Abstract
BackgroundNeocinnamomum caudatum (Nees) Merr., a biodiesel tree species in the subtropical areas of South China, India and Burma, is distinctive from other species in Lauraceae family and its seed oil is rich in linoleic acid (18:2) and stearic acid (18:0). However, there is little genetic information about this species so far. In this study, a transcriptomic analysis on developing seeds of N. caudatum was conducted in an attempt to discern the molecular mechanisms involving the control of the fatty acid (FA) and triacylglycerol (TAG) biosynthesis.ResultsTranscriptome analysis revealed 239,703 unigenes with an average length of 436 bp and 137 putative biomarkers that are related to FA formation and TAG biosynthesis. The expression patterns of genes encoding β-ketoacyl-acyl carrier protein synthase I (KASI), β- ketoacyl-acyl carrier protein synthase II (KASII), stearoyl-ACP desaturase (SAD), fatty acid desaturase 2 (FAD2), fatty acid desaturase 8 (FAD8) and acyl-ACP thioesterase A/B (FATA/B) were further validated by qRT-PCR. These genes displayed a very similar expression pattern in two distinct assays. Moreover, sequence analysis of different FATBs from diverse plant species revealed that NcFATB is structurally different from its counterpart in other species in producing medium-chain saturated FAs. Concertedly, heterologous expression of NcFATB in E. coli BL21 (DE3) strain showed that this corresponding expressed protein, NcFATB, prefers long-chain saturated fatty acyl-ACP over medium-chain fatty acyl-ACP as substrate.ConclusionsTranscriptome analysis of developing N. caudatum seeds revealed a composite molecular map linked to the FA formation and oil biosynthesis in this biodiesel tree species. The substrate preference of NcFATB for long-chain saturated FAs is likely to contribute to its unique seed oil profile rich in stearic acid. Our findings demonstrate that in the tree species of Lauraceae family, the FATB enzymes producing long-chain FAs are structurally distinct from those producing medium-chain FAs, thereby suggesting that the FATB genes may serve as a biomarker for the classification of tree species of Lauraceae family.
Highlights
Neocinnamomum caudatum (Nees) Merr., a biodiesel tree species in the subtropical areas of South China, India and Burma, is distinctive from other species in Lauraceae family and its seed oil is rich in linoleic acid (18:2) and stearic acid (18:0)
Americana and N. caudatum, seed oil content reaches more than 25% on the dry weight basis versus less than 5% in M. yunnanensis, P. cavaleriei and C. tonkinensis
We found that heterologous expression of NcFATB in E. coli BL21 (DE3) cells resulted in a 2.86-fold increase in total free Fatty acids (FAs)
Summary
Neocinnamomum caudatum (Nees) Merr., a biodiesel tree species in the subtropical areas of South China, India and Burma, is distinctive from other species in Lauraceae family and its seed oil is rich in linoleic acid (18:2) and stearic acid (18:0). Palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2) and linolenic acid (18:3), respectively account for 11.3, 21.2, 15.8, 35 and 13.1% of the total FAs (expressed as a mole percent) [6, 7] Such a high proportion of 18:0 is rare in the family Lauraceae and even in the subclass Magnoliidae, implying that the molecular mechanisms governing the FA formation and triacylglycerol biosynthesis in seeds of N. caudatum are very likely to be different from those in other well-documented species in the family Lauraceae. Little is known about its genomic information so far
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