FIGURE 3.

Complementation of ammonium uptake deficiency in a yeast triple mutant by glomeromycotan AMTs. Ammonium uptake-deficient yeast cells (mep1–3Δ) were transformed with an expression vector containing various AMT genes under control of the strong PMA1 promoter. Fivefold dilution series of the transformants were incubated either on minimal medium containing 50 μM (NH₄)₂SO₄ (=100 μM NH₄⁺) as sole nitrogen source for 16 days (left) or on synthetic complete medium [containing roughly 37.5 mM (NH₄)₂SO₄] for 3 days (right). Rhizophagus irregularis AMTs are able to partly complement the growth deficiency of the Δmep1–3 yeast mutant on low NH₄⁺ concentrations (100 μM, left).