Premature expression of ros1 triggers an early arrest of filamentous growth and induces septation.

Maize seedlings were infected with a combination of FB1 x FB2 (A, B) or FB1Δros1_Pmig2-6Ros1 x FB2Δros1_Pmig2-6Ros1 strains expressing ros1 from the mig2-6 promoter which is induced two days after colonization (C, D). A and C show macroscopic symptoms on leaves at 8 dpi. Only very small tumors are visible on plants infected with FB1Δros1_Pmig2-6Ros1 x FB2Δros1_Pmig2-6Ros1. B and D panels show confocal microscopy pictures obtained from 3 dpi plant samples. The fungal cell wall was stained with wheat germ agglutinin-Alexa Fluor 488 (green fluorescence) and the plant cell wall was stained with propidium iodide (red fluorescence). Growth of the strains expressing ros1 prematurely is restricted to a small area surrounding the penetration site and hyphae exhibit an altered morphology. The inserts depict enlargements of biotrophic hyphae displaying increased septation when Ros1 is prematurely expressed. Bar = 10 μm.