Pearls Comparative Genomics of Plant Fungal Pathogens: The Ustilago-Sporisorium Paradigm

The closely related smut fungi Ustilago maydis, U. hordei, and Sporisorium reilianum f. sp. zeae are facultatively biotrophic basidio-mycetes that occur ubiquitously. Teliospores germinate to produce sporidia of different mating type that grow saprophytically and multiply mitotically by budding [1]. For mass proliferation and sexual genetic exchange, successful colonization of economically important crop plants like maize, barley, and oats is a prerequisite. Mating of compatible haploid yeast cells leads to the formation of dikaryotic filaments that are infection competent. These filaments enter their hosts by penetration of the leaf surface [2]. Once inside the plant, filaments multiply in the affected tissue and induce spore formation in tumors near the penetration site (U. maydis) [3] or spread through the entire plant and form spores in inflorescences (S. reilianum and U. hordei) [4,5]. Although presence of the fungus is clearly detected [6], defense reactions of native host plants are ver