Signaling for Growth Orientation and Cell Differentiation by Surface Topography in <i>Uromyces</i>

TLDR

The study used electron‑beam lithography to microfabricate silicon ridges of defined dimensions to probe how topographical cues guide growth orientation and infection structure formation in *Uromyces appendiculatus*. The fungus responds most strongly to a 0.5‑µm‑high ridge, with effective orientation occurring for ridge spacings of 0.5–6.7 µm, while elevations outside 0.25–1.0 µm are ineffective, indicating the pathogen can detect subtle topographic variations.

Abstract

The dimensions of the topographical signals for growth orientation and infection structure formation, a cell differentiation event that includes nuclear division, were determined for the stomatal penetrating rust fungus Uromyces appendiculatus. The differentiation signal was found to be a simple ridge on the substrate surface that had a markedly optimum height of 0.5 micrometer. Such ridges were microfabricated on silicon wafers by using electron-beam lithography. A similar ridge, in the form of a stomatal lip, was found associated with the stomatal guard cells of the bean (Phaseolus vulgaris) leaf. Ridge elevations greater than 1.0 micrometer or less than 0.25 micrometer did not serve as effective signals. Germ tubes of the fungus were highly oriented by ridge spacings of 0.5 to 6.7 micrometers. The data indicate that the fungus is able to distinguish uniquely minute differences in leaf surface topography in order to infect the host plant.