Functional characterization of key structural genes in rice flavonoid biosynthesis.
Rice is a model system for monocot but the molecular features of rice flavonoid biosynthesis have not been extensively characterized. Rice structural gene homologs encoding chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3'-hydroxylase (F3'H), dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase (ANS) were identified by homology searches. Unique differential expression of OsF3H, OsDFR, and OsANS1 controlled by the Pl(w) locus, which contains the R/B-type regulatory genes OSB1 and OSB2, was demonstrated during light-induced anthocyanin accumulation in T65-Plw seedlings. Previously, F3H genes were often considered as early genes co-regulated with CHS and CHI genes in other plants. In selected non-pigmented rice lines, OSB2 is not expressed following illumination while their expressed OSB1sequences all contain the same nucleotide change leading to the T(64) M substitution within the conserved N-terminal interacting domain. Furthermore, the biochemical roles of the expressed rice structural genes (OsCHS1, OsCHI, OsF3H, and OsF3'H) were established in planta for the first time by complementation in the appropriate Arabidopsis transparent testa mutants. Using yeast two-hybrid analysis, OsCHS1 was demonstrated to interact physically with OsF3H, OsF3'H, OsDFR, and OsANS1, suggesting the existence of a macromolecular complex for anthocyanin biosynthesis in rice. Finally, flavones were identified as the major flavonoid class in the non-pigmented T65 seedlings in which the single-copy OsF3H gene was not expressed. Competition between flavone and anthocyanin pathways was evidenced by the significant reduction of tricin accumulation in the T65-Plw seedlings.
Shih
Chun Hat
CH
School of Biological Sciences, The University of Hong Kong, Hong Kong, China.
Chu
Hung
H
Tang
Lee Kwan
LK
Sakamoto
Wataru
W
Maekawa
Masahiko
M
Chu
Ivan K
IK
Wang
Mingfu
M
Lo
Clive
C
D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D005419:Flavonoids / Q000096:biosynthesis* / Q000737:chemistry; D017343:Genes, Plant; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D012275:Oryza / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D036226:Seedlings / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D020798:Two-Hybrid System Techniques
D005419:Flavonoids; D010940:Plant Proteins; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D000429:Alcohol Oxidoreductases; C056570:dihydroflavanol 4-reductase; D010105:Oxygenases; C048797:flavanone 3-dioxygenase; C038888:flavonoid 3'-hydroxylase; C118159:anthocyanidin synthase; D000217:Acyltransferases; C020141:flavanone synthetase