Identification of differentially expressed genes in the commercially important agarophyte, Gracilaria gracilis, following nitrogen deprivation

Master Thesis


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University of Cape Town

The red agarophytic alga, Gracilaria gracilis, occurs naturally within Saldahna Bay, South Africa. Gracilaria species are commercially exploited for their hydrocolloid agar, valued at US$132 million per annum (FAO, 2002). G. gracilis is thus a valuable resource for South Africa in terms of generating foreign currency through export. Nitrogen limitation occurring within Saldahna Bay during the summer to autumn months, however, is considered to be the major factor preventing commercial cultivation of G. gracilis. Algae possess various survival mechanisms that generally involve the activation or repression of various gene regulatory systems. Such regulatory systems aid in preserving energetic homeostasis at a cellular level, thereby allowing maximal algal survival during adverse environmental conditions. Microarray technology is a highthroughput global gene analysis tool, allowing for the simultaneous identification of thousands of differentially expressed genes in a single assay. Combined with genomic technologies such as genetic engineering, microarray technology has the potential to identify genes that confer enhanced in vivo tolerance to a specific stress. In the current investigation, microarray technology was utilized to identify genes differentially expressed in G. gracilis in response to nitrogen limitation. A total of 39 differentially expressed genes were identified. Ofthe 35 genes that were sequenced, 13 were assigned a putative function based on sequence similarity to genes deposited in various databases. The remaining sequences corresponded to either unknown hypothetical proteins or else had no significant homology to any of the sequences in the databases. Overall, the current investigation has provided a foundation for future research into the biological role(s) of each of the identified differentially expressed genes within their true isogenic background. Future studies may thus allow for improved crop tolerance and stability, enhancing aquaculture of this valuable resource in Southern Africa.

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