Boty-II, a novel LTR retrotransposon in Botrytis cinerea B05.10 revealed by genomic sequence

Botrytis cinerea is a necrotrophic pathogen causing pre- and post-harvest diseases in at least 235 plant species. It manifests extraordinary genotype and phenotype variation. One of the causes of this variation is transposable elements. Two transposable elements have been discovered in this fungus, the retrotransposon (Boty), and the transposon (Flipper). In this work, two complete (Boty-II-76 and Boty-II-103) and two partial (Boty-II-95 and Boty-II-141) long terminal repeat (LTR) retrotransposons were identified by an in silico genomic sequence analysis. Boty-II-76 and Boty-II-103 contain 6439 bp nucleotides with a pair of LTRs at both ends, and an internal deduced pol gene encoding a polyprotein with reverse transcriptase and DDE integrase domains. They are flanked by 5 bp direct repeats (ACCAT, CTTTC). In Boty-II-141, two LTRs at both ends, and a partial internal pol gene encoding a protein with a DDE integrase domain were identified. In Boty-II-95, a right LTR and a partial internal pol gene encoding a protein with no conserved domains were identified. Boty-II uses a self-priming mechanism to initiate synthesis of reverse transcripts. The sequence of the presumed primer binding site for first-strand reverse transcription is 5’-TTGTACCAT-3’. The polypurine-rich sequence for plus-strand DNA synthesis is 5’-GCCTTGAGCGGGGGGTAC-3’. Fourteen Boty-II LTRs that contain 125-158 bp nucleotides and share 69.1 ~ 100 percent identities with the short inverted terminal repeats of 5 bp (TGTCA…TGACA) were discovered. Analysis of structural features and phylogeny revealed that Boty-II is a novel LTR retrotransposon. It could potentially be used as a novel molecular marker for the investigation of genetic variation in B. cinerea.

Two LTR retrotransposon elements within the abscisic acid gene cluster in Botrytis cinerea B05.10, but not in SAS56

The plant hormone abscisic acid has huge economic potential and can be applied in agriculture and forestry for it is considered to be involved in plant resistance to stresses such as cold, heat, salinity, drought, pathogens and wounding. Now overproducing strains of Botrytis cinerea are used for biotechnological production of abscisic acid. An LTR retrotransposon, Boty-aba, and a solo LTR were identified by in silico genomic sequence analysis, and both were detected within the abscisic acid gene cluster in B. cinerea B05.10, but not in B. cinerea SAS56. Boty-aba contains a pair of LTRs and two internal genes. The LTRs and the first gene have features characteristic of Ty3/gypsy LTR retrotransposons. The second gene is a novel gene, named brtn, which encodes for a protein (named BRTN) without putative conserved domains. The impressive divergence in structure of the abscisic acid gene clusters putatively gives new clues to investigate the divergence in the abscisic acid production yields of different B. cinerea strains.