Examination of the relationship between asexual development and sterigmatocystin production in Aspergillus nidulans /
The fungal secondary metabolites, sterigmatocystin (ST) and aflatoxin (AF), produced by Aspergillus species, are the most toxic, carcinogenic and mutagenic compounds found in nature. These toxins pose significant health and economic risks due to their presence in agricultural crops. ST biosynthesis...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1999.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=731686311&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The fungal secondary metabolites, sterigmatocystin (ST) and aflatoxin (AF), produced by Aspergillus species, are the most toxic, carcinogenic and mutagenic compounds found in nature. These toxins pose significant health and economic risks due to their presence in agricultural crops. ST biosynthesis in the fungus Aspergillus nidulans is accomplished by activation of 26 genes (etc genes) found in a cluster. An analogous gene cluster is found in Aspergillus flavus and Aspergillus parasiticus.. These genes (both stc and AF) are regulated by the positively-acting transcriptional factor, Af1R. I examined the genetic relationship between the regulation of asexual reproduction (conidiation) and ST production in Aspergillus nidulans. This research details the discovery that ST production and conidiation are regulated through a, proliferative growth-activating signal transduction pathway mediated by the α-subunit of a heterotrimeric G-protein, FadA. Furthermore, I discuss a mutagenesis designed to identify genes that lie in this FadA-mediated signal transduction pathway leading to af1R expression. The strain that I mutagenized had mutations in a developmental gene that disallowed both conidiation and ST production as well as a mutation, which allowed me to visualize whether the ST biosynthesis pathway was activated. I then looked for mutants, which were able to activate the ST biosynthesis pathway inspire of the developmental gene mutation. Nine mutants were isolated, 1 of which had a mutation linked to the ST biosynthetic cluster. Neither the number of mutated genes represented in the 9 mutants nor the dominant/recessive nature of the mutations was able to be determined. Finally, the isolation and characterization of a gene, rcoA is described. Because the product of the rcoA homolog in Neurospora crassa, RCO-I, regulates conidiation, I hypothesized that RcoA may have a similar role and in addition may regulate ST production. rcoA is constructively expressed in a wild-type stain, producing a transcript of approximately 2.5 kb. Deletion of the rcoA gene causes a severe growth and speculation defect and loss of ST production and stc gene expression. In addition, the transcription of an early acting developmental gene, brlA, is affected in a rcoA deletion strain. |
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| Item Description: | Vita. "Major Subject: Plant Pathology". |
| Physical Description: | x, 99 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 86-96). |