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Many developmental mutants blocked prior to activation of brlA expression were subsequently found. These mutants are described as "fluffy"—they form white, cotton-like aerial hyphae that do not conidiate. These mutants, fluA, fluB, fluC, fluD, fluE and fluG, conidiate when grown on minimal media or when grown in contact with wild colonies, suggesting a signaling molecule is involved in the differentiation of the conidiophore. The signaling molecule can work if the two strains are separated by a dialysis membrane with a 6000 to 8000 dalton pore size, suggesting that it is a low-molecular weight, diffusible compound. The fluG (also known as acoD) mutant is deficient in the production of a conidiation signal. It is thought that fluG participates early, prior to brlA in programmed developmental induction pathway (Adams et al., 1998).

Developmental timeline

Induction Vesicle Metulae and phialide Spore formation formation formation and maturation fluG flbA-E

Class C and D 'Middle'

brlA

Class C and D 'Middle'

brlA

Class A 'early'

Class B 'Late'

Figure 7.5 Interactions among the regulatory genes during conidiophore development in Aspergillus nidulans. (From Adams (1995).)

Class A 'early'

Class B 'Late'

Figure 7.5 Interactions among the regulatory genes during conidiophore development in Aspergillus nidulans. (From Adams (1995).)

The work reviewed above shows that the potential of A. nidulans is being realized in identifying the key genes that regulate the switch from vegetative growth to the initiation of development that involves hundreds of other genes for the formation of asexual spores.

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