7 research outputs found
CYP72A67 catalyses a key oxidative step in Medicago truncatula hemolytic saponin biosynthesis
In the Medicago genus, triterpenic saponins are bioactive secondary metabolites constitutively synthesized
in the aerial and subterranean parts of plants via the isoprenoid pathway. Exploitation of saponins
as pharmaceutics, agrochemicals and in the food and cosmetic industries has raised interest in identifying
the enzymes involved in their synthesis. We have identified a cytochrome P450 (CYP72A67) involved in
hemolytic sapogenin biosynthesis by a reverse genetic TILLING approach in a Medicago truncatula ethylmethanesulfonate
(EMS) mutagenized collection. Genetic and biochemical analyses, mutant complementation,
and expression of the gene in a microsome yeast system showed that CYP72A67 is responsible for
hydroxylation at the C-2 position downstreamof oleanolic acid synthesis. The affinity of CYP72A67 for substrates
with different substitutions at multiple carbon positions was investigated in the same in vitro yeast
system, and in relation to two other CYP450s (CYP72A68) responsible for the production of medicagenic
acid, the main sapogenin in M. truncatula leaves and roots. Full sib mutant and wild-type plants were
compared for their sapogenin profile, expression patterns of the genes involved in sapogenin synthesis,
and response to inoculation with Sinorhizobium meliloti. The results obtained allowed us to revise the
hemolytic sapogenin pathway in M. truncatula and contribute to highlighting the tissue specificities
(leaves/roots) of sapogenin synthesis