K. Haralampidis et al., A new class of oxidosqualene cyclases directs synthesis of antimicrobial phytoprotectants in monocots, P NAS US, 98(23), 2001, pp. 13431-13436
Citations number
43
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Many plants synthesize antimicrobial secondary metabolites as part of their
normal program of growth and development, often sequestering them in tissu
es where they may protect against microbial attack. These include glycosyla
ted triterpenoids (saponins), natural products that are exploited by man fo
r a variety of purposes including use as drugs [Hostettmann, K. & Marston,
A. (1995) Saponins (Cambridge Univ. Press, Cambridge, U.K.)]. Very little i
s known about the genes required for the synthesis of this important family
of secondary metabolites in plants. Here we show the novel oxidosqualene c
yclase AsbAS1 catalyzes the first committed step in the synthesis of antifu
ngal triterpenoid saponins that accumulate in oat roots. We also demonstrat
e that two sodium azide-generated saponin-deficient mutants of oat, which d
efine the Sad1 genetic complementation group, are defective in the gene enc
oding this enzyme and provide molecular genetic evidence indicating a direc
t link between AsbAS1, triterpenoid saponin biosynthesis, and disease resis
tance. Orthologs of AsbAS1 are absent from modern cereals and may have been
lost during selection, raising the possibility that this gene could be exp
loited to enhance disease resistance in crop plants.