Organellar Genomes in Barley

Abstract

Similar to other higher plants, barley (Hordeum vulgare) contains the following three cell organelles that possess their own genomes: nucleus, mitochondrion, and chloroplast. In this chapter, the genome structures, genetic content, and functions of two cytoplasmic organelles, i.e., mitochondrion and chloroplast, in barley are discussed. The barley mitochondrial genome (mt genome) is 525,599 bp in size, which is 73 kb larger than that of wheat, and the gene content is well conserved among grass species; notably, the contents of intact protein-coding genes in barley are the same as those in wheat. However, the mt genome structure is markedly different among grass species, and rearrangements and fragmentations of homologous regions prevent the reconfiguration of evolutionary processes, even in the same Triticeae lineage, which includes barley and wheat. However, the genome structure and gene content of chloroplast genome (cp genome) are highly conserved among grass species. The cp genome in barley is 136,462 bp in size, and the quadripartite structures that are common in the cp genome of higher plants are conserved. Most sequences are collinear between wheat and barley, and the gene content and gene order in barley are identical to those in wheat. Chloroplasts and mitochondria are essential organelles, and the genes encoded in both organellar genomes are indispensable for plant cell survival. Several genetic interactions among the cell organelles, nucleus, mitochondrion, and chloroplast occur within a cell. In this chapter, these genetic interactions and outcomes, including cytoplasmic male sterility (CMS) and chloroplast dysfunction, are reviewed. These phenomena are interesting and important for the understanding of the physiological function of both cytoplasmic organelles and their potential use in plant breeding. We have only recently begun to understand these genetic interactions due to the publication of the complete genomes of the nucleus, mitochondrion, and chloroplast in barley.