title: Localization of strawberry (Fragaria x ananassa) and Methylobacterium extorquens genes of strawberry flavor biosynthesis in strawberry tissue by in situ hybridization.
abstract: Strawberry flavor is one of the most popular fruit flavors worldwide, with numerous applications in the food industry. In addition, the biosynthetic origin of the most important strawberry flavor components, such as 2,5-dimethyl-4-hydroxy-2H-furan-3-one (DMHF), is a challenging research area. DMHF's precursor, 2-hydroxy-propanal (or lactaldehyde), is biosynthesized by the endophytic bacterium Methylobacterium extorquens (M. extorquens). In particular, the alcohol dehydrogenase (ADH) enzymes of M. extorquens are involved in the biogenesis of DMHF precursors since they have the capacity to oxidize the strawberry-derived 1,2-propanediol to lactaldehyde. In this study, the expression of the endophytic ADH and the plant DMHF biosynthesis genes was examined in the tissues of raw and ripe strawberry receptacles by in situ hybridization. The presence of endophytic bacteria was studied in the same tissues by probes targeting bacterial 16S ribosomal ribonucleic acid. Hybridization signals of probes specific for endophytic ADH and plant DMHF biosynthesis genes, as well as bacteria-specific probes, were detected in the same locations. The probes were localized near the plasma membranes or intercellular spaces of cortical and vascular tissues of the receptacle, and intracellularly in the tissues of achenes. By localizing the expression of the endophytic methanol ADH and plant DMHF biosynthesis genes to the same tissues, we have reinforced our original hypothesis that an intimate symbiotic relationship between strawberry and endophytic cells exists and leads to the biosynthesis of DMHF.
authors: Department of Biology, University of Oulu, PO Box 3000, 90014, Oulu, Finland; Department of Chemistry, National and Kapodistrian University of Athens, Panepistimioupoli Zografou, 157 84, Athens, Greece. Electronic address: cnasopoulou@chem.uoa.gr.
authors: Constantina
authors: C
authors: Nasopoulou
authors: Department of Biology, University of Oulu, PO Box 3000, 90014, Oulu, Finland.
authors: Johanna
authors: J
authors: Pohjanen
authors: Department of Biology, University of Oulu, PO Box 3000, 90014, Oulu, Finland.
authors: Janne J
authors: JJ
authors: Koskimäki
authors: Department of Chemistry, National and Kapodistrian University of Athens, Panepistimioupoli Zografou, 157 84, Athens, Greece.
authors: Ioannis
authors: I
authors: Zabetakis
authors: Department of Biology, University of Oulu, PO Box 3000, 90014, Oulu, Finland.
authors: Anna Maria
authors: AM
authors: Pirttilä
mesh_terms: D000426:Alcohol Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D000447:Aldehydes / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D060026:Endophytes; D031985:Fragaria / Q000166:cytology / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology; D005638:Fruit / Q000235:genetics / Q000378:metabolism; D005663:Furans / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017403:In Situ Hybridization / Q000379:methods*; D000432:Methanol / Q000378:metabolism; D020601:Methylobacterium extorquens / Q000166:cytology / Q000235:genetics* / Q000502:physiology; D013559:Symbiosis
chemical_list: D000447:Aldehydes; D001426:Bacterial Proteins; D005663:Furans; C014634:lactaldehyde; D000426:Alcohol Dehydrogenase; C039281:furan; D000432:Methanol
keywords: Alcohol dehydrogenase enzymes; Endophyte; In situ hybridization; Methylobacterium extorquens; Strawberry flavor