Krajinski Franziska, Courty Pierre-Emmanuel, Sieh Daniela, Franken Philipp, Zhang Haoqiang, Bucher Marcel, Gerlach Nina, Kryvoruchko Igor, Zoeller Daniela, Udvardi Michael, Hause Bettina
Max Planck Institute of Molecular Plant Physiology, D-14476 Potsdam (OT) Golm, Germany
Botanical Institute, University of Basel, CH-4056 Basel, Switzerland.
Plant Cell. 2014 Apr;26(4):1808-1817. doi: 10.1105/tpc.113.120436. Epub 2014 Apr 29.
A key feature of arbuscular mycorrhizal symbiosis is improved phosphorus nutrition of the host plant via the mycorrhizal pathway, i.e., the fungal uptake of Pi from the soil and its release from arbuscules within root cells. Efficient transport of Pi from the fungus to plant cells is thought to require a proton gradient across the periarbuscular membrane (PAM) that separates fungal arbuscules from the host cell cytoplasm. Previous studies showed that the H-ATPase gene HA1 is expressed specifically in arbuscule-containing root cells of Medicago truncatula. We isolated a ha1-2 mutant of M. truncatula and found it to be impaired in the development of arbuscules but not in root colonization by Rhizophagus irregularis hyphae. Artificial microRNA silencing of HA1 recapitulated this phenotype, resulting in small and truncated arbuscules. Unlike the wild type, the ha1-2 mutant failed to show a positive growth response to mycorrhizal colonization under Pi-limiting conditions. Uptake experiments confirmed that ha1-2 mutants are unable to take up phosphate via the mycorrhizal pathway. Increased pH in the apoplast of abnormal arbuscule-containing cells of the ha1-2 mutant compared with the wild type suggests that HA1 is crucial for building a proton gradient across the PAM and therefore is indispensible for the transfer of Pi from the fungus to the plant.
丛枝菌根共生的一个关键特征是通过菌根途径改善宿主植物的磷营养，即真菌从土壤中吸收磷并从根细胞内的丛枝中释放磷。磷从真菌向植物细胞的有效转运被认为需要跨围丛枝膜（PAM）的质子梯度，该膜将真菌丛枝与宿主细胞质分开。先前的研究表明，H-ATPase基因HA1在蒺藜苜蓿含丛枝的根细胞中特异性表达。我们分离出了蒺藜苜蓿的ha1-2突变体，发现它在丛枝发育方面受损，但在不规则球囊霉菌丝的根定殖方面未受损。对HA1进行人工microRNA沉默重现了这种表型，导致丛枝小且截断。与野生型不同，ha1-2突变体在低磷条件下对菌根定殖未表现出积极的生长反应。吸收实验证实，ha1-2突变体无法通过菌根途径吸收磷酸盐。与野生型相比，ha1-2突变体含异常丛枝细胞的质外体pH升高，这表明HA1对于跨PAM建立质子梯度至关重要，因此对于磷从真菌向植物的转移是不可或缺的。
