Effect of surface wettability on germination and gene expression in Cronartium quercuum f. sp. fusiforme basidiospores

Abstract

Cronartium quercuum f. sp . fusiforme is an obligate pathogen of pine and oak. Its basidiospores are specifically adapted to recognize and establish infections on the pine host. Depending on environmental cues, the basidiospores can germinate directly, which typically leads to infection of pine, or indirectly, which usually results in formation of secondary basidiospores. We investigated how changes in surface wettability, or hydrophilicity, affect basidiospore germination. When we decreased surface wettability, the direct germination and total germination (direct+indirect) frequencies increased. Additionally, there was a critical threshold between 42% and 54% wettability, at which the basidiospores switched from direct to indirect germination. We conclude that the germination type of C. q. fusiforme basidiospores is influenced by the hydrophilicity of the surface upon which they land. To gain insight into gene expression during basidiospore germination, we made two suppression subtraction hybridization (SSH) libraries enriched for genes expressed during each type of germination. A total of 172 unique gene sequences were recovered from the two expression libraries. Annotation of these libraries indicates that they include several clones that may encode rust-specific or basidiomycete-specific functions.