Reference "A chalcone synthase with an unusual substrate preference is expressed in barley leaves in response to UV light and pathogen attack"

Reference ID

8613

Title

A chalcone synthase with an unusual substrate preference is expressed in barley leaves in response to UV light and pathogen attack

Source

Plant molecular biology, 1998, vol. 37, pp. 849-857

Authors (4)

Christensen-A-B	Gregersen-P-L
Schroder-J	Collinge-D-B

Abstract

A cDNA clone was isolated by differential hybridization from a library prepared
from barley leaves inoculated with the fungus Blumeria graminis f.sp. hordei
(Bgh). The open reading frame of the insert (designated HvCHS2) encoded a
polypeptide with 72-79% identity to chalcone synthases (CHS) and 65-68% identity
to stilbene synthases. Alignments of the amino acid sequence of HvCHS2 with the
consensus sequence of naringenin-CHS (EC 2.3.1.74) reveals significant
differences between HvCHS2 and naringenin-CHS. HvCHS2 transcripts accumulate
strongly in barley leaves in response to inoculation with Bgh, whereas only
insignificant accumulation of barley naringenin-CHS (CHS1) transcripts is seen
upon the inoculation. The accumulation of HvCHS2 transcripts is also elicited by
UV light. To compare the activity of HvCHS2 with the activity of CHS1, the two
enzymes were expressed in Escherichia coli. Both HvCHS2 and CHS1 catalyse the
formation of chalcones. However, HvCHS2 and CHS1 differ in their substrate
requirements. CHS1 uses cinnamoyl-CoA and 4-coumaroyl-CoA at comparable rates
whereas feruloyl-CoA is a poor substrate for this enzyme. In contrast, HvCHS2
converts feruloyl-CoA and caffeoyl-CoA at the highest rate whereas cinnamoyl-CoA
is a poor substrate. Thus, HvCHS2 is a novel pathogen and UV light induces
homoeriodictyol/eriodictyol CHS involved in the direct production of flavonoids
possessing multi-substituted B-rings.