Chapter 27 Genetic and Cell Cycle Analysis of a Smut Fungus (Ustilago violacea)

Siderophore accumulation and phytopathogenicity in Microbotryum violaceum

“…The most obvious explanation of this phenomenon is the recovery of products from two or more germinated teliospores, which might result from clumping of teliospores during the plating procedure. This had not been an apparent problem in previous analyses, and its occurrence was estimated by Cummins and Day (1977) using the same technique at <0.5%. However, other researchers using the same technique of teliospore germination and recovery of products in M. violaceum have typically examined only two, rather than three loci, therefore recovery of more than four products would be undetectable.…”

The distribution of mating-type bias in natural populations of the anther-smutUstilago violaceaonSilene albain Virginia

“…Instead, all our evidence is consistent with the presence of a haplolethal deficiency linked to mating type; by this mechanism, we can explain the recovery of only the Al mating type in sporidial lines and the failure of such lines to transmit the bias. In the context of the classical view of the life-cycle of U. violacea (Cummins and Day, 1977) where conjugation and infection follows a period of sporidial multiplication, the haplolethal allele would obviously be severely disadvantaged, since the A2 sporidia could not grow and mate. However, this does not appear to be the case, as we found no evidence that the frequency of bias is associated with a decreased disease incidence or slower rates of disease spread.…”

“…This promycelium is usually three-celled and each promycelial cell and the teliospore itself then buds off one or more sporidia, which multiply mitotically by budding. These sporidia are of two mating types, Al and A2, which conjugate to form an infective dikaryotic hypha that invades and eventually spreads throughout the host plant (Cummins and Day, 1977). When an infected plant flowers, the mycelium enters the developing anthers, undergoes karyogamy, and differentiates to produce large numbers of diploid teliospores (Batcho and Audran, 1980).…”

“…comm.). This phenomenon is particularly interesting because it has generally been con-sidered that fusion of opposite mating types is a prerequisite for dikaryon formation and infectivity of U. violacea (Cummins and Day, 1977) and of most other smut fungi (Fischer and Holton, 1957); the absence of sporidia of one mating type might be expected to have severe consequences for fungal pathogenicity. Similar deficiencies of sporidia of one mating type have been observed in other Ustilaginales (Holton, 1951;Grasso, 1955), and have been explained as the result of mutations which result in loss of viability in the haploid phase ("haplolethal deficiencies") but which may have compensatory advantages in the diploid pathogenic phase.…”

Genomic and transcriptomic analyses of Microbotryum lychnidis-dioicae provide insights into the biology of a fascinating fungal phytopathogen.

“…The deposited teliospores germinate and undergo meiosis, leading to a linear tetrad that produces haploid yeast-like sporidia of opposite mating types, a 1 and a 2 (Garber & Day, 1985), analogous to gametes of the fungus. Conjugation between sporidia of opposite mating types is required to initiate the growth of dikaryotic infectious hyphae (Cummins & Day, 1977), which "travel" through the intercellular spaces of the apical meristem of infected plants where they reside and subsequently infect the plant systematically. However, the exact location and mechanism of infection is still unclear (Schäfer et al, 2010).…”