Abstract
The anthocyanin biosynthesis attracts strong interest due to the potential antioxidant value and as an important morphological marker. However, the underlying mechanism of anthocyanin accumulation in plant tissues is not clearly understood. Here, a rice mutant with a purple color in the leaf blade, named pl6, was developed from wild type (WT), Zhenong 41, with gamma ray treatment. By map-based cloning, the OsPL6 gene was located on the short arm of chromosome 6. The multiple mutations, such as single nucleotide polymorphism (SNP) at −702, −598, −450, an insertion at −119 in the promoter, three SNPs and one 6-bp deletion in the 5′-UTR region, were identified, which could upregulate the expression of OsPL6 to accumulate anthocyanin. Subsequently, the transcript level of structural genes in the anthocyanin biosynthesis pathway, including OsCHS, OsPAL, OsF3H and OsF3′H, was elevated significantly. Histological analysis revealed that the light attenuation feature of anthocyanin has degraded the grana and stroma thylakoids, which resulted in poor photosynthetic efficiency of purple leaves. Despite this, the photoabatement and antioxidative activity of anthocyanin have better equipped the pl6 mutant to minimize the oxidative damage. Moreover, the contents of abscisic acid (ABA) and cytokanin (CK) were elevated along with anthocyanin accumulation in the pl6 mutant. In conclusion, our results demonstrate that activation of OsPL6 could be responsible for the purple coloration in leaves by accumulating excessive anthocyanin and further reveal that anthocyanin acts as a strong antioxidant to scavenge reactive oxygen species (ROS) and thus play an important role in tissue maintenance.
Highlights
Plants are decorated with a vast range of color through the accumulation of two major classes of pigments including flavonoids and carotenoids across the flowers, fruit, foliage, seeds and roots, etc.Flavonoids are divided into six major subgroups due to their structural complexity, including flavones, flavandiols, flavonols, chalcones, anthocyanins and pro-anthocyanidins [1]
The segregation in the F2 population showed a good fit to the 3:1 ratio (χ2 = 2.52 < χ2 0.05 = 3.84), suggesting that the purple leaf trait in pl6 was controlled by a single recessive nuclear gene
Anthocyanin biosynthesis is regulated by structural genes, yet their expression intensity is controlled by interaction of regulatory genes, which were encoded by transcription factors (TFs) known as MBW complex [9]
Summary
Plants are decorated with a vast range of color through the accumulation of two major classes of pigments including flavonoids and carotenoids across the flowers, fruit, foliage, seeds and roots, etc. Flavonoids are divided into six major subgroups due to their structural complexity, including flavones, flavandiols, flavonols, chalcones, anthocyanins and pro-anthocyanidins [1]. Anthocyanin in particular accumulated in vegetative and reproductive organs, and was responsible for the orange to blue range of colors [2]. The purple coloration to the non-edible part was used in breeding programs as a morphological marker to identify the varieties and to study the linkage analysis [6]. The purple apiculus color is widely used in the breeding program [7]
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