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.

中文翻译：

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发现谷物中蓝色花色苷的进化起源。

基因复制后的功能差异在植物进化中起着核心作用。在谷物中，只有大麦（Hordeum vulgare）（大麦），小麦（Erictic aestivum）（小麦）和黑麦（Secale）谷物（黑麦）在谷物糊粉层中积累了由翠雀素衍生的（蓝色）花青素，而水稻（Oryza sativa）（大米），玉米（Zea mays）（玉米）和高粱（Sorghum）双色（高粱）不。这种自然发生的潜在遗传基础仍然难以捉摸。在这里，我们将涉及蓝色糊粉的大麦Blx1基因座定位到4HL染色体上大约1.13 Mb的遗传区间，从而鉴定了一个名为MbHF35的三基因簇（包含HvMYB4H，HvMYC4H和HvF35H）。序列和表达数据支持了这些基因在赋予蓝色（蓝色糊粉）谷物中的作用。对单子叶植物物种的同构分析显示，由于分散的基因重复，MbHF35仅在不同的小麦属中进化。系统发育分析揭示了小麦中MbHF35共有的进化模式，表明这些基因共同进化。我们还鉴定了一个Pooideae特异的类黄酮3'，5'-羟化酶（F3'5'H）谱系，在这里称为Mo_F35H2，它与真双子叶植物F3'5'Hs具有更高的氨基酸相似性，证明了融合进化的可能性。实际上，选择测试确定了Mo_F35H2中的13个氨基酸残基经历了正选择，这可能是由蛋白质热稳定性选择驱动的。此外，通过对大麦种质的询问，有证据表明HvMYB4H和HvMYC4H已经过人类选择。总的来说，我们的研究偏爱蓝色糊粉作为一种因环境适应而近来进化的性状。我们的发现为其他谷物中不存在蓝色花色苷提供了进化解释，并突出了基因功能差异对植物多样性和环境适应性的重要性。