Infection structures from rust urediospores: effect of RNA and protein synthesis inhibitors

Isolation of genes expressed during compatible interactions between leaf rust (Puccinia triticina) and wheat using cDNA-AFLP

SUMMARY The rust fungi are obligate biotrophic pathogens that depend on living host tissue for their growth. In compatible interactions they go through a number of developmental stages to form intercellular hyphae and haustoria within host cells, through which they obtain their nutrients. Here we have exploited the cDNA-AFLP technique to isolate fragments of wheat and rust genes that are expressed at specific defined time-points during the infection process. A number of these sequences were used as probes in Northern hybridizations and in RT-PCR to confirm their expression patterns, and were also characterized by PCR analysis and Southern hybridizations to determine whether they are of fungal or wheat origin. A cDNA library was constructed from pooled RNAs extracted from days 5 and 7 after inoculation, and this library was screened to isolate full-length cDNAs of selected sequences. Sequence analysis of these cDNA fragments and clones revealed similarities amongst the fungal genes to a chitinase, a sorbitol utilization protein, an arabinitol dehydrogenase and a proteasome regulatory unit, whilst in wheat, we identified sequences with homology to a katanin and a cell enlargement protein.

Properties of polyadenylate-associated ribonucleic acid from Saccharomyces cerevisiae ascospores

Bulk ribonucleic acid (RNA) was isolated from mechanically disrupted ascospores of Saccharomyces cerevisiae. After two passes over an oligo (dT10) cellulose column, the portion which bound, called poly(A)(+), was characterized. It is heterodisperse in size with a mean molecular weight of approximately 4 X 10(5), but contains some species as large as 7 X 10(5). The base composition is similar to vegetative poly(A)(+) RNA. The polyadenylate segment is also heterogenous in size, ranging from 90 to 20 bases in length, with a peak at approximately 60 nucleotides in length. Pulse-labeling of asci with [3H-methyl]methionine yields two "caps," 7-methyl guanosine-5'-triphosphoryl-5'-adenosine (or guanosine) identical to that found in vegetative poly(A)(+) RNA. The poly(A)(+) RNA in spores is found in polyribosomes which are, on the average, smaller than vegetative ones. Long-term labeling studies indicate that the fraction of poly(A)(+) RNA in spores is similar to that in vegetative cells.

Acrolein Induces Differentiation of Infection Structures in the Wheat Stem Rust Fungus

A chemical factor from wheat stem rust uredospores that induces infection structure formation has been identified as acrolein (2-propenal). This compound is the active component of distillates from uredospore extracts previously shown to induce infection structure formation.