Cell-specific expression of homospermidine synthase, the entry enzyme of the pyrrolizidine alkaloid pathway in Senecio vernalis, in comparison with its ancestor, deoxyhypusine synthase.
Pyrrolizidine alkaloids (PAs) are constitutive plant defense compounds with a sporadic taxonomic occurrence. The first committed step in PA biosynthesis is catalyzed by homospermidine synthase (HSS). Recent evidence confirmed that HSS evolved by gene duplication from deoxyhypusine synthase (DHS), an enzyme involved in the posttranslational activation of the eukaryotic translation initiation factor 5A. To better understand the evolutionary relationship between these two enzymes, which are involved in completely different biological processes, we studied their tissue-specific expression. RNA-blot analysis, reverse transcriptase-PCR, and immunolocalization techniques demonstrated that DHS is constitutively expressed in shoots and roots of Senecio vernalis (Asteraceae), whereas HSS expression is root specific and restricted to distinct groups of endodermis and neighboring cortex cells located opposite to the phloem. All efforts to detect DHS by immunolocalization failed, but studies with promoter-beta-glucuronidase fusions confirmed a general expression pattern, at least in young seedlings of tobacco (Nicotiana tabacum). The expression pattern for HSS differs completely from its ancestor DHS due to the adaptation of HSS to the specific requirements of PA biosynthesis.
Moll
Stefanie
S
Institut für Pharmazeutische Biologie der Technischen Universität, Mendelssohnstrasse 1, D-38106 Braunschweig, Germany.
Anke
Sven
S
Kahmann
Uwe
U
Hänsch
Robert
R
Hartmann
Thomas
T
Ober
Dietrich
D
D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005966:Glucuronidase / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D016253:Microscopy, Immunoelectron; D008860:Microscopy, Ultraviolet; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000201:enzymology / Q000648:ultrastructure; D030821:Plants, Genetically Modified; D011763:Pyrrolizidine Alkaloids / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012674:Senecio / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D013379:Substrate Specificity; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics
D011763:Pyrrolizidine Alkaloids; D011993:Recombinant Fusion Proteins; D000587:Oxidoreductases Acting on CH-NH Group Donors; C063507:deoxyhypusine synthase; D019883:Alkyl and Aryl Transferases; C028376:homospermidine synthetase; D005966:Glucuronidase