Hubberten Hans-Michael, Sieh Daniela, Zöller Daniela, Hoefgen Rainer, Krajinski Franziska
a Max-Planck-Institute of Molecular Plant Physiology ; Potsdam-Golm , Germany.
Plant Signal Behav. 2015;10(6):e989025. doi: 10.4161/15592324.2014.989025.
Bidirectional nutrient transfer is one of the key features of the arbuscular mycorrhizal symbiosis. Recently we were able to identify a Medicago truncatula mutant (mtha1-2) that is defective in the uptake of phosphate from the periarbuscular space due to a lack of the energy providing proton gradient provided by the symbiosis specific proton ATPase MtHA1 In order to further characterize the impact of fungal colonization on the plant metabolic status, without the beneficial aspect of improved mineral nutrition, we performed leaf ion analyses in mutant and wildtype plants with and without fungal colonization. Although frequency of fungal colonization was unaltered, the mutant did not show a positive growth response to mycorrhizal colonization. This indicates that nutrient transfer into the plant cell fails in the truncated arbuscules due to lacking expression of a functional MtHA1 protein. The leaves of wildtype plants showed clear metabolic responses to root mycorrhizal colonization, whereas no changes of leaf metabolite levels of mycorrhizal mtha1-2 plants were detected, even though they were colonized. These results show that MtHa1 is indispensable for a functional mycorrhizal symbiosis and, moreover, suggest that fungal root colonization per se does not depend on nutrient transfer to the plant host.
双向养分转移是丛枝菌根共生的关键特征之一。最近，我们鉴定出一种蒺藜苜蓿突变体（mtha1-2），由于缺乏共生特异性质子ATP酶MtHA1提供的能量供应质子梯度，该突变体在从丛枝周隙吸收磷酸盐方面存在缺陷。为了进一步表征真菌定殖对植物代谢状态的影响，而不考虑改善矿物质营养这一有益方面，我们对有无真菌定殖的突变体和野生型植物进行了叶片离子分析。尽管真菌定殖频率未改变，但该突变体对菌根定殖未表现出积极的生长反应。这表明由于缺乏功能性MtHA1蛋白的表达，营养物质向植物细胞的转移在截断的丛枝中失败。野生型植物的叶片对根部菌根定殖表现出明显的代谢反应，而尽管菌根化的mtha1-2植物已被定殖，但未检测到其叶片代谢物水平的变化。这些结果表明，MtHa1对于功能性菌根共生是不可或缺的，此外，还表明真菌根部定殖本身并不依赖于向植物宿主的养分转移。
