# Natural variation in OsMYB8 confers diurnal floret opening time divergence between indica and japonica subspecies

## TL;DR

A gene called OsMYB8 helps explain why indica and japonica rice open their flowers at different times, which could improve hybrid rice breeding.

## Contribution

The study identifies OsMYB8 and OsJAR1 as a regulatory module responsible for natural variation in diurnal floret opening time between rice subspecies.

## Key findings

- OsMYB8 regulates OsJAR1 transcription, affecting cell osmolality and wall remodeling in lodicules.
- Natural variation in the OsMYB8 promoter leads to differential JA-Ile accumulation in indica and japonica.
- Introgression of the indica OsMYB8 haplotype into japonica promotes earlier floret opening.

## Abstract

The inter-subspecific indica-japonica hybrid rice confer potential higher yield than the widely used indica-indica intra-subspecific hybrid rice. Nevertheless, the utilization of this strong heterosis is currently hindered by asynchronous diurnal floret opening time (DFOT) of indica and japonica parental lines. Here, we identify OsMYB8 as a key regulator of rice DFOT. OsMYB8 induces the transcription of JA-Ile synthetase OsJAR1, thereby regulating the expression of genes related to cell osmolality and cell wall remodeling in lodicules to promote floret opening. Natural variations of OsMYB8 promoter contribute to its differential expression, thus differential transcription of OsJAR1 and accumulation of JA-Ile in lodicules of indica and japonica subspecies. Furthermore, introgression of the indica haplotype of OsMYB8 into japonica effectively promotes DFOT in japonica. Our findings reveal an OsMYB8-OsJAR1 module that regulates differential DFOT in indica and japonica, and provide a strategy for breeding early DFOT japonica to facilitate breeding of indica-japonica hybrids.

Florets of indica rice open earlier than japonica rice, hindering utilization of the cross subspecies heterosis. Here, the authors show that an OsMYB8-OsJAR1 module regulates diurnal floret opening time divergences between the two subspecies.