Conidial germination in Aspergillus nidulans requires RAS signaling and protein synthesis

The dormant spores of Aspergillus nidulans become competent for growth and nuclear division in a process called conidial germination. To analyze the m olecular details of conidial germination, we developed a genetic screen in which we identified spore germination-deficient mutants that are blocked in this process at the restrictive temperature. These mutants defined eight g enes, of which we identified five. Four of the five were directly involved in translation and protein folding, and the fifth showed a high degree of h omology to a malonyl CoA synthetase. These results suggest that out of a wi de array of processes occurring during conidial germination, translation is essential if germination is to proceed. We also show that conidia containi ng a mutant-activated form of rasA, the ras homologue in A. nidulans, germi nate in the absence of an inducing carbon source, suggesting an important r ole for rasA signaling in conidial germination. Together these data suggest a model by which a carbon source activates a ras-independent sensory mecha nism, inducing translation and leading to conidial germination. This study shows that conidial germination in A. nidulans requires protein synthesis a nd that the initiation of translation is linked, through an as yet to be de termined signaling cascade that includes rasA, to a carbon-source-sensing a pparatus.