This presumably diverts metabolic flux away from anthocyanin synthesis towards naringenin and 3-deoxyanthocyanidin synthesis to meet immediate biochemical needs for plant defense (Lo and Nicholson, 1998).
Alfenito MR, Souer E, Goodman CD, Buell R, Mol J, Koes R, Walbot V 1998 Functional complementation of anthocyanin sequestration in the vacuole by widely divergent glutathione -transferases.
Anthocyanin synthesis in maize has been the subject of intense genetic, biochemical, and molecular experimentation. These studies have identified the structural genes encoding enzymes and transporters of the biosynthetic pathway, as well as the key regulatory genes. The picture that emerges from these analyses is that pigmentation in the maize aleurone is orchestrated by a complex regulatory network involving interaction among tissue-specific, developmental and environmental factors.
Tyr is the precursor of melanin that exits in both animals and plants [16-18]. However, until now it has been unclear whether Tyr induces anthocyanin biosynthesis. In this study the seedlings of Arabidopsis thaliana were treated with exogenous Tyr for analysis of anthocyanin accumulation and the expression of the anthocyanin biosynthesis genes and the WD-repeat/Myb/bHLH transcription factor genes to determine whether Tyr induces anthocyanin biosynthesis.
The measurement of anthocyanin was performed as described by Deikman and Hammer . The preweighed seedlings were placed into 1 mL extraction buffer (18% 1-propanol, 1% HCl, and 81% water), boiled for 3 min and then incubated in darkness overnight at room temperature. The absorbance of the supernatant was measured at 535 nm and 650 nm. The anthocyanin content was determined by the formula (A535-A650) g−1 fresh weight (FW). There were six samples per each treatment.
Accumulation of anthocyanins in plants is stimulated by diverse developmental signals, sugar, plant hormone, and environmental stresses [6-11]. Jasmonate (JA), a kind of plant hormones, induces anthocyanin accumula-
In order to investigate whether Tyr induces anthocyanin biosynthesis in plants, the Arabidopsis thaliana seedlings were treated with exogenous Tyr. Upon Tyr treatment, pigmentation appeared in back of leaves and it was more obvious when treated with high concentrations of Tyr (). The content of anthocyanin was increased in a dose-dependent manner of Tyr (). These results indicated that Tyr is able to induce anthocyanin accumulation.
Anthocyanins are widely found in plants and are responsible for the purple coloration of plants. Anthocyanin biosynthesis is induced by environmental stresses, plant hormones, sugar, and so on. Tyrosine (Tyr) is the precursor of melanin that exits in both animals and plants. However, until now it has been unknown whether Tyr induces anthocyanin biosynthesis. In this study, the seedlings of Arabidopsis thaliana were treated with exogenous Tyr and then the anthocyanin accumulation was determined. The results showed that Tyr induced anthocyanin accumulation in Arabidopsis thaliana in a dose-dependent manner. Furthermore, the expression of the late anthocyanin biosynthetic genes including DFR, LDOX, and UF3GT, and the transcription factor genes PAP1, PAP2, and EGL3 was induced by Tyr. Taken together, these results demonstrated that Tyr is able to induce anthocyanin accumulation and suggested that Tyr up-regulates transcription factors PAP1, PAP2, and EGL3, which mediates the expression of the late anthocyanin biosynthetic genes and then induces anthocyanin biosynthesis.
late anthocyanin biosynthetic genes DFR, LDOX, and UF3GT, and transcription factors PAP1 and PAP2 (). However, the expression of transcription factor GL3 was not induced by Tyr (). Instead, Tyr induces the expression of transcription factor EGL3 (). Therefore, Tyr and JA modulate the expression of late anthocyanin biosynthetic genes by mediating the same Myb transcription factors PAP1 and PAP2, but the different bHLH transcription factors EGL3 and GL3.
The () gene in maize encodes a [EC 188.8.131.52] that performs the last genetically defined step in anthocyanin biosynthesis -- tagging cyanidin-3-glucoside with glutathione, allowing for transport to the vacuole via a tonoplast Mg-ATP-requiring GS-X pump (Marrs and Walbot, 1997; Lu et al, 1998; Alfenito et al, 1998).
Understanding which genes contribute to evolutionary change and the nature of the alterations in them are fundamental challenges in evolution. We analyzed regulatory and enzymatic genes in the maize anthocyanin pathway as related to the evolution of anthocyanin-pigmented kernels in maize from colorless kernels of its progenitor, teosinte. Genetic tests indicate that teosinte possesses functional alleles at all enzymatic loci. At two regulatory loci, most teosintes possess alleles that encode functional proteins, but ones that are not expressed during kernel development and not capable of activating anthocyanin biosynthesis there. We investigated nucleotide polymorphism at one of the regulatory loci, c1. Several observations suggest that c1 has not evolved in a strictly neutral manner, including an exceptionally low level of polymorphism and a biased representation of haplotypes in maize. Curiously, sequence data show that most of our teosinte samples possess a promoter element necessary for the activation of the anthocyanin pathway during kernel development, although genetic tests indicate that teosinte c1 alleles are not active during kernel development. Our analyses suggest that the evolution of the purple kernels resulted from changes in cis regulatory elements at regulatory loci and not changes in either regulatory protein function nor the enzymatic loci.