Chalcone synthase and its functions in plant resistance

Abstract

Chalcone synthase (CHS, EC 2.3.1.74) is a key enzyme of the flavonoid/isoflavonoid biosynthesis pathway. Besides being part of the plant developmental program the CHS gene expression is induced in plants under stress conditions such as UV light, bacterial or fungal infection. CHS expression causes accumulation of flavonoid and isoflavonoid phytoalexins and is involved in the salicylic acid defense pathway. This review will discuss CHS and its function in plant resistance.

Fig. 1

Flavonoid biosynthetic pathway. ANS anthocyanidin synthase; AS aureusidin synthase; C4H cinnamate-4-hydroxylase; CHR chalcone reductase; DFR dihydroflavonol 4-reductase; DMID 7,2′-dihydroxy, 4′-methoxyisoflavanol dehydratase; F3H flavanone 3-hydroxylase; F3′H flavonoid 3′ hydroxylase; F3′5′H flavonoid 3′5′ hydroxylase; FS1/FS2 flavone synthase; I2′H isoflavone 2′-hydroxylase; IFR isoflavone reductase; IFS isoflavone synthase; IOMT isoflavone O-methyltransferase; LCR leucoanthocyanidin reductase; LDOX leucoanthocyanidin dioxygenase; OMT O-methyltransferase; PAL phenylalanine ammonia-lyase; RT rhamnosyl transferase; UFGT UDP flavonoid glucosyl transferase; VR vestitone reductase; STS stilbene synthase; FLS flavanol synthase. (Winkel ; Yamaguchi et al. ; KEGG pathways)

Fig. 2

Reaction catalyzed by chalcone synthase (CHS). In CHS, three amino acids play key roles in the catalytic functions of type III PKS: Cys164: active site, covalent binding site of starter residues and intermediates, His303 and Asn336: stabilization/activation of both starter (e.g. 4-coumarate) and extender units (malonyl-/acetyl-residues) (Ferrer et al. ; Bomati et al. ; modified by Schröder 2008)

Fig. 3

Alternate starter molecules and their in vitro reaction products catalyzed by CHS

Fig. 4

Bean CHS15 promoter and regulators. SBF silencer binding factor, H H-Box (CCTACC), G G-Box (CACGTG), a/a2 regulation loci