Institute for Biology and Biotechnology of Plants, Westfälische Wilhelms-University, Münster, Germany.
PLoS One. 2013;8(1):e53729. doi: 10.1371/journal.pone.0053729. Epub 2013 Jan 7.
The gene cluster responsible for the biosynthesis of the red polyketidic pigment bikaverin has only been characterized in Fusarium ssp. so far. Recently, a highly homologous but incomplete and nonfunctional bikaverin cluster has been found in the genome of the unrelated phytopathogenic fungus Botrytis cinerea. In this study, we provided evidence that rare B. cinerea strains such as 1750 have a complete and functional cluster comprising the six genes orthologous to Fusarium fujikuroi ffbik1-ffbik6 and do produce bikaverin. Phylogenetic analysis confirmed that the whole cluster was acquired from Fusarium through a horizontal gene transfer (HGT). In the bikaverin-nonproducing strain B05.10, the genes encoding bikaverin biosynthesis enzymes are nonfunctional due to deleterious mutations (bcbik2-3) or missing (bcbik1) but interestingly, the genes encoding the regulatory proteins BcBIK4 and BcBIK5 do not harbor deleterious mutations which suggests that they may still be functional. Heterologous complementation of the F. fujikuroi Δffbik4 mutant confirmed that bcbik4 of strain B05.10 is indeed fully functional. Deletion of bcvel1 in the pink strain 1750 resulted in loss of bikaverin and overproduction of melanin indicating that the VELVET protein BcVEL1 regulates the biosynthesis of the two pigments in an opposite manner. Although strain 1750 itself expresses a truncated BcVEL1 protein (100 instead of 575 aa) that is nonfunctional with regard to sclerotia formation, virulence and oxalic acid formation, it is sufficient to regulate pigment biosynthesis (bikaverin and melanin) and fenhexamid HydR2 type of resistance. Finally, a genetic cross between strain 1750 and a bikaverin-nonproducing strain sensitive to fenhexamid revealed that the functional bikaverin cluster is genetically linked to the HydR2 locus.
迄今为止，负责生物合成红色聚酮类色素比咯并喹啉酮的基因簇仅在尖孢镰刀菌属中得到了描述。最近，在不相关的植物病原菌 Botrytis cinerea 的基因组中发现了一个高度同源但不完整且无功能的比咯并喹啉酮簇。在这项研究中，我们提供的证据表明，像 1750 这样的稀有 Botrytis cinerea 菌株具有一个完整且功能齐全的簇，该簇包含与 Fusarium fujikuroi ffbik1-ffbik6 同源的 6 个基因，并确实产生比咯并喹啉酮。系统发育分析证实，整个簇是通过水平基因转移（HGT）从 Fusarium 获得的。在不产生比咯并喹啉酮的菌株 B05.10 中，编码比咯并喹啉酮生物合成酶的基因由于有害突变（bcbik2-3）或缺失（bcbik1）而失去功能，但有趣的是，编码调节蛋白 BcBIK4 和 BcBIK5 的基因没有携带有害突变，这表明它们可能仍然具有功能。F. fujikuroi Δffbik4 突变体的异源互补证实了菌株 B05.10 的 bcbik4 确实完全功能。在粉红色菌株 1750 中删除 bcvel1 导致比咯并喹啉酮的缺失和黑色素的过度产生，表明 VELVET 蛋白 BcVEL1 以相反的方式调节这两种色素的生物合成。尽管菌株 1750 自身表达一种截断的 BcVEL1 蛋白（100 而不是 575 aa），该蛋白在形成菌核、毒力和草酸形成方面无功能，但足以调节色素生物合成（比咯并喹啉酮和黑色素）和 Fenhexamid HydR2 型抗性。最后，在菌株 1750 和对 Fenhexamid 敏感的不产生比咯并喹啉酮的菌株之间进行遗传杂交表明，功能齐全的比咯并喹啉酮簇与 HydR2 基因座在遗传上相关。
