gw2 mutation increases grain width and culm thickness in rice (Oryza sativa L.)

Grain size is one of the most important agricultural traits in rice. To increase grain yield, we screened a large grain mutant from mutants with the ‘Koshihikari’ background. As a result, we obtained a mutant, KEMS39, that has a large grain size and increased yield. Cultivation tests revealed that this mutant had improved lodging resistance with thicker internodes. Next-generation sequencing analysis revealed the presence of a 67 bp deletion in the GW2 mRNA, owing to a mutation in the 3ʹ splice site of the sixth intron of the GW2 gene. To determine whether this mutation was responsible for the larger grain and thicker internodes, we performed gene editing and obtained a mutant with a 7 bp deletion, including this 3ʹ splice site. As this gw2 mutant had large grains and thicker internodes, the causal gene of KEMS39 was determined as GW2. Thicker internodes are attributed to the pleiotropic effect of gw2 mutation. On the basis of these results, we conclude that gw2 mutation has the potential to be an important genetic resource with the ability to achieve a well-balanced and high-yielding effect that simultaneously improves grain productivity and lodging resistance.