Transcriptional profiling reveals differentially expressed genes involved in lipid biosynthesis during cacao seed development

Abstract

Theobroma cacao is a plant of economic value due to the use of its seed lipid for chocolate, confectionery, and cosmetic industries. The seed lipid contains a stable ratio of saturated and unsaturated fatty acids, which determines its unique melting temperature. However, little is known about the molecular mechanism determining the fatty acid ratio and lipid content in cacao. To gain insight into the unique properties of lipid synthesis in cacao, biochemical and transcriptomic approaches were used to compare the lipid accumulation between high and low lipid content cacao accessions. Lipid accumulation rates and lipid content were different between the two accessions. Moreover, differentially expressed genes were detected between high and low lipid content cacao accessions. The data allowed the identification of distinct candidate genes and furthered our understanding of lipid accumulation, potentially explaining the differences in lipid content between various cacao accessions. The results might be used to develop molecular tools and engineer alternative pathways for cacao breeding with improved lipid production potentials.

Figure 1

Pods of Theobroma cacao L. TAS42 and TAS57 used in transcriptional sequencing. (a–d) TAS42 pods at 105, 126, 147, and 168 DAP, respectively. (e–h) TAS57 pods at 105, 126, 147, and 168 DAP, respectively. (i–l) TAS42 seeds at 105, 126, 147, and 168 DAP, respectively. (m–p) TAS57 seeds at 105, 126, 147, and 168 DAP, respectively.

Figure 2

Changes in the lipid content and fatty acid composition of TAS42 and TAS57 during pod development. (a) Patterns of lipid accumulation in the developing seed. (b) Changes in fatty acid composition of the TAS42 seed during pod development. (c) Changes in fatty acid composition of the TAS57 seed during pod development. Values are the means of three biological replicates. C12:0, lauric acid; C16:0, palmitic acid; C18:0, stearic acid; C18:1, oleic acid; C18:2, linoleic acid; C18:3, alpha-linolenic acid; C20:0, arachidic acid; C22:0, behenic acid.

Figure 3

Transcripts differentially expressed between different seed developmental stages. Up- and downregulated transcripts were quantified. The results of ten comparisons between the two accessions are shown.

Figure 4

Venn diagram of DEGs in different seed developmental stages. (a) Distribution of DEGs in different seed developmental stages between accessions TAS42 and TAS57, (b) Distribution of DEGs in different seed developmental stages of accession TAS42, (c) Distribution of DEGs in different seed developmental stages of accession TAS57.

Figure 5

Expression analysis of 15 candidate DEGs related to lipid biosynthesis metabolism in the cacao seed by qRT-PCR. The Y-axis represents the relative expression, and the X-axis depicts the pod maturation stages. The experiment was repeated three times, and the resulting data are presented with error bars, with n = 3.