CGT1 - A NON-LTR RETROTRANSPOSON WITH RESTRICTED DISTRIBUTION IN THE FUNGAL PHYTOPATHOGEN COLLETOTRICHUM-GLOEOSPORIOIDES

Two genetically distinct biotypes (A and B) of Colletotrichum gloeospo rioides that cause different anthracnose diseases on the legumes Stylo santhes spp. have been identified in Australia. A DNA sequence that wa s present in biotype B and absent in biotype A was isolated by differe ntial hybridisation of a genomic library using total genomic DNA of ea ch biotype as hybridisation probes. This sequence also failed to hybri dise to DNA of three biotypes of C, gloeosporioides from other host sp ecies and to DNA of three other species of Colletotrichum. This clone was used to isolate two cosmid clones of biotype B. Sequence analysis of these clones revealed a repetitive element of approximately 5.7 kb in length, This element, termed CgT1, Nas dispersed in the genome and present in about 30 copies. The element contained open reading frames encoding deduced sequence motifs homologous to gag-like proteins, reve rse transcriptase and RNase H domains of non-LTR retrotransposons. The termini of CgT1 lacked long terminal repeals (LTRs) but contained a 3 ' A-rich domain, The insertion site of one copy of the element was fla nked by short 13-bp direct repeats, These characteristics of the termi ni taken together with the overall structure and sequence homologies, indicate that CgT1 belongs to the non-LTR, LINE-like retrotransposon c lass of elements that are present in many eukaryotes, PCR primers desi gned to amplify regions of CgT1 call be used to distinguish biotypes A and B in Australia. DNA fingerprinting analysis of genomic DNA using hybridisation probes derived from the terminal regions of CgT1 reveale d that Australian isolates of biotype B are monomorphic. CgT1 was not detected in some isolates causing Type B disease from other countries and when CgT1 was present there was considerable polymorphism in COTI organisation in the genome. CgT1 is the first transposon-like element to be identified in the genus Colletotrichum and has considerable pote ntial as a tool for the study of population structure, genome dynamics and evolution in C. gloeosporioides.