Abstract
The biosynthesis of plant secondary metabolites is associated with morphological and metabolic differentiation. As a consequence, gene expression profiles can change drastically, and primary and secondary metabolites, including intermediate and end-products, move dynamically within and between cells. However, little is known about the molecular mechanisms underlying differentiation and transport mechanisms. In this study, we performed a transcriptome analysis of Petunia axillaris subsp. parodii, which produces various volatiles in its corolla limbs and emits metabolites to attract pollinators. RNA-sequencing from leaves, buds, and limbs identified 53,243 unigenes. Analysis of differentially expressed genes, combined with gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses, showed that many biological processes were highly enriched in limbs. These included catabolic processes and signaling pathways of hormones, such as gibberellins, and metabolic pathways, including phenylpropanoids and fatty acids. Moreover, we identified five transporter genes that showed high expression in limbs, and we performed spatiotemporal expression analyses and homology searches to infer their putative functions. Our systematic analysis provides comprehensive transcriptomic information regarding morphological differentiation and metabolite transport in the Petunia flower and lays the foundation for establishing the specific mechanisms that control secondary metabolite biosynthesis in plants.
Highlights
Plants produce various secondary metabolites to adapt to their environments
To identify differentially expressed genes (DEGs) in limbs, we compared RPKM values of unigenes among leaves, buds, and limbs, and found that 2,576 unigenes were expressed highly in limbs. These unigenes were analyzed further using gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) to investigate the processes and pathways enriched in limbs (Fig 2 and Table 1)
Transcriptome analysis from P. axillaris limbs, buds, and leaves identified 53,243 unigenes, with 2,576 unigenes highly expressed in limbs
Summary
Plants produce various secondary metabolites to adapt to their environments. Most of these metabolites are produced only in specific organs, tissues, and cells, where biosynthetic. Most family members have 12 TMDs and two nucleotide-binding domains and function as transporters to a diverse set of substrates, including plant hormones, secondary metabolites, and lipidic monomers. These proteins are implicated as playing an important role in plant development, defense mechanisms, and morphology, among others. Five transporters were identified with high expression in limbs, and their spatiotemporal expression patterns and physiological functions were analyzed and discussed These results aid in providing a comprehensive characterization of the genes associated with morphological and metabolic differentiations in flower cells, and they generate new insight into the molecular mechanisms of transporter-dependent metabolite movement that is essential for organ development and secondary metabolite production
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