Symbiotic status, phosphate, and sucrose regulate the expression of two plasma membrane H⁺-ATPase genes from the mycorrhizal fungus Glomus mosseae

The establishment of the arbuscular mycorrhizal symbiosis results in a modification of the gene expression pattern in both plant and fungus to accomplish the morphological and physiological changes necessary for the bidirectional transfer of nutrients between symbionts. H(+)-ATPase enzymes play a key role establishing the electrochemical gradient required for the transfer of nutrients across the plasma membrane in both fungi and plants. Molecular analysis of the genetic changes in arbuscular mycorrhizal fungi during symbiosis allowed us to isolate a fungal cDNA clone encoding a H(+)-ATPase, GmPMA1, from Glomus mosseae (BEG12). Despite the high conservation of the catalytic domain from H(+)-ATPases, detailed analyses showed that GmPMA1 was strongly related only to a previously identified G. mosseae ATPase gene, GmHA5, and not to the other four ATPase genes known from this fungus. A developmentally regulated expression pattern could be shown for both genes, GmPMA1 and GmHA5. GmPMA1 was highly expressed during asymbiotic development, and its expression did not change when entering into symbiosis, whereas the GmHA5 transcript was induced upon plant recognition at the appressorium stage. Both genes maintained high levels of expression during intraradical development, but their expression was reduced in the extraradical mycelium. Phosphate, a key nutrient to the symbiosis, also induced the expression of GmHA5 during asymbiotic growth, whereas sucrose had a negative effect. Our results indicate that different fungal H(+)-ATPases isoforms might be recruited at different developmental stages possibly responding to the different requirements of the life in symbiosis.