Genetics and Genomics of Sexual Development of Aspergillus nidulans
Kap-Hoon Han and Dong-Min Han
from: Aspergillus: Molecular Biology and Genomics (Edited by: Masayuki Machida and Katsuya Gomi). Caister Academic Press, U.K. (2010)
About half of Aspergilli species that belongs to ascomycetes are known to have sexuality and most of them are homothallic. A number of cleistothecia are formed in a thallus grown from a single haploid conidia or ascospores. Asci develop within a cleistothecium and eight ascospores are produced in an ascus as a result of meiosis followed by an additional mitosis. Genome-sequencing project revealed that two mating genes (MAT) encoding the regulatory proteins that are necessary for controlling partner recognition in out-cross species of filamentous fungi were conserved in most Aspergilli species. The MAT gene products in some self-fertile species were not required for recognition of mating partner at pheromone-signaling stage but required at later stages of sexual development. Various environmental factors such as nutritional status, culture conditions and several stresses, influence the decision or progression of sexual reproduction of self-fertile Aspergilli. A large number of genes are expected to be involved in sexual development of A. nidulans which can be grouped into several categories according to the development stages, such as the decision of sexual reproductive cycle, mating process, growth of fruiting body, karyogamy followed by meiosis and sporulation process. Complicated regulatory networks including signal transduction pathways and gene expression control may work in each stage and stage to stage linkages. In this chapter, we briefly reviewed the components joining in the regulatory pathways of sexual development, although they comprise only a small part of the whole regulatory networks. Most of the genes characterized act in the reproduction decision stage or early sexual development. Some of them control sexual development positively and some negatively. Several components in signal transduction pathways and protein kinases play some roles in decision of sexual development or in formation of fruiting bodies, although the information on the signal they response to and on the transcription factors they connect with is very poor. Regarding the difficulties for studying sexual differentiation, recent progresses in genomics of Aspergilli enlarge the boundaries of genetic and molecular biological understanding of sexual development even in the non-fertile species read more ...