title: Cassava plants with a depleted cyanogenic glucoside content in leaves and tubers. Distribution of cyanogenic glucosides, their site of synthesis and transport, and blockage of the biosynthesis by RNA interference technology.
abstract: Transgenic cassava (Manihot esculenta Crantz, cv MCol22) plants with a 92% reduction in cyanogenic glucoside content in tubers and acyanogenic (<1% of wild type) leaves were obtained by RNA interference to block expression of CYP79D1 and CYP79D2, the two paralogous genes encoding the first committed enzymes in linamarin and lotaustralin synthesis. About 180 independent lines with acyanogenic (<1% of wild type) leaves were obtained. Only a few of these were depleted with respect to cyanogenic glucoside content in tubers. In agreement with this observation, girdling experiments demonstrated that cyanogenic glucosides are synthesized in the shoot apex and transported to the root, resulting in a negative concentration gradient basipetal in the plant with the concentration of cyanogenic glucosides being highest in the shoot apex and the petiole of the first unfolded leaf. Supply of nitrogen increased the cyanogenic glucoside concentration in the shoot apex. In situ polymerase chain reaction studies demonstrated that CYP79D1 and CYP79D2 were preferentially expressed in leaf mesophyll cells positioned adjacent to the epidermis. In young petioles, preferential expression was observed in the epidermis, in the two first cortex cell layers, and in the endodermis together with pericycle cells and specific parenchymatic cells around the laticifers. These data demonstrate that it is possible to drastically reduce the linamarin and lotaustralin content in cassava tubers by blockage of cyanogenic glucoside synthesis in leaves and petioles. The reduced flux to the roots of reduced nitrogen in the form of cyanogenic glucosides did not prevent tuber formation.
authors.affiliation: Plant Biochemistry Laboratory, Department of Plant Biology, Center for Molecular Plant Physiology, Royal Veterinary and Agricultural University, Frederiksberg, Copenhagen, Denmark.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Jørgensen
authors.forename: Søren
authors.initials: S
authors.lastname: Bak
authors.forename: Peter Kamp
authors.initials: PK
authors.lastname: Busk
authors.forename: Charlotte
authors.initials: C
authors.lastname: Sørensen
authors.forename: Carl Erik
authors.initials: CE
authors.lastname: Olsen
authors.forename: Johanna
authors.initials: J
authors.lastname: Puonti-Kaerlas
authors.forename: Birger Lindberg
authors.initials: BL
authors.lastname: Møller
mesh_terms: D001693:Biological Transport, Active; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D018506:Gene Expression Regulation, Plant; D006027:Glycosides / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002365:Manihot / Q000378:metabolism*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009584:Nitrogen / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism*; D018547:Plant Stems / Q000378:metabolism; D035281:Plant Tubers / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D006027:Glycosides; D012333:RNA, Messenger; C007173:cyanogenic glycosides; D003577:Cytochrome P-450 Enzyme System; D009584:Nitrogen; D011188:Potassium