A Neurospora Mutant with Abnormal Croziers, Giant Ascospores, And Asci Having Multiple Apical Pores

ABSTRACT

A dominant mutant of Neurospora crassa named Perforated (Prf) resembles giant spore (gsp) in making giant ascospores, and resembles Banana (Ban) in making giant ascospores and abnormal croziers. In Ban and Prf, the first-formed croziers appear normal and differentiate asci, but the later-formed croziers revert to mitosis and become multinucleate. In addition, Prf shows a unique developmental phenotype not found in gsp or Ban: nearly all asci form multiple pores at their apices so as to resemble salt shakers. When mature giant ascospores are expelled from Prf asci, the ascus apex is ruptured. In addition to its dominant effects on ascus development, Prf acts as a recessive lethal in the vegetative phase and can only be maintained in a (Prf + Prf+) heterokaryon. Attempts to obtain homokaryotic Prf cultures from the heterokaryon by conidial isolation were not successful, nor could Prf be recovered from the infrequent normal-sized ascospores. Prf was mapped by analyzing normal-sized ascospores from a cross of a multiply-marked linkage tester of mating type a fertilized with conidia of a (Prf A + Prf + a^m33) heterokaryon and noting which marker segregation deviated from a 1:1 ratio. A subsequent four-point cross confirmed that Prf is located right of al-3 (3% recombination) in linkage group VR.

Key Words:

• Neurospora crassa
• ascus development
• giant ascospores
• crozier abnormality
• recessive lethal mutation