The complete DNA sequence of the nuclear ribosomal RNA gene complex of Verticillium dahliae

摘要

The genus Verticillium contains a heterogeneous assemblage of asexual fungi, many of which are important plant pathogens or entomopathogens. The status of Verticillium species had remained unclear, until techniques for molecular biology proved quitean aid in understanding the genetic diversity in the genus (1, 17). Considerable progress has been made in just the last few years in identification of species and subspecific groups, based on differences in DNA sequences (4, 9, 10, 14). Nucleic acid sequencing technology proved to be an exceptional tool in identification and diagnosis but also for assessing evolutionary relatedness, because sequence data permit straightforward, quantitative interpretation, and they form a growing data base for subsequent reference (12). In this respect, rDNAs are at present the most used of the molecular chronometers in the delineation of evolutionary and phylogenetic relations. Genes of rRNA molecules occur in all organisms, have constant function, lack artifacts ofhorizontal transfer between organisms and most of all, are technically feasible to analyze. Additionally, the different degree of sequence conservation met in different parts of these molecules, permits the examination of the evolution time-scale at almost any different level of magnification (6). For this study, the complete sequence of the rDNA gene complex of a Greek Verticillium dahliae Kleb. isolate, pathogenic to cotton, has been analyzed and is presented. It should be pointed out that parts of the rDNA gene complex of V. dahliae have been already sequenced by other research groups (5, 7, 8, 13). However, the aim of this work was dual: first, to provide the complete sequence of the rDNA gene complex for more accurate, comparative studies and second, to form the basis for sequence comparisons by which small insertions of the different intron types already found in other filamentous fungi (11) would also be detected in V. dahliae.