Cloning and analysis of the mating-type idiomorphs from the barley pathogen Septoria passerinii

详细信息    查看全文

• 作者：S. B. Goodwin ; C. Waalwijk ; G. H. J. Kema ; J. R. Cavaletto and G. Zhang
• 刊名：Molecular Genetics and Genomics
• 出版年：2003
• 出版时间：April 2003
• 年：2003
• 卷：269
• 期：1
• 页码：1-12
• 全文大小：702 KB

文摘

The genus Septoria contains more than 1000 species of plant pathogenic fungi, most of which have no known sexual stage. Species of Septoria without a known sexual stage could be recent derivatives of sexual species that have lost the ability to mate. To test this hypothesis, the mating-type region of S. passerinii, a species with no known sexual stage, was cloned, sequenced, and compared to that of its close relative S. tritici (sexual stage: Mycosphaerella graminicola). Both of the S. passerinii mating-type idiomorphs were approximately 3 kb in size and contained a single reading frame interrupted by one (MAT-2) or two (MAT-1) putative introns. The putative products of MAT-1 and MAT-2 are characterized by alpha-box and high-mobility-group sequences, respectively, similar to those in the mating-type genes of M. graminicola and other fungi. The mating-type genes of S. passerinii and M. graminicola are evolving rapidly, approximately ten times faster than the internal transcribed spacer region of the ribosomal DNA, and are not closely related to those from Cochliobolus or other loculoascomycetes in the order Pleosporales. Therefore, the class Loculoascomycetes may be polyphyletic. Furthermore, differences between the phylogenetic trees may indicate separate evolutionary histories for the MAT-1 and MAT-2 idiomorphs. A three-primer multiplex-PCR technique was developed that allowed rapid identification of the mating types of isolates of S. passerinii. Both mating types were present in approximately equal frequencies and often on the same leaf in fields in Minnesota and North Dakota. Analyses with isozyme and random amplified polymorphic DNA markers revealed that each isolate had a unique genotype. The common occurrence of both mating types on the same leaf and the high levels of genotypic diversity indicate that S. passerinii is almost certainly not an asexual derivative of a sexual fungus. Instead, sexual reproduction probably plays an integral role in the life cycle of S. passerinii and may be much more important than previously believed in this (and possibly other) "asexual" species of Septoria.