Phenylpropanoid compounds encompass a wide range of structural classes and biological functions. Limiting discussion to stress-induced phenylpropanoids eliminates few of the structural classes, because many compounds thst are constitutive in one plant species or tissue can be induced by various stresses in another species or in another tissue of the same plant (Beggs et al., 1987; Christie et al., 1994).

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Stress-Induced Phenylpropanoid Metabolism.

The role of flavonoids as the major red, blue, and purple pigments in plants has gained these secondary products a great deal of attention over the years. From the first description of acid and base effects on plant pigments by Robert Boyle in 1664 to the characterization of structural and

Flavonoid Biosynthesis. A Colorful Model for Genetics, Biochemistry, Cell Biology, and Biotechnology

https://www.cell.com/cell/pdf/0092-8674(93)90330-S.pdf

Mutations of a mutS homolog in hereditary nonpolyposis colorectal cancer

Some cases of hereditary nonpolyposis colorectal cancer (HNPCC) are due to alterations in a mutS-related mismatch repair gene. A search of a large database of expressed sequence tags derived from random complementary DNA clones revealed three additional human mismatch repair genes, all related to the bacterial mutL gene. One of these genes (hMLH1) resides on chromosome 3p21, within 1 centimorgan of markers previously linked to cancer susceptibility in HNPCC kindreds. Mutations of hMLH1 that would disrupt the gene product were identified in such kindreds, demonstrating that this gene is responsible for the disease. These results suggest that defects in any of several mismatch repair genes can cause HNPCC.

https://science.sciencemag.org/content/sci/263/5153/1625.full.pdf

Mutation of a mutL homolog in hereditary colon cancer

Previous studies suggested that one or more genes on chromosome 5q21 are responsible for the inheritance of familial adenomatous polyposis (FAP) and Gardner's syndrome (GS), and contribute to tumor development in patients with noninherited forms of colorectal cancer. Two genes on 5q21 that are tightly linked to FAP (MCC and APC) were found to be somatically altered in tumors from sporadic colorectal cancer patients. One of the genes (APC) was also found to be altered by point mutation in the germ line of FAP and GS patients. These data suggest that more than one gene on chromosome 5q21 may contribute to colorectal neoplasia, and that mutations of the APC gene can cause both FAP and GS. The identification of these genes should aid in understanding the pathogenesis of colorectal neoplasia and in the diagnosis and counseling of patients with inherited predispositions to colorectal cancer.

https://science.sciencemag.org/content/sci/253/5020/665.full.pdf

Mutations of chromosome 5q21 genes in FAP and colorectal cancer patients

Flavonoids represent a large class of secondary plant metabolites, of which anthocyanins are the most conspicuous class, dueto the wide range of colors resulting from their synthesis. Anthocyanins are important to many diverse functions within plants. Synthesis of anthocyanins in petals is undoubtedly intended to attract pollinators, whereas anthocyanin synthesis in seeds and fruits may aid in seed dispersal. Anthocyanins and other flavonoids can also be important as feeding deterrents and as protection against damage from UV irradiation. The existence of such a diverse range of functions and types of anthocyanins raises questions about how these compounds are synthesized and how their synthesis is regulated. The study of the genetics of anthocyanin synthesis began last century with Mendel’s work on flower color in peas. Since that time, there have been periods of intensive study into the genetics and biochemistry of pigment production in a number of different species. In the early studies, genetic loci were correlated with easily observable color changes. After the structures of anthocyanins and other flavonoids were determined, it was possible to correlate single genes with particular structural alterations of anthocyanins or with the presence or absence of particular flavonoids. Mutations in anthocyanin genes have been studied for many years because they are easily identified and because they generally have no deleterious effect on plant growth and development. In most cases, mutations affecting different steps of the anthocyanin biosynthesis pathway were isolated and characterized well before their function was identified or the corresponding gene was isolated. More recently, many genes involved in the biosynthesis of anthocyanin pigments have been isolated and characterized using recombinant DNA technologies. Three species have been particularly important for elucidating the anthocyanin biosynthetic pathway and for isolating genes controlling the biosynthesis of flavonoids: maize (Zea mays), snapdragon (Anfirrhinum majus), and petunia (Wtunia hybrida). Petunia has more recently become the organism of choice for isolating flavonoid biosynthetic genes and studying their interactions and regulation. At least 35 genes are known to affect flower color in petuniawiering and de Vlaming, 1984). Because this field of research has been reviewed fairly extensively in the past (Dooner et al., 1991; van Tunen and MOI, 1991; Gerats and Martin, 1992), in this review we concentrate on the more recent developments in gene isolation and characterization. A review of the genetics of flavonoid biosynthesis in other species was recently covered by Forkmann (1993). The characterization of genetically defined mutations has enabled the order of many reactions in anthocyanin synthesis and their modification to be elucidated. Some reactions have been postulated only on the basis of genetic studies and have not yet been demonstrated in vitro. Chemico-genetic studies have been very important in determining the enzymatic steps involved in anthocyanin biosynthesis and modification. The generation of transposon-tagged mutations and the subsequent cloning of the transposons provided a relatively straightforward means of isolating many genes from maize (Wienand et al., 1990) and snapdragon (Martin et al., 1991). However, a number of genes in the pathway have not been amenable to transposon tagging. Anthocyanin biosynthetic genes have been isolated using a range of methodologies, including protein purification, transposon tagging, differential screening, and polymerase chain reaction (PCR) amplification. Functions of isolated anthocyanin genes can be confirmed by restriction fragment length polymorphism (RFLP) mapping, complementation, or expression in heterologous systems. Reverse genetics has also been used recently to identify gene function; this requires a welldefined pathway to correlate phenotype with gene function. Once a gene has been isolated from one species, it is usually a straightforward task to isolate the homologous gene from other species by using the original clone as a molecular probe.

