Abstract
Several plant species can generate enough heat to increase their internal floral temperature above ambient temperature. Among thermogenic plants, Arum concinnatum shows the highest respiration activity during thermogenesis. However, an overall understanding of the genes related to plant thermogenesis has not yet been achieved. In this study, we performed de novo transcriptome analysis of flower organs in A. concinnatum. The de novo transcriptome assembly represented, in total, 158,490 non-redundant transcripts, and 53,315 of those showed significant homology with known genes. To explore genes associated with thermogenesis, we filtered 1266 transcripts that showed a significant correlation between expression pattern and the temperature trend of each sample. We confirmed five putative alternative oxidase transcripts were included in filtered transcripts as expected. An enrichment analysis of the Gene Ontology terms for the filtered transcripts suggested over-representation of genes involved in 1-deoxy-d-xylulose-5-phosphate synthase (DXS) activity. The expression profiles of DXS transcripts in the methyl-d-erythritol 4-phosphate (MEP) pathway were significantly correlated with thermogenic levels. Our results suggest that the MEP pathway is the main biosynthesis route for producing scent monoterpenes. To our knowledge, this is the first report describing the candidate pathway and the key enzyme for floral scent production in thermogenic plants.
Highlights
Several plant species can generate enough heat to increase their internal floral temperature above ambient temperature
The expression profiles of D-xylulose-5-phosphate synthase (DXS) transcripts in the methyl-D-erythritol 4-phosphate (MEP) pathway were significantly correlated with thermogenic levels
Only alternative oxidase (AOX) showed significantly higher correlation; other genes for mitochondrial energy-dissipating enzymes were not significantly correlated with the thermogenic levels of each organ (Table 1). These results suggest that gene expression for AOX plays a critical role in thermogenesis of A. concinnatum, and uncoupling protein (UCP), NDA and NDB may act in a rather ubiquitous fashion in this nonthermoregulatory plant
Summary
Several plant species can generate enough heat to increase their internal floral temperature above ambient temperature. There are three major benefits of heat production in thermogenic plants: (1) to protect the reproductive process from low temperatures[4,17], (2) to reward insect pollinators in the flower by providing a warm environment[18], and (3) to attract insect pollinators by volatilizing floral scent compounds[19] All these roles are important for underwww.nature.com/scientificreports standing the biological significance of thermogenesis in plants, which involves a substantial energy cost. Detailed molecular mechanisms (e.g., expression of protein and regulation of activity) of AOX and UCP have been reported[28,33,36,37,38,39,40]; an overall understanding of the genes related to plant thermogenesis has not yet been achieved. These differences in heat production levels among the floral parts are convenient for comparing the molecules related to heat production in an individual
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