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The researchers found evidence suggesting that the pungency, or "heat," of the hot pepper originated through the evolution of new genes by duplication of existing genes and changes in gene expression after the peppers evolved into species. (Credit: erik forsberg/Flickr)

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Hot pepper genome reveals its spicy evolution

The hot pepper genome is 3.5-fold larger than that of the tomato, its closest relative, and blocks of genes appear in much the same chromosomal position, report researchers.

The newly sequenced reference genome sheds light on the biology of the pepper’s hallmark pungency, or spiciness, as well as its fruit-ripening and disease-resistance mechanisms.

It also reveals new information crucial for improving the horticultural, nutritional, and medicinal qualities of these peppers, whose annual global production has grown more than 40-fold during the past two decades and now exceeds $14.4 billion.

Highlights from the sequencing effort appear early online in the journal Nature Genetics.

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“The pepper genome is one of the largest genomes assembled to date,” says plant scientist Allen Van Deynze, director of research at the University of California, Davis, Seed Biotechnology Center and a co-author on the study.

“The quality of this genome assembly and linkage to the high-density genetic map for peppers makes the genes and genome immediately available to the genetics community,” he says.

Hot pepper varieties

Hot peppers, one of the oldest domesticated crops in the Western Hemisphere, are members of the Solanaceae plant family and thus cousins to an extensive group of plants including potato, tomato, eggplant, petunia, and tobacco.

The hot-pepper plants are popular ornamentals and produce fruits that are major vegetables in most global cuisines, as well as rich sources of vitamins and nutrients, pharmaceuticals, natural coloring agents, cosmetics, and defense repellants.

The researchers sequenced a hot pepper landrace, or domesticated variety, from the Mexican state of Morelos. The variety, known as Criolo de Morelos 334, has consistently exhibited high levels of disease resistance and has been extensively used in hot-pepper research and breeding.

The research team also provided sequencing data for the Perennial and Dempsey cultivated pepper varieties and for the related habanero pepper species (Capsicum chinense).

‘Heat’ and other benefits

The sequencing also uncovered evidence suggesting that the pungency, or “heat,” of the hot pepper originated through the evolution of new genes by duplication of existing genes and changes in gene expression after the peppers evolved into species.

It was already known that pepper pungency was caused by the accumulation of naturally occurring chemicals called capsaicinoids, unique to the Capsicum genus.

More than 22 of these “heat”-producing compounds have been isolated from peppers, and many have been shown to have human health benefits, including inhibition of tumor growth for certain cancers, pain relief for arthritis, appetite suppression, and weight-loss promotion.

Information from this sequencing project will help scientists better understand how these compounds are synthesized in the pepper plant. It also establishes the pepper as a valuable model for exploring, in general, the evolution of plants’ organic compounds—beyond those directly involved in growth, development, and reproduction.

“The fine genetic mapping of pepper promises cost-effective and early screening for valuable agricultural traits,” says co-author Ryan W. Kim of the UC Davis Genome Center.

The Korean government’s Rural Development Administration and National Research Foundation funded the study, as well as the private companies Hortigenetics, Monsanto, Riijk Zwaan, Syngenta, Semilla Fito, Sakata Seed, Enza Zaden, Nunhems, and Takii.

Source: UC Davis

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