Describing and Cloning Root Mutants in Barley

Despite the importance of mutants in plant biology investigations and plant breeding, only a limited number of root mutants have been described in crop species. Recently, the interest in mutant collections has increased due to the availability of new genomics-assisted mapping and cloning approaches (e.g. mapping by sequencing) enabling the exploitation of mutant collections in a forward-genetics fashion. In this context, we performed a screening of a barley mutant population (cv. Morex background) formerly produced for TILLING purposes (Talamè et al. 2008,Plant Biotech J. 6:477-485), to identify and clone root morphology mutants. By means of a paper-roll method, 3,071 M5 mutant families were phenotyped at the seedling stage and over 60 putative root mutants were identified. Mutants were grouped in three categories: root growth rate/length (short and long, 77%), root morphology (coiling, geotropic, etc., 15%) and root hairs (hairless, shorthairs, etc., 8%). Four mutants were utilized in experimental crosses and their Mendelian inheritance confirmed. A SNP array-based bulk-segregant analysis applied to the segregating F2 assembled from the crosses between the mutants and the wild type allowed us to quickly map the mutations at cM-range interval. NGS-based approaches are being tested both on phenotypic bulks and single mutant lines in order to streamline the process of linking a mutant with the underlying gene, thus making our population a useful resource for functional genomics in cereals. In two cases, plausible candidates have been identified and are being validated.