Brachypodium distachyon. A New Model System for Functional Genomics in Grasses

Abstract

A new model for grass functional genomics is described based on Brachypodium distachyon, which in the evolution of the Pooideae diverged just prior to the clade of "core pooid" genera that contain the majority of important temperate cereals and forage grasses. Diploid ecotypes of B. distachyon (2n = 10) have five easily distinguishable chromosomes that display high levels of chiasma formation at meiosis. The B. distachyon nuclear genome was indistinguishable in size from that of Arabidopsis, making it the simplest genome described in grasses to date. B. distachyon is a self-fertile, inbreeding annual with a life cycle of less than 4 months. These features, coupled with its small size (approximately 20 cm at maturity), lack of seed-head shatter, and undemanding growth requirements should make it amenable to high-throughput genetics and mutant screens. Immature embryos exhibited a high capacity for plant regeneration via somatic embryogenesis. Regenerated plants display very low levels of albinism and have normal fertility. A simple transformation system has been developed based on microprojectile bombardment of embryogenic callus and hygromycin selection. Selected B. distachyon ecotypes were resistant to all tested cereal-adapted Blumeria graminis species and cereal brown rusts (Puccinia reconditia). In contrast, different ecotypes displayed resistance or disease symptoms following challenge with the rice blast pathogen (Magnaporthe grisea) and wheat/barley yellow stripe rusts (Puccinia striformis). Despite its small stature, B. distachyon has large seeds that should prove useful for studies on grain filling. Such biological characteristics represent important traits for study in temperate cereals.

Cytogenetic evidence of nucleolar dominance in allotetraploid species ofBrachypodium

“…Interest in the genus increased when initial molecular study (Shi et al 1993;Catalan and Olmstead 2000) revealed its close phylogenetic proximity with agronomically important cereals such as wheat and barley. Additionally, microdensitometric and flow cytometry measurements proved Brachypodium species to have very low nuclear DNA content (Draper et al 2001;Bennett and Leitch 2005).…”

“…As a result, the inbreeding annual weedy grass Brachypodium distachyon has been proposed as a species of choice for comparative genomic studies of its less tractable but agronomically important relatives (Draper et al 2001;Jenkins et al 2003Jenkins et al , 2005. The potential of B. distachyon as a model plant has been supported by studies demonstrating its high capacity for cell culture, transformation, and regeneration (Bablak et al 1995;Christiansen et al 2005), efficiency in mutagenesis procedures (Draper et al 2001;Engvild 2005), and usefulness in studies of plant-pathogen interactions (Routledge et al 2004;Allwood et al 2006) as well as functional analyses of genes (Olsen et al 2006).…”

“…The collected accessions of B. distachyon exhibit variation in somatic chromosome number ranging from 10 to 30 (Robertson 1981;Draper et al 2001). The ecotypes with 20 and 30 chromosomes were initially considered to be autotetraploids and autohexaploids, respectively, that originated from a diploid form with a chromosome number of 10 by simple multiplications of the same chromosome set (Robertson 1981).…”

The effects of chronic radiation of gamma ray on protein expression and oxidative stress inBrachypodium distachyon

“…Th erefore, a model system for forage grasses and cereal crops was required to provide more general genomic data for grasses, which may aid in the identifi cation of genes of agronomic interest (Keller and Feuillet 2000). Brachypodium distachyon , a member of the Pooideae subfamily, is a wild annual grass that possesses several traits that make it an ideal model organism for the study of temperate cereals, including small size, rapid generation time, a small genome, diploid accessions, and simple growth requirements (Draper et al 2001). Highly effi cient transformation methods have been developed, and B. distachyon germplasm has been collected for morphological and cytological analyses (Scoles et al 2009).…”

Spatial Distribution of Epigenetic Modifications in Brachypodium distachyon Embryos during Seed Maturation and Germination

“…The Brachypodium embryo is almost identical to the embryos of barley and wheat anatomically. This wild grass is a model for temperate cereals and forage grasses due to its numerous valuable features, such as its small stature and genome size and short life cycle, which make it suitable for laboratory research [28]–[30]. Recently, Barrero et al [24] proposed Brachypodium as an ideal model for studies of grain dormancy in grasses and recommended that it be used to identify new strategies for increasing grain dormancy in crop species.…”