Uncovering the evolutionary origin of blue anthocyanins in cereal grains

Abstract

Summary Functional divergence after gene duplication plays a central role in plant evolution. Among cereals, only Hordeum vulgare (barley), Triticum aestivum (wheat) and Secale cereale (rye) accumulate delphinidin‐derived (blue) anthocyanins in the aleurone layer of grains, whereas Oryza sativa (rice), Zea mays (maize) and Sorghum bicolor (sorghum) do not. The underlying genetic basis for this natural occurrence remains elusive. Here, we mapped the barley Blx1 locus involved in blue aleurone to an approximately 1.13 Mb genetic interval on chromosome 4HL, thus identifying a trigenic cluster named MbHF35 (containing HvMYB4H, HvMYC4H and HvF35H). Sequence and expression data supported the role of these genes in conferring blue‐coloured (blue aleurone) grains. Synteny analyses across monocot species showed that MbHF35 has only evolved within distinct Triticeae lineages, as a result of dispersed gene duplication. Phylogeny analyses revealed a shared evolution pattern for MbHF35 in Triticeae, suggesting that these genes have co‐evolved together. We also identified a Pooideae‐specific flavonoid 3′,5′‐hydroxylase (F3′5′H) lineage, termed here Mo_F35H2, which has a higher amino acid similarity with eudicot F3′5′Hs, demonstrating a scenario of convergent evolution. Indeed, selection tests identified 13 amino acid residues in Mo_F35H2 that underwent positive selection, possibly driven by protein thermostablility selection. Furthermore, through the interrogation of barley germplasm there is evidence that HvMYB4H and HvMYC4H have undergone human selection. Collectively, our study favours blue aleurone as a recently evolved trait resulting from environmental adaptation. Our findings provide an evolutionary explanation for the absence of blue anthocyanins in other cereals and highlight the importance of gene functional divergence for plant diversity and environmental adaptation.

Evolutionary dynamic analyses on monocot flavonoid 3′-hydroxylase gene family reveal evidence of plant-environment interaction

“…F3'H and F3'5'H are close homologs in the cytochrome P450 superfamily, responsible for the production of red and blue anthocyanins, respectively. A similar observation has been made on monocot F3'5'H gene subfamily [48], in which positive selection has been shown to drive the emergence of a separate F3'5'H lineage responsible for the accumulation of blue anthocyanins in Triticeae grains. The selection on monocot F3'5'H was suggested to have resulted from plants' adaptation to strong light or heat stresses.…”

“…5 Transcriptional profiles of monocot F3'Hs. a LOC_Os10g16974 (Class II) and LOC_Os10g17260 (Class I) in rice; b HORVU6Hr1G002400 (Class II) and HORVU1Hr1G094880 (Class I) in barley; c Sobic.004G200800, Sobic.004G200833, Sobic.004G200900, Sobic.004G201100 (Class I) and Sobic.009G162500 (Class II) in Sorghum; d Zm00008a016611, Zm00008a022212 (Class I) and Zm00008a031477 (Class II) in maize gene families (MYB, MYC and F3'5'H) from the anthocyanin biosynthetic pathway in monocot plants [48]. Noteworthy, we found that tandem duplication and proximal duplication have contributed to the expansion of F3'Hs specifically in S. bicolor and O. sativa.…”

“…Due to the close homology between F3'5'H and F3'H, genuine F3'H homologs were identified by a method as described in a previous study [48]. Twelve monocot crops and twelve eudicot species were included.…”

Overexpression of ThMYC4E Enhances Anthocyanin Biosynthesis in Common Wheat

“…The blue grain trait was speculated to be controlled by one major gene locus and ThMYC4E resides in this region. Recently, a trigenic cluster (bHLH-MYB-F3 5 H) was reported to exist in the homologous region to Ba1 in barley [33]. The trigenic cluster was thought to play an important role in conferring the blue aleurone trait in cereal [33].…”

“…Recently, a trigenic cluster (bHLH-MYB-F3 5 H) was reported to exist in the homologous region to Ba1 in barley [33]. The trigenic cluster was thought to play an important role in conferring the blue aleurone trait in cereal [33]. This could explain the reason ThMYC4E overexpression did not induce the blue grain trait.…”