Barley: emergence as a new research material of crop science.

The completion of genome sequencing, advances in a wide range of analytic technologies, greater research platforms and the emergence of bioinformatics procedures, as well as the development of related resources, have contributed to improvements in the quality of research not only in model species but also in crop plants and livestock. Sustainable agricultural production is an urgent issue in the context of global climate change and food security (Brown and Funk 2008, Turner et al. 2009). In order to address this issue, the integration of a broad spectrum of analytical tools and resources and an understanding of genetic mechanisms for agriculturally important traits is needed (Yamamoto et al. 2009, Mochida and Shinozaki 2010). Several essential features of barley (Hordeum vulgare L.) contribute to the broad utilization of this crop in genetic studies. These features include (i) the crop’s diploid nature with a high degree of inbreeding; (ii) the low chromosome number (2n = 14) with large size; (iii) the ease of cross-breeding; and (iv) the ease of cultivation in a wide range of climatic conditions. Cultivated barley, which ranks fourth among cereals with respect to worldwide production, is also well known as an extensively studied plant species in the field of genetics. Regarding its geographic adaptability, barley is particularly noted for its tolerance to cold, drought, alkalinity and salinity. In recent years, to address its huge genome size ( 5,000 Mb), research resources essential for barley genomic studies have been developed, including a large number of expressed sequence tags (ESTs). These have been widely used for barley genome analyses such as DNA marker generation and the construction of microarrays. Recent innovations in sequencing technology, which allow for working on a massive scale by genotyping thousands of single nucleotide polymorphisms (SNPs) on a genome-wide scale, have enabled us to dissect many genetically and biologically agronomically important complex traits. Advanced mapping populations, including chromosome segment substitution lines (CSSLs), have worked as the engines of genetic dissection of quantitative trait loci (QTLs) (Fukuoka et al. 2010). Resources for barley functional genomics have improved over the last decade, and several high-density genetic maps utilizing various types of molecular markers have been constructed (Close et al. 2009, Schulte et al. 2009). Several CSSLs have also been developed, and these are being used for various QTL discovery and related analyses in barley (e.g. Hori et al. 2005). Furthermore, >370,000 barley germplasms are preserved as ex situ collections in representative genebanks, including Okayama University (http://www .shigen.nig.ac.jp/barley/), and worldwide. In this special issue on barley in Plant and Cell Physiology, we discuss the historic advantages of barley as a genetic research material, as well as crop improvements, and briefly outline recent achievements in the establishment of genomic infrastructure that have enabled us to examine the characteristic traits of barley and/or to compare findings with other plant species such as Arabidopsis, rice, maize and soybean. Sato et al. (pp. 728–737) provided new barley research resources in the form of a doubled haploid population derived from the cross between the malting variety ‘Haruna Nijo’ and the Japanese landrace ‘Akashinriki,’ as well as 35 CSSL introgressions from ‘Akashinriki’ on a ‘Haruna Nijo’ background. Several genes controlling barley flower and inflorescence morphology have been isolated by means of map-based cloning technology, including the genes encoding the six-rowed spike (Komatsuda et al. 2007) and naked caryopsis (Taketa et al. 2008). These morphological characteristics and the nonbrittleness (grain shattering) of barley are well-known characteristic traits of domesticated barley, and a model of the barley domestication process has been developed based on archeological evidence of these characteristics (Zohary and Hopf 2000). Sakuma et al. (pp. 738–749) provides an overview of the disarticulation systems and inflorescence characteristics, along with the genes underlying these traits, occurring in the Triticeae tribe. In spite of its large genome, barley is recognized as a good genomic model of the Triticeae tribe, which includes cultivated wheat (einkorn, durum and bread wheats), rye and their respective wild relatives (Schulte et al. 2009). The evolution of the polyploid wheats is distinctive in that domestication, natural hybridization and allopolyploid speciation have significant impacts on their diversification. In this special issue, Matsuoka (pp. 750–764) outlines the phylogenetic relationship between cultivated wheats and their wild relatives and provides an overview of the recent progress and remaining questions in our