Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Plant Cell Physiol. 2010 Sep;51(9):1425-35. doi: 10.1093/pcp/pcq115. Epub 2010 Aug 23.
Nitrogen fixation in nodules that contain symbiotic rhizobial bacteria enables legumes to thrive in nitrogen-poor soils. However, this symbiosis is energy consuming. Therefore, legumes strictly control nodulation at both local and systemic levels. Mutants deficient in such controls exhibit a range of phenotypes from non-nodulation to hypernodulation. Here, we isolated a novel hypernodulation mutant from the M(2) progeny derived from Lotus japonicus MG-20 seeds mutagenized by irradiation with a carbon ion beam. We named the mutant 'plenty' because it formed more nodules than the wild-type MG-20. The nodulation zone in the plenty mutant was wider than that in the wild type, but not as enhanced as those in other previously reported hypernodulation mutants such as har1, klv or tml of L. japonicus. Unlike these hypernodulation mutants, the plenty mutant developed nodules of the same size as MG-20. Overall, the plenty mutant exhibited a unique phenotype of moderate hypernodulation. However, a biomass assay indicated that this unique pattern of hypernodulation was a hindrance to host plant growth. The plenty mutant displayed some tolerance to external nitrates and a normal triple response to ethylene. Grafting experiments demonstrated that the root of plenty was responsible for its hypernodulation phenotype. Genetic mapping indicated that the PLENTY gene was located on chromosome 2.
根瘤中的共生根瘤菌固氮使豆科植物能够在氮素贫瘠的土壤中茁壮成长。然而，这种共生关系是耗能的。因此，豆科植物严格控制局部和系统水平的结瘤。缺乏这种控制的突变体表现出从不结瘤到过度结瘤的一系列表型。在这里，我们从用碳离子束辐照诱变的日本绿豆 MG-20 种子的 M(2)后代中分离到一个新的过度结瘤突变体。我们将突变体命名为“丰富”，因为它比野生型 MG-20 形成更多的根瘤。丰富突变体的结瘤区比野生型宽，但不如其他先前报道的过度结瘤突变体如日本绿豆 har1、klv 或 tml 那样增强。与这些过度结瘤突变体不同，丰富突变体形成的根瘤与 MG-20 一样大。总的来说，丰富突变体表现出中等过度结瘤的独特表型。然而，生物量测定表明，这种独特的过度结瘤模式阻碍了宿主植物的生长。丰富突变体对外部硝酸盐表现出一定的耐受性和对乙烯的正常三重反应。嫁接实验表明，丰富的根是其过度结瘤表型的原因。遗传图谱表明，PLENTY 基因位于染色体 2 上。
