Email: komura.shouya.48p@st.kyoto-u.ac.jp

Reduction of culm length is one of the most essential traits in wheat breeding to avoid lodging, which causes severe damage to the yield and quality. In this study, we irradiated the Japanese wheat variety 'Chikugoizumi' with gamma-rays and obtained a mutant with a shorter culm length than the wild type. To determine the genomic regions responsible for the mutant phenotype, we applied whole genome sequencing to the mutant and wild type.

Since gamma radiation often causes structural variants such as deletions, the depth of coverage across the genome was estimated to detect deletions. By comparing the depth-of-coverage between wild-type and mutants, we detected a deletion of 0–36 Mbp region of chromosome 2B and a duplication of 636–713 Mbp region of chromosome 5A. In addition, we confirmed that the duplication region of chromosome 5A was translocated to the end of the deleted chromosome 2B by fluorescence in situ hybridization (FISH).

Segregation analysis using the F2 population generated from a cross between the mutant and the wild-type showed that the chromosome 2B-5A translocation was significantly associated with the reduction of culm length. The translocation region contained two previously reported culm length-related genes, Q (TraesCS5A03G1116700) and Rht12 (TraesCS5A03G1269600). Since Rht12 encodes the gibberellic acid (GA) 2-oxidase protein, to determine whether the reduction in culm length was caused by a gibberellin-related response, we treated the mutant and the wild type with exogenous GA3.

The GA3 treatment increased the culm length in both the wild-type and the mutant. In particular, the increase in the short culm mutant was remarkable. The results suggested that exogenous GA3 compensated for endogenous GAs inactivated by Rht12 and that the amount of inactivated GA is higher in the mutants.

Furthermore, even after elongation by exogenous GA3, the wild type exhibited longer culm length than the mutant indicating that there is a factor causing culm length reduction independent of the GA pathway. Q has been reported to reduce culm length in a GA-insensitive manner. Therefore, it was inferred that both Q and Rht12 caused the reduction of culm length through increased copy number resulting from the chromosome 5A translocation.

Our results would provide useful resources for improving plant height. This study was supported by MAFF Commissioned project study on "Smart-breeding System for Innovative Agriculture [DIT1002]".