Mtha1, a plasma membrane H+-ATPase gene from Medicago truncatula, shows arbuscule-specific induced expression in mycorrhizal tissue

Transport processes between plant and fungal cells are key elements in arbuscular mycorrhiza (AM), where H+-ATPases are considered to be involved in active uptake of nutrients from the symbiotic interface. Genes encoding H+-ATPases were identified in the genome of Medicago truncatula and three cDNA fragments of the H+-ATPase gene family (Mtha1-3) were obtained by RT-PCR using RNA from M. truncatula mycorrhizal roots as template. While Mtha2 and Mtha3 appeared to be constitutively expressed in roots and unaffected by AM development, transcripts of Mtha1 could only be detected in AM tissues and not in controls. Further analyses by RT-PCR revealed that Mtha1 transcripts are not detectable in shoots and phosphate availability did not affect RNA accumulation of the gene. Localization of transcripts by in situ hybridization on AM tissues showed that Mtha1 RNA accumulates only in cells containing fungal arbuscules. This is the first report of arbuscule-specific induced expression of a plant H+-ATPase gene in mycorrhizal tissues.