Arbuscular mycorrhiza development regulates the mRNA abundance of Mtaqp1 encoding a mercury-insensitive aquaporin of Medicago truncatula

The genome of the model legume Medicago truncatula Gaertn. was screened for the presence of genes encoding tonoplast intrinsic proteins, and a gene fa mily was identified. The cDNA fragments of two members of the multigene fam ily were cloned from roots inoculated with an arbuscular mycorrhizal fungus . Transcript accumulation in roots could be detected for both cDNA fragment s, but only one gene was induced in the symbiosis when compared to nonmycor rhizal control roots. A full-length cDNA clone was obtained from the arbusc ular-mycorrhiza-regula ted gene, and injection of in-vitro-transcribed RNA into Xenopus oocytes revealed that the encoded protein MtAQP1 specifically facilitates water transport. The possible role of MtAQP1 in buffering osmot ic fluctations in the highly compartmented vacuole of arbuscule cells is di scussed.