dutch isolates of M. graminicola identified many new bands that were not present in the parents. Thus, the putative transposable element is active during meiosis. To test for movement during asexual reproduction, ten 10-generation single-spore lines were obtained from each of the two parents of the mating population. The ten lines derived from one parent showed no changes after 100 generations of asexual reproduction. However, four of the ten A10 lines from isolate IPO 94269 showed a gain or loss of one or more DNA fingerprint bands. These changes were confirmed by analysis of five additional isolates from the tenth generation of each line. These results indicate that the DNA fingerprint probe pSTL70 identifies a transposable element in M. graminicola that appears to be active during both sexual and asexual reproduction.