Comparative genomics of cereals

Abstract

Cereals such as wheat, barley, maize, sorghum, millet and rice belong to the grass family and comprise some of the most important crops for human and animal nutrition. Comparative genomic studies in cereals have been pioneering the field of plant comparative genomics in the past decade. The first comparative studies were performed at the genetic map level. They have revealed a very good conservation of the order (colinearity) of molecular markers and of QTL for agronomic traits along the chromosomes thereby establishing evolutionary relationships between the cereal genomes. For this reason and because of its small size, rice was promoted as a model and was chosen to be the first cereal genome sequenced. Further, the development of large EST collections and the first inter- and intra-specific comparative studies of BAC sequences from maize, sorghum, rice, wheat and barley have increased the resolution of comparative analyses and have shown that a number of rearrangements disrupting microcolinearity have occurred during the evolution of the cereal genomes in the past 50-70 million years. This chapter reviews comparative studies that have been performed at the macro- and micro-levels in cereals and discusses what was learned about the mechanisms underlying genome evolution in these important crop species. It describes how this knowledge can be applied to support gene discovery and cereal crop improvement and presents the opportunities that will be available within the next few years as the sequencing of several cereal genomes in addition to rice will be completed.