SYL3-k increases style length and yield of F1 seeds via enhancement of endogenous GA4 content in Oryza sativa L. pistils

Abstract

SYL3-k allele increases the outcrossing rate of male sterile line and the yield of hybrid F₁ seeds via enhancement of endogenous GA₄ content in Oryza sativa L. pistils. The change in style length might be an adaptation of rice cultivation from south to north in the northern hemisphere. The style length (SYL) in rice is one of the major factors influencing the stigma exertion, which affects the outcross rate of male sterile line and the yield of hybrid F₁ seeds. However, the biological mechanisms underlying SYL elongation remain elusive. Here, we report a map-based cloning and characterisation of the allele qSYL3-k. The qSYL3-k allele encodes a MADS-box family transcription factor, and it is expressed in various rice organs. The qSYL3-k allele increases SYL via the elongation of cell length in the style, which is associated with a higher GA₄ content in the pistil. The expression level of OsGA3ox2 in pistils with qSYL3-k alleles is significantly higher than that in pistils with qSYL3-n allele on the same genome background of Nipponbare. The yield of F₁ seeds harvested from plants with 7001S^SYL3-k alleles was 16% higher than that from plants with 7001S^SYL3-n allele. The sequence data at the qSYL3 locus in 136 accessions showed that alleles containing the haplotypes qSYL3^AA, qSYL3^AG, and qSYL3^GA increased SYL, whereas those containing the haplotype qSYL3^GG decreased it. The frequency of the haplotype qSYL3^GG increases gradually from the south to north in the northern hemisphere. These findings will facilitate improvement in SYL and yield of F₁ seeds henceforward.