The Green Revolution (GR) of the 1960s saw spectacular increases in cereal crop yields, enabled by widespread adoption of high-yielding semi-dwarf varieties and increased fertilizer use.Semi-dwarfism is caused by mutant wheat Reduced height-1 (Rht-1) and rice semi-dwarf1 (sd1) alleles, respectively, which confer increased harvest index (grain to straw ratio) and reduced yield loss from “lodging” (flattening of crops by wind or rain).However, despite their obvious global food security benefits, the underlying mechanisms via which GR dwarfing alleles actually work remained unknown.This began to change with the molecular discovery of Rht1 (Peng et al., 1999).