Differential expression of desaturases and changes in fatty acid composition during sporangiospore germination and development in Mucor rouxii

Abstract

Polyunsaturated fatty acids (PUFAs), namely, oleic (C18:1), linoleic (C18:2), and γ-linolenic acid (C18:3), constituted the majority in the total fatty acid content (44%) of sporangiospores of Mucor rouxii. At 30 °C, the germination begins within 1 h at which time spore swelling occurs, followed by germ tube emergence within 3–4 h. Throughout germination, an increase in γ-linolenic acid (GLA) was observed and its content was highest at germ tube emergence. It took longer for sporangiospores of M. rouxii to germinate at sub-optimal temperatures (15 and 35 °C). However, the content of GLA was higher at the germ tube initiation than at the mycelial stage at all temperatures, suggesting the association of GLA and germination of sporangiospores. This finding was substantially confirmed by differential expression of Δ 9-, Δ 12-, and Δ 6-desaturase genes measured during spore germination. The expression of three desaturase genes parallels the pattern of GLA synthesis. By using RT-PCR techniques to follow gene expression, we found that mRNA of Δ 12- and Δ 6-desaturase genes were translated as soon as the spores were introduced into a fresh medium while the mRNA of Δ 9-desaturase gene could not be detected until 2 h after introduction. A sharp increase in mRNA of Δ 6-desaturase genes correlated well with an increase in GLA content at germ tube emergence (4 h). These results demonstrated that changes in fatty acid composition of sporangiospore of M. rouxii and differential expression of desaturase genes occurred during germination, and that extensive changes in GLA synthesis associated with some events in germination process.