/pdf/genetics-and-biochemistry-of-anthocyanin-biosynthesis-41091xx7zv.pdf

Genetics and Biochemistry of Anthocyanin Biosynthesis

Genetics and Biochemistry of Ant hocyanin Biosynthesis

A simple and efficient method for direct cloning of PCR products using ddT-tailed vectors.

Flower color is mainly determined by anthocyanins. Rosa hybrida lacks violet to blue flower varieties due to the absence of delphinidin-based anthocyanins, usually the major constituents of violet and blue flowers, because roses do not possess flavonoid 3',5'-hydoxylase (F3'5'H), a key enzyme for delphinidin biosynthesis. Other factors such as the presence of co-pigments and the vacuolar pH also affect flower color. We analyzed the flavonoid composition of hundreds of rose cultivars and measured the pH of their petal juice in order to select hosts of genetic transformation that would be suitable for the exclusive accumulation of delphinidin and the resulting color change toward blue. Expression of the viola F3'5'H gene in some of the selected cultivars resulted in the accumulation of a high percentage of delphinidin (up to 95%) and a novel bluish flower color. For more exclusive and dominant accumulation of delphinidin irrespective of the hosts, we down-regulated the endogenous dihydroflavonol 4-reductase (DFR) gene and overexpressed the Irisxhollandica DFR gene in addition to the viola F3'5'H gene in a rose cultivar. The resultant roses exclusively accumulated delphinidin in the petals, and the flowers had blue hues not achieved by hybridization breeding. Moreover, the ability for exclusive accumulation of delphinidin was inherited by the next generations.

/pdf/engineering-of-the-rose-flavonoid-biosynthetic-pathway-8c2ispj3d3.pdf

Engineering of the Rose Flavonoid Biosynthetic Pathway Successfully Generated Blue-Hued Flowers Accumulating Delphinidin

BLUE and violet flowers generally contain derivatives of delphinidin; red and pink flowers generally contain derivatives of cyanidin or pelargonidin1.Differences in hydroxylation patterns of these three major classes of anthocyanidins are controlled by the cytochrome P450 enzymes flavonoid 3'-hydroxylase and flavonoid 3',5'-hydroxylase. Here we report on the isolation of complementary DNA clones of two different flavonoid 3',5'-hydroxylase genes that are expressed in petunia flowers. Restriction-fragment length polymorphism mapping and complementation of mutant petunia lines showed that the flavonoid 3',5'-hydroxylase genes correspond to the genetic loci Hfl and Hf2.

Timothy A Holton

Papers

Genetics and Biochemistry of Anthocyanin Biosynthesis

Genetics and Biochemistry of Ant hocyanin Biosynthesis

A simple and efficient method for direct cloning of PCR products using ddT-tailed vectors.

Engineering of the Rose Flavonoid Biosynthetic Pathway Successfully Generated Blue-Hued Flowers Accumulating Delphinidin

Cloning and expression of cytochrome p450 genes controlling flower colour