Abstract
BackgroundThe maize (Zea mays) red aleurone1 (pr1) encodes a CYP450-dependent flavonoid 3’-hydroxylase (ZmF3’H1) required for the biosynthesis of purple and red anthocyanin pigments. We previously showed that Zmf3’h1 is regulated by C1 (Colorless1) and R1 (Red1) transcription factors. The current study demonstrates that, in addition to its role in anthocyanin biosynthesis, the Zmf3’h1 gene also participates in the biosynthesis of 3-deoxyflavonoids and phlobaphenes that accumulate in maize pericarps, cob glumes, and silks. Biosynthesis of 3-deoxyflavonoids is regulated by P1 (Pericarp color1) and is independent from the action of C1 and R1 transcription factors.ResultsIn maize, apiforol and luteoforol are the precursors of condensed phlobaphenes. Maize lines with functional alleles of pr1 and p1 (Pr1;P1) accumulate luteoforol, while null pr1 lines with a functional or non-functional p1 allele (pr1;P1 or pr1;p1) accumulate apiforol. Apiforol lacks a hydroxyl group at the 3’-position of the flavylium B-ring, while luteoforol has this hydroxyl group. Our biochemical analysis of accumulated compounds in different pr1 genotypes showed that the pr1 encoded ZmF3’H1 has a role in the conversion of mono-hydroxylated to bi-hydroxylated compounds in the B-ring. Steady state RNA analyses demonstrated that Zmf3’h1 mRNA accumulation requires a functional p1 allele. Using a combination of EMSA and ChIP experiments, we established that the Zmf3’h1 gene is a direct target of P1. Highlighting the significance of the Zmf3’h1 gene for resistance against biotic stress, we also show here that the p1 controlled 3-deoxyanthocyanidin and C-glycosyl flavone (maysin) defence compounds accumulate at significantly higher levels in Pr1 silks as compared to pr1 silks. By virtue of increased maysin synthesis in Pr1 plants, corn ear worm larvae fed on Pr1; P1 silks showed slower growth as compared to pr1; P1 silks.ConclusionsOur results show that the Zmf3’h1 gene participates in the biosynthesis of phlobaphenes and agronomically important 3-deoxyflavonoid compounds under the regulatory control of P1.
Highlights
The maize (Zea mays) red aleurone1 encodes a CYP450-dependent flavonoid 3’-hydroxylase (ZmF3’H1) required for the biosynthesis of purple and red anthocyanin pigments
The genetic and biochemical analysis of well-defined genetic stocks with combination of pr1 and p1 alleles we demonstrate that P1 regulated biosynthesis of 3deoxyflavonoids in pericarps, cob glumes, and silks requires a functional Zmf3’h1 gene
The Zmf3’h1 has been shown to be required for the formation of purple anthocyanins in kernel aleurones [24], changes in pigment intensity has been observed in phlobaphene accumulating tissues in the presence of a functional Zmf3’h1 gene [3]
Summary
The maize (Zea mays) red aleurone (pr1) encodes a CYP450-dependent flavonoid 3’-hydroxylase (ZmF3’H1) required for the biosynthesis of purple and red anthocyanin pigments. We previously showed that Zmf3’h1 is regulated by C1 (Colorless1) and R1 (Red1) transcription factors. The current study demonstrates that, in addition to its role in anthocyanin biosynthesis, the Zmf3’h1 gene participates in the biosynthesis of 3-deoxyflavonoids and phlobaphenes that accumulate in maize pericarps, cob glumes, and silks. Biosynthesis of 3-deoxyflavonoids is regulated by P1 (Pericarp color1) and is independent from the action of C1 and R1 transcription factors. The maize (Zea mays) flavonoid biosynthesis provides an excellent system to study gene interaction in plants because of its extensive characterization at genetic, biochemical, and molecular levels [1]. Different flavonoid compounds share the same basic skeleton of the flavannucleus consisting of two aromatic rings with six carbon atoms (ring A and B) which are interconnected by a PAL C4H Phenylalanine 4-Coumarate
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