Duplicated flavonoid 3'-hydroxylase and flavonoid 3', 5'-hydroxylase genes in barley genome

Alexander V Vikhorev, Ksenia V Strygina, Elena K Khlestkina
PeerJ 2019, 7: e6266

Background: Anthocyanin compounds playing multiple biological functions can be synthesized in different parts of barley ( Hordeum vulgare L.) plant. The diversity of anthocyanin molecules is related with branching the pathway to alternative ways in which dihydroflavonols may be modified either with the help of flavonoid 3'-hydroxylase ( F 3' H ) or flavonoid 3',5'-hydroxylase ( F 3'5' H )-the cytochrome P450-dependent monooxygenases. The F3 ' H and F3 '5' H gene families are among the least studied anthocyanin biosynthesis structural genes in barley. The aim of this study was to identify and characterise duplicated copies of the F3 ' H and F 3'5' H genes in the barley genome.

Results: Four copies of the F3 '5' H gene (on chromosomes 4HL, 6HL, 6HS and 7HS) and two copies of the F3 ' H gene (on chromosomes 1HL and 6HS) were identified in barley genome. These copies have either one or two introns. Amino acid sequences analysis demonstrated the presence of the flavonoid hydroxylase-featured conserved motifs in all copies of the F 3' H and F 3'5' H genes with the exception of F 3'5' H -3 carrying a loss-of-function mutation in a conservative cytochrome P450 domain. It was shown that the divergence between F3 ' H and F3 '5' H genes occurred 129 million years ago (MYA) before the emergence of monocot and dicot plant species. The F3 ' H copy approximately occurred 80 MYA; the appearance of F3 '5' H copies occurred 8, 36 and 91 MYA. qRT-PCR analysis revealed the tissue-specific activity for some copies of the studied genes. The F3 ' H -1 gene was transcribed in aleurone layer, lemma and pericarp (with an increased level in the coloured pericarp), whereas the F3 ' H-2 gene was expressed in stems only. The F3 '5' H-1 gene was expressed only in the aleurone layer, and in a coloured aleurone its expression was 30-fold higher. The transcriptional activity of F3 '5' H-2 was detected in different tissues with significantly higher level in uncoloured genotype in contrast to coloured ones. The F3 '5' H-3 gene expressed neither in stems nor in aleurone layer, lemma and pericarp. The F3 '5' H-4 gene copy was weakly expressed in all tissues analysed.

Conclusion: F3 ' H and F3 '5' H -coding genes involved in anthocyanin synthesis in H. vulgare were identified and characterised, from which the copies designated F3 ' H-1 , F3 ' H-2 , F3 '5' H-1 and F3 '5' H-2 demonstrated tissue-specific expression patterns. Information on these modulators of the anthocyanin biosynthesis pathway can be used in future for manipulation with synthesis of diverse anthocyanin compounds in different parts of barley plant. Finding both the copies with tissue-specific expression and a copy undergoing pseudogenization demonstrated rapid evolutionary events tightly related with functional specialization of the duplicated members of the cytochrome P450-dependent monooxygenases gene families.

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