Transcriptional Analysis of Genes Encoding Functional delta9- and delta12-Acyl Lipid Desaturases in Relation to the Production of gamma-Linolenic Acid in Mutants of Spirulina platensis

Name: Sakunda Anggarini

keyword: Spirulina platensis

Abstract: Spirulina platensis strain C1 (wild type, WT) and its mutant strains defective in gamma- linolenic acid (GLA, C18:3 delta6, 9, 12) production, namely I18, I22, I30 and I30/1, have been characterized. In this study, stability of morphological characteristics and fatty acid profile of the mutants were reconfirmed. Molecular characteristics of desC and desA of the mutants were characterized, in addition to previous study (Chamutpong, 2000) of transcriptional characteristics of desD. Nucleotide sequences analysis of both genes desC and desA in all mutant strains showed normal, in comparison to that of the WT. The mutant strain I18, levels of fatty acids, oleic- and linoleic acids, were well correlated with the gene expression of desC and desA, and harmoniously to their mRNA half-life, respectively. The evidences, including the desD mRNA level that was consistent with changing in fatty acids ratio, suggested that regulation of unsaturated fatty acids C18 in this strain were controlled at transcription level. In the mutant I30 and I30/1 cultures grown at optimal or lower temperature, proportions of most of C18 fatty acids were not significantly altered. The mutant I30, although production of oleic acid (C18:1 delta9) was only 78 %, mRNA level of the desC and its half-life were alike to those of the WT, indicated that this gene expression controlling was normal, but not the enzyme activity. However, desA mRNA in this mutant was also resembling, whereas its half-life (14.5 minutes) was significant longer than that of the WT (11 minutes). Similarly, the linoleic acid (C18:2 delta9,12) production was 135 % of the WT, demonstrated that the expression of desA in this mutant was controlled by both mRNA synthesis and mRNA stability. The evidences, in addition to transcriptional regulation of desD (Chamutpong, 2000), suggested that the regulation of unsaturated fatty acids C18 in this I30 mutant were controlled at transcription level even though defective in enzyme activity or post-transcription such as mRNA stability of earlier steps might be the matter. Unlike the I30, the mutant I30/1, which the truncated protein of the desD expression led to a loss activity of GLA synthesis (Chamutpong, 2000), the desC mRNA level was consistent with the level of oleic acid, its half-life was much significant shorter (16.5) than that of the WT. While, desA mRNA level and its half-life were comparable with that of the WT, the linoleic acid production was double level. This was due to non-extension of the acid as a substrate of GLA synthesis or enzymatic activity defect of the desD, though its desC and desA mRNA levels were comparable with that of the WT. For the mutants I22, desC mRNA level was similar, its mRNA half-life showed shorter, 18.5 minutes compared to 22 minutes of the WT, corresponding to the half level of oleic acid. Moreover, desA gene showed interesting expression with the highest level (1.4X) compared to other strains including the WT. It was supported by the mRNA stability (half-life of 19 min) of this strain versus that of the WT (11 min), indicated that the desA gene expression in the mutant I22 was controlled at post-transcription level. These evidences, besides its defective in photosynthesis and exhibited high stability of the desD mRNA (Ruengjitchatchawalya et al., 2002; Chamutpong, 2000), the desaturation of fatty acid C18 in this I22 mutant was controlled at post-transcription level, particularly in relation to the enzyme activities.

King Mongkut's University of Technology Thonburi. KMUTT Library

Address: BANGKOK

Email: info.lib@mail.kmutt.ac.th

Name: Marasri Ruengjitchatchawalya

Role: Advisor

Created: 2008

Modified: 2011-06-08

Issued: 2011-06-07

วิทยานิพนธ์/Thesis

application/pdf

CallNumber: BIT625

eng

DegreeName: Master of Science

Level: Master's Degree

Descipline: Biotechnology

Grantor: King Mongkut's University of Technology Thonburi

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