Analysis of Heavy Ion Beam Mutants in Brachypodium distachyon

Brachypodium distachyon is a model plant for cereal and energy crops, and is the first species with a sequenced genome in grass subfamily Pooideae. To understand the molecular mechanisms underlying crop quality and productivity, we have initiated studies of "Heavy Ion Beam" (HIB) mutants in B. distachyon. Heavy ion beams are accelerated ions produced by an accelerator such as a cyclotron or synchrotron, and effectively induce DNA double-strand breaks than other mutagenic techniques. We irradiated dry seeds of the genome-sequenced accession, Bd21, with carbon ions (22.5 keV / μm LET) at a dose that ranged from 100 to 300 Gy in the RIKEN RI-beam factory. Germination and survival rates of HIB irradiated M₁ seeds decreased with increasing HIB dose. The progeny of M₁ seeds showed a variety of phenotypes, and were screened in the M₃ generation based on visible phenotypic differences between mutants and wild type. We measured morphological phenotypes carefully such as leaf thickness, leaf width, leaf blade length and plant height. For Examples, we screened some mutants showing narrower and longer leaf blade, dwarf phenotype and longer spikelet with increased number of florets. To identify the causal gene of these screened HIB mutants, whole genome resequencing is progressing in our laboratory.