A mutation of GRAS SCL14 gene confers moderate sensitivity to the herbicide bentazon in soybean

Bentazon is an effective post-emergence herbicide in soybean. A loss of function of cytochrome P450 hydroxylase encoded by a recessive gene, bzn-1 (Glyma.16G149300), is known to confer high sensitivity to bentazon, while there is natural variation causing moderate sensitivity to bentazon that cannot be accounted for by bzn-1. Here, we identified another recessive gene, bzn-2, that confers the moderate sensitivity to bentazon. The candidate region of bzn-2 was narrowed down to 92 kb on chromosome 11 by positional cloning using recombinant inbred lines from a cross between bentazon-tolerant and moderately sensitive varieties. Sequence comparison of these varieties for 12 genes located in the candidate region revealed that the moderately sensitive variety had a single-base substitution that caused a stop codon in the coding region of Glyma.11G138300. This gene encodes GRAS SCL14 (GRAS: GIBBERELLIN ACID INSENSITIVE, REPRESSOR of GA1, and SCARECROW; SCL: SCARECROW-like 14), a class II TGA transcription factor. Screening of germplasms by an amplification-refractory mutation system (ARMS) marker clearly distinguished the accessions that are moderately sensitive to bentazon. Three independent EMS mutants of Glyma.11G138300 were moderately sensitive to bentazon, strongly supporting Glyma.11G138300 as the causal gene for bzn-2. The low expression of mutated Glyma.11G138300 reduced expression of Glyma.16G149300, encoding the P450, resulting in a moderately sensitive phenotype. To the best of our knowledge, this is the first report demonstrating that natural variation in the GRAS gene family confers herbicide tolerance. Our findings are useful for understanding the mechanism of detoxification and for selection of bentazon tolerance through breeding.