title: Multiple group I introns in the small-subunit rDNA of Botryosphaeria dothidea: implication for intraspecific genetic diversity.
abstract: Botryosphaeria dothidea is a widespread and economically important pathogen on various fruit trees, and it often causes die-back and canker on limbs and fruit rot. In characterizing intraspecies genetic variation within this fungus, group I introns, rich in rDNA of fungi, may provide a productive region for exploration. In this research, we analysed complete small subunit (SSU) ribosomal DNA (rDNA) sequences of 37 B. dothidea strains, and found four insertions, designated Bdo.S943, Bdo.S1199-A, Bdo.S1199-B and Bdo.S1506, at three positions. Sequence analysis and structure prediction revealed that both Bdo.S943 and Bdo.S1506 belonged to subgroup IC1 of group I introns, whereas Bdo.S1199-A and Bdo.S1199-B corresponded to group IE introns. Moreover, Bdo.S1199-A was found to host an open reading frame (ORF) for encoding the homing endonuclease (HE), whereas Bdo.S1199-B, an evolutionary descendant of Bdo.S1199-A, included a degenerate HE. The above four introns were novel, and were the first group I introns observed and characterized in this species. Differential distribution of these introns revealed that all strains could be separated into four genotypes. Genotype III (no intron) and genotype IV (Bdo.S1199-B) were each found in only one strain, whereas genotype I (Bdo.S1199-A) and genotype II (Bdo.S943 and Bdo.S1506) occurred in 95% of the strains. There is a correlation between B. dothidea genotypes and hosts or geographic locations. Thus, these newly discovered group I introns can help to advance understanding of genetic differentiation within B. dothidea.
authors.affiliation: Key Laboratory of Crop Stress Biology in Arid Areas, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Xu
authors.forename: Chunsheng
authors.initials: C
authors.lastname: Wang
authors.forename: Xinyao
authors.initials: X
authors.lastname: Sun
authors.forename: Rong
authors.initials: R
authors.lastname: Zhang
authors.forename: Mark L
authors.initials: ML
authors.lastname: Gleason
authors.forename: Tanaka
authors.initials: T
authors.lastname: Eiji
authors.forename: Guangyu
authors.initials: G
authors.lastname: Sun
mesh_terms: D000595:Amino Acid Sequence; D001203:Ascomycota / Q000145:classification / Q000235:genetics*; D001483:Base Sequence; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics*; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics*; D004720:Endonucleases / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics; D014644:Genetic Variation; D007438:Introns / Q000235:genetics*; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D004271:DNA, Fungal; D004275:DNA, Ribosomal; D005656:Fungal Proteins; D004720:Endonucleases