Faculty of Biology, Genetics, University of Munich, Großhaderner Straße 2-4, 82152, Martinsried, Germany.
The Sainsbury Laboratory, Norwich Research Park, Colney Lane, Norwich, NR4 7UH, UK.
Plant J. 2013 Jul;75(1):117-129. doi: 10.1111/tpj.12220. Epub 2013 Jun 10.
Arbuscular mycorrhiza (AM) fungi form nutrient-acquiring symbioses with the majority of higher plants. Nutrient exchange occurs via arbuscules, highly branched hyphal structures that are formed within root cortical cells. With a view to identifying host genes involved in AM development, we isolated Lotus japonicus AM-defective mutants via a microscopic screen of an ethyl methanesulfonate-mutagenized population. A standardized mapping procedure was developed that facilitated positioning of the defective loci on the genetic map of L. japonicus, and, in five cases, allowed identification of mutants of known symbiotic genes. Two additional mutants representing independent loci did not form mature arbuscules during symbiosis with two divergent AM fungal species, but exhibited signs of premature arbuscule arrest or senescence. Marker gene expression patterns indicated that the two mutants are affected in distinct steps of arbuscule development. Both mutants formed wild-type-like root nodules upon inoculation with Mesorhizobium loti, indicating that the mutated loci are essential during AM but not during root nodule symbiosis.
丛枝菌根（AM）真菌与大多数高等植物形成养分获取共生关系。养分通过丛枝交换，丛枝是在根皮层细胞内形成的高度分支的菌丝结构。为了鉴定参与 AM 发育的宿主基因，我们通过对乙磺酸诱变的群体进行显微镜筛选，分离出了大豆 AM 缺陷突变体。开发了一种标准化的作图程序，便于将缺陷基因座定位在大豆遗传图谱上，在 5 种情况下，还可以鉴定出已知共生基因的突变体。另外 2 个代表独立基因座的突变体在与两种不同的 AM 真菌物种共生时不能形成成熟的丛枝，但表现出丛枝过早停止或衰老的迹象。标记基因表达模式表明，这两个突变体在丛枝发育的不同阶段受到影响。当接种根瘤菌（Mesorhizobium loti）时，这两个突变体都形成了类似于野生型的根瘤，这表明突变基因座在 AM 共生中是必需的，但在根瘤共生中不是必需的。
