Date Published: June 14, 2018
Publisher: Public Library of Science
Author(s): Ikuko Amano, Sakihito Kitajima, Hideyuki Suzuki, Takao Koeduka, Nobukazu Shitan, Serena Aceto.
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.
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 enzymes are expressed. Therefore, the proper timing and regulation of these enzymes is associated with morphological and metabolic differentiation of plant organs .
Transcriptome analysis from P. axillaris limbs, buds, and leaves identified 53,243 unigenes, with 2,576 unigenes highly expressed in limbs. GO and KEGG analyses of DEG clarified that genes involved in hormone response, drought tolerance, and phenylpropanoid biosynthesis were enriched and implicated in morphological and metabolic differentiation in the flower. Several candidate genes for VBP transcription factors and biosynthetic enzymes were identified, which would be useful for characterization of VBP biosynthesis in P. axillaris. In addition, five transporter genes highly expressed in limbs were identified. Spatiotemporal expression analysis revealed their distinct expression profiles, with a possible involvement of these transporters in morphological differentiation and metabolite transport. PaNPF3.1 might be involved in flower opening and volatile production through its gibberellin transport. PaSWEET1 would supply sugars as energy for flowering and volatile biosynthesis. PaSWEET15 might play an important role in volatile production and seed production through its sucrose transport. PaABCG1 would function in the formation of apoplastic diffusion barrier like cutin and suberin by transport of lipidic compounds. PaURGT4 would transport galactose into Golgi lumen, which leads to cell wall biosynthesis. These findings provide a foundation to further the comprehensive identification of the genes involved in organ development and metabolite production, and they further elucidate the dynamics of metabolite transport in plant cells producing secondary metabolites.