1 research outputs found
Biosynthesis of abscisic acid in fungi: identification of a sesquiterpene cyclase as the key enzyme in Botrytis cinerea
While abscisic acid (ABA) is known as a hormone
produced by plants through the carotenoid pathway,
a small number of phytopathogenic fungi are also
able to produce this sesquiterpene but they use a dis-
tinct pathway that starts with the cyclization of
farnesyl diphosphate (FPP) into 2Z,4E-a-ionylidene-
ethane which is then subjected to several oxidation
steps. To identify the sesquiterpene cyclase (STC)
responsible for the biosynthesis of ABA in fungi, we
conducted a genomic approach in Botrytis cinerea.
The genome of the ABA-overproducing strain
ATCC58025 was fully sequenced and five STC-coding
genes were identified. Among them, Bcstc5 exhibits
an expression profile concomitant with ABA produc-
tion. Gene inactivation, complementation and
chemical analysis demonstrated that BcStc5/BcAba5
is the key enzyme responsible for the key step of
ABA biosynthesis in fungi. Unlike what is observed
for most of the fungal secondary metabolism genes
the key enzyme-coding gene Bcstc5/Bcaba5 is not
clustered with the other biosynthetic genes, i.e.
Bcaba1 to Bcaba4 that are responsible for the oxida-
tive transformation of 2Z,4E-a-ionylideneethane.
Finally, our study revealed that the presence of the
Bcaba genes among Botrytis species is rare and that
the majority of them do not possess the ability to pro-
duce ABA