Stored mRNA in sporangiospores of the fungus Mucor racemosus

Abstract

When introduced into nutrient medium under air, the asexual sporangiospores of Mucor racemosus germinated within 5 to 8 h, culminating with the emergence of germ tubes. We found that sporangiospores increased 20%/o in dry weight during the first 60 min of germination, indicating a high degree of synthetic activity. Sucrose density gradient analysis of spore extracts revealed that the percentage of ribosomes associated with mRNA increased from 22.5% in dormant spores to 85% within 10 min after the addition of medium and remained at this level for at least 3 h. L-[14CJleucine was immediately incorporated at a rapid rate into protein of a leucine auxotroph, whereas [3H]uracil or [32Plphosphate was incorporated into RNA at a significant rate only 20 min after the addition of medium. This newly synthesized RNA occurred in polysomes only after 30 min had passed. Pool equilibration of the radioactive precursors was not limiting to these measurements. Polyadenylated RNA was isolated from dormant spores by oligodeoxythymidylic acid-cellulose chromatography and was found to comprise 3.3% of the total cellular RNA. Sucrose density gradient centrifugation revealed the polyadenylated RNA to be heterodisperse in size, ranging from 6S to 20S. It was concluded that M. racemosus sporangiospores contain preformed mRNA which is translated commencing immediately upon the addition of nutrient medium.

Quantification of ToxB gene expression and formation of appressoria by isolates of Pyrenophora tritici‐repentis differing in pathogenicity

“…A number of fungal species, such as Botryodiplodia theobromae (Knight et al ., 1976), Mucor racemosus (Linz et al ., 1982) and Neurospora tetrasperma (Plesofsky‐Vig et al ., 1992), are known to produce stored mRNA that is translated upon germination. Given the importance of Ptr ToxB in establishing a compatible interaction between host and pathogen, its presence in conidia presumably enables faster toxin production during the early stages of infection.…”

β‐1,3‐Glucanase gene expression in low‐hydrated seeds as a mechanism for dormancy release during tobacco after‐ripening

“…, 1989) and ciliates (Gutiérrez et al. , 2001), and spores of fungi (Linz and Orlowski, 1982) and other microbes (Potts, 1994). Transcripts stored in air‐dry seeds are also transiently translated very early during imbibition (Bewley, 1997b; Comai and Harada, 1990; Leubner‐Metzger et al.…”

Differential gene expression during aerobic germination of Mucor racemosus sporangiospores

“…When placed ihto a hexose-containing nutrient medium under CO2 or N2, for example, the sporangiospore carries out an essentially equivalent amount of spherical growth before initiating the formation of multipolar buds. Several previous studies have dealt with the aerobic germination of Mucor sporangiospores (13,18,19,21,(27)(28)(29)33), and this is the system of development we have focused upon in the present work.…”

“…We have previously shown that M. racemosus sporangiospores contain a sizable pool of stored mRNA which is translated immediately upon the initiation of germination. Proteins synthesized during the first 30 min of germination are translated only from the stored mRNA (13). In the present study, we compared the proteins synthesized in vivo from the stored mRNA during early germination with the proteins accumulated in vivo during spore formation by means of sodium dodecyl sulfate (SDS)-polyacrylamide slab gel electrophoresis and two-dimensional isoelectric focusing-St)S-polyacrylamide gel electrophoresis.…”