Abstract
BackgroundGinger (Zingiber officinale) and turmeric (Curcuma longa) accumulate important pharmacologically active metabolites at high levels in their rhizomes. Despite their importance, relatively little is known regarding gene expression in the rhizomes of ginger and turmeric.ResultsIn order to identify rhizome-enriched genes and genes encoding specialized metabolism enzymes and pathway regulators, we evaluated an assembled collection of expressed sequence tags (ESTs) from eight different ginger and turmeric tissues. Comparisons to publicly available sorghum rhizome ESTs revealed a total of 777 gene transcripts expressed in ginger/turmeric and sorghum rhizomes but apparently absent from other tissues. The list of rhizome-specific transcripts was enriched for genes associated with regulation of tissue growth, development, and transcription. In particular, transcripts for ethylene response factors and AUX/IAA proteins appeared to accumulate in patterns mirroring results from previous studies regarding rhizome growth responses to exogenous applications of auxin and ethylene. Thus, these genes may play important roles in defining rhizome growth and development. Additional associations were made for ginger and turmeric rhizome-enriched MADS box transcription factors, their putative rhizome-enriched homologs in sorghum, and rhizomatous QTLs in rice. Additionally, analysis of both primary and specialized metabolism genes indicates that ginger and turmeric rhizomes are primarily devoted to the utilization of leaf supplied sucrose for the production and/or storage of specialized metabolites associated with the phenylpropanoid pathway and putative type III polyketide synthase gene products. This finding reinforces earlier hypotheses predicting roles of this enzyme class in the production of curcuminoids and gingerols.ConclusionA significant set of genes were found to be exclusively or preferentially expressed in the rhizome of ginger and turmeric. Specific transcription factors and other regulatory genes were found that were common to the two species and that are excellent candidates for involvement in rhizome growth, differentiation and development. Large classes of enzymes involved in specialized metabolism were also found to have apparent tissue-specific expression, suggesting that gene expression itself may play an important role in regulating metabolite production in these plants.
Highlights
Ginger (Zingiber officinale) and turmeric (Curcuma longa) accumulate important pharmacologically active metabolites at high levels in their rhizomes
The resulting ArREST (Aromatic Rhizome expressed sequence tags (ESTs)) database contains a total of 50,139 ESTs (37,717 from ginger and 12,422 from turmeric) that assembled into 21,215 unigenes
Of the 21,215 unitrans identified in the ArREST database, 87.6% could be annotated with Gene Ontologies (GOs)
Summary
Ginger (Zingiber officinale) and turmeric (Curcuma longa) accumulate important pharmacologically active metabolites at high levels in their rhizomes. [6]-Gingerol has potential in treating chronic inflammation, such as in asthma and rheumatoid arthritis [4] This interest in the ginger and turmeric rhizome-associated diarylheptanoids and gingerols has prompted both enzyme assay and metabolic profiling-based inquiries into the biosynthesis of these compounds [2,5,6,7]. We do not understand why and how many advanced plants have “reverted” back to rhizomatous growth Such reversions have huge economic implications, being responsible for the invasiveness and hardiness of many of the world’s most significant weeds, such as purple nutsedge (Cyperus rotundus L.), Johnson grass (Sorghum halepense (L.) Pers.), and cogon grass (Imperata cylindrica (L.) Beauv.). Increasing our understanding of rhizome biology may have significant impacts on our understanding of how important medicinal compounds are produced, and on our ability to control important weedy species
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