Fig. 1

Primary hypha differentiates bulbous growth prior to mitosis. a Schematic diagram of IH development inside rice cells (rectangles), seen from above. Left (22–26 h post inoculation; hpi): A filamentous primary hypha (white), derived from the appressorium (gray circle) on the rice cell surface, grows inside the rice cell. The hyphal apex is associated with the tip BIC (red). Middle (26–28 hpi): The primary hypha differentiates into bulbous IH, and the tip BIC becomes the side BIC (red). Right (36–40 hpi): IH have filled the first invaded rice cell, and IH with secondary BICs are growing into a neighboring cell. b Hyphal development of M. oryzae CKF2138 in YT16 rice sheath cells at 26–27 hpi. Shown are maximum intensity projections of confocal optical sections (14–53 μm in total depth). Merged fluorescence shows fungal cytoplasmic EYFP (green) and nuclear tdTomato (red, but shown in yellow or orange due to the overlap of green and red). Top: The appressorium (asterisk) contained one nucleus (arrowhead) and produced an anucleate filamentous primary hypha at 26 hpi. Middle: The tip of the primary hypha swelled but remained anucleate at 27 hpi. Bottom: The bulbous end of the primary hypha had become nucleated at 27 hpi. Arrows indicate the apical region of the primary hypha which correlates with the hyphal diameter measurements in (c). Bar = 5 μm. c Graph showing measurements of the diameter at the apical region of the primary hypha, corresponding to the location of arrows in (b). Groups of infection sites were plotted on the y-axis in 1 μm hyphal diameter increments and the x-axis shows number of infection sites (n = 124). Anucleate hypha and nucleated hypha are differentiated by blue and red bars, respectively