Date Published: August 16, 2019
Publisher: Public Library of Science
Author(s): Hiroki Kawamoto, Kaori Yamanaka, Ayako Koizumi, Kotaro Ishii, Yusuke Kazama, Tomoko Abe, Shigeyuki Kawano, Hiroshi Ezura.
Silene latifolia is a dioecious flowering plant with sex chromosomes in the family Caryophyllaceae. Development of a gynoecium and stamens are suppressed in the male and female flowers of S. latifolia, respectively. Microbotryum lychnidis-dioicae promotes stamen development when it infects the female flower. If suppression of the stamen and gynoecium development is regulated by the same mechanism, suppression of gynoecium and stamen development is released simultaneously with the infection by M. lychnidis-dioicae. To assess this hypothesis, an asexual mutant without a gynoecium or stamen was infected with M. lychnidis-dioicae. A filament of the stamen in the infected asexual mutant was elongated at stages 11 and 12 of flower bud development as well as in the male, but the gynoecium did not form. Instead of the gynoecium, a filamentous structure was suppressed as in the male flower. Developmental suppression of the stamen was released by M. lychnidis-dioicae, but that of gynoecium development was not released. M. lychnidis-dioicae would have a function similar to stamen-promoting factor (SPF), since the elongation of the stamen that is not observed in the healthy asexual mutant was observed after stage 8 of flower bud development. An infection experiment also revealed that a deletion on the Y chromosome of the asexual mutant eliminated genes for maturation of tapetal cells because the tapetal cells did not mature in the asexual mutant infected with M. lychnidis-dioicae.
The basidiomycetous genus Microbotryum is a species-rich member of smut fungi that infect a wide range of host plants belonging to the dicotyledonous families Caryophyllaceae, Dipsacaceae, Lamiaceae, and Lentibulariaceae . The smut fungus Microbotryum lychnidis-dioicae was isolated from Silene latifolia . M. lychnidis-dioicae has long been used as a model for studying the ecology, genetics, and the propagation of sexual infection [3–5]. Smut disease is transmitted by smut spores attached to insects . Spore germination, meiosis, and the mating of paired basidiospores of smut fungi occurs on the host cell surface . The basidiospores of smut fungi form a dikaryotic mycelium after mating, which penetrates the host plant. The dikaryotic mycelium of smut fungi is observed in intercellular regions, vascular bundles, and apical meristem after invasion of the host plant. Subsequently, the dikaryotic mycelium of smut fungi forms smut spores in the pollen sacs in the blossoms of host plants .