Lateral Branching Oxidoreductase specificity for strigolactone branching inhibition in barley

Strigolactone (SL) mutants display a range phenotypes, such as increased branching, reduced stature and a loss of SLs exuded from roots into soil. SL biosynthesis is complex and divergent between plant species. Recently, mutants defective in specific SL biosynthesis genes have shown a loss of exuded SLs, but no obvious change in branching (tillering). This means that functional specification may exist between certain SL sub-types. It has been suggested that the LATERAL BRANCHING OXIDOREDUCTASE (LBO) enzyme acts in a sub-pathway of SLs that is specific for branching. Here we report that barley plants mutants in hvlbo have increased tillering, but normal production of SLs detected in roots and root exudates. This finding supports the idea that SLs have functional or tissue-specific differences and that the LBO pathway has specificity for bud outgrowth rather than exudates.