Abstract
BackgroundPods of the vanilla orchid (Vanilla planifolia) accumulate large amounts of the flavor compound vanillin (3-methoxy, 4-hydroxy-benzaldehyde) as a glucoside during the later stages of their development. At earlier stages, the developing seeds within the pod synthesize a novel lignin polymer, catechyl (C) lignin, in their coats. Genomic resources for determining the biosynthetic routes to these compounds and other flavor components in V. planifolia are currently limited.ResultsUsing next-generation sequencing technologies, we have generated very large gene sequence datasets from vanilla pods at different times of development, and representing different tissue types, including the seeds, hairs, placental and mesocarp tissues. This developmental series was chosen as being the most informative for interrogation of pathways of vanillin and C-lignin biosynthesis in the pod and seed, respectively. The combined 454/Illumina RNA-seq platforms provide both deep sequence coverage and high quality de novo transcriptome assembly for this non-model crop species.ConclusionsThe annotated sequence data provide a foundation for understanding multiple aspects of the biochemistry and development of the vanilla bean, as exemplified by the identification of candidate genes involved in lignin biosynthesis. Our transcriptome data indicate that C-lignin formation in the seed coat involves coordinate expression of monolignol biosynthetic genes with the exception of those encoding the caffeoyl coenzyme A 3-O-methyltransferase for conversion of caffeoyl to feruloyl moieties. This database provides a general resource for further studies on this important flavor species.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-964) contains supplementary material, which is available to authorized users.
Highlights
Pods of the vanilla orchid (Vanilla planifolia) accumulate large amounts of the flavor compound vanillin (3-methoxy, 4-hydroxy-benzaldehyde) as a glucoside during the later stages of their development
The annotated sequence data provide a foundation for understanding multiple aspects of the biochemistry and development of the vanilla bean, as exemplified by the identification of candidate genes involved in lignin biosynthesis and interrogation of their expression patterns in the developing pod and seed in relation to the accumulation of the C-lignin polymer in the seed coat [4]
0.53 g of vanillin per100g fresh green bean was measured in the six-month old vanilla beans, indicating that the beans used in this study maintain the biosynthetic capability of naturally-grown beans as regards glucovanillin accumulation
Summary
Pods of the vanilla orchid (Vanilla planifolia) accumulate large amounts of the flavor compound vanillin (3-methoxy, 4-hydroxy-benzaldehyde) as a glucoside during the later stages of their development. Genomic resources for determining the biosynthetic routes to these compounds and other flavor components in V. planifolia are currently limited. The fully-grown mature fruits of vanilla, called beans or pods, develop. A better understanding of the genetic complement of V. planifolia could provide information on the still-disputed biosynthetic route to vanillin [4], support mechanistic studies on other areas of the novel biochemistry of this species, such as the biosynthesis of novel seed coat lignins [5], and provide molecular markers to advance non-transgenic breeding programs targeting flavor quality, yield or disease resistance
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