Kernels of truth: Researchers sequence the maize genome

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ST. LOUIS, Mo. — The completion of a high-quality sequence of the maize (corn) genome is in the cover story of the Nov. 20 issue of Science. This new genome sequence reports the sequence of genes in maizeand provides a detailed physical map of the maize genome.

This map identifies the order in which genesare located along each of maize’s 10 chromosomes and the physical distances between those genes.

Additional information provided by the new maize genome sequence includes the locations on chromosomes of interesting, repeated sections of DNA (called centromeres) that are responsible for the faithful inheritance of those chromosomes by daughter cells during cell division.

This new genome sequence represents a major watershed in genetics because it promises to advance basic research of maize and other grains and help scientists and breeders improve maize crops, which are economically important and serve as globally important sources of food, fuel and fiber.

Research team

The new maize sequence was produced by a consortium of researchers that was led by the Genome Sequencing Center at Washington University in St. Louis, Mo., and included the University of Arizona, Iowa State University and Cold Spring Harbor Laboratory in New York.

Real-world applications

Accompanying the announcement of the new maize genome sequence is a “Perspective” on the sequence.

The same issue also announces the results of two other NPGI-funded studies that were enabled by the new maize sequence.

One of these studies produced a so-called HapMap of the maize genome, which describes the genetic differences between various strains of maize that are currently bred around the world.

This resource will help researchers identify the genes that control various maize traits.

The other NPGI-funded study that also appears issue builds on the new maize genome sequence by identifying a surprisingly widespread biological process that determines the level of expression ofcertain genes present in hybrid strains of maize.

The issue also reports on the sequencing by a Mexican consortium led by Luis Herrera-Estella of CINVESTAV, Irapuato, Mexico of the popcorn variety Palomero toluqueno, which is bred in central Mexico.

Comparisons between Palomero toluqueno and the NSF-funded genome sequence, which is from a maize strain that is inbred in mid-western regions of the U.S., reveals important clues about how maize has been domesticated over the last 10,000 years and highlights the importance of biodiversity.

Significance

This new maize sequence provides significant refinements over the draft sequence that was announced in February 2008. These refinements include the elimination of redundancy and improvements in the ordering and orientation of chromosomal segments.

Because maize has served as a model plant for basic genetics research for the last 100 years, the completion of its genome sequence has important implications for basic research — as already evidenced by the immediate publication of the two companion papers in Science.

In addition, the Nov. 20 issue of PLoS Genetics features an editorial on the new maize sequence and 10 more companion studies — each of which either provides background information on the development of the maize sequence or uses the new maize sequence to produce additional insights into maize genetics.

In addition to advancing research on maize, the maize genome sequence is also expected to advance other cereal genome sequencing projects, such as those for wheat and barley.

A daunting task

The maize sequencing project, which was initiated in 2005, is a notable achievement because it was completely quickly and because the maize genome is among the most challenging genomes sequenced to date.

The complexityof the maize genome is partly due to its size: with 2.5 billion base pairs covering 10 chromosomes, the maize genome is almost as big as the human genome.

The complexity of the maize genome is also partly due to the fact that about 85 percent of its DNA is composed of transposable elements — segments of DNA that can move between locations.

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