Recently, a collaborative effort between researchers from the School of Life Sciences at South China Agricultural University, including Dr. Hai Zhou, Dr. Chuxiong Zhuang, and Professor Zhenlan Liu, along with researchers from the Rice Research Institute of Guangdong Academy of Agricultural Sciences, led by Dr. Junliang Zhao, has unveiled the genes and molecular mechanisms regulating rice flowering time. This significant advancement has been published in the Journal of Plant Biotechnology.
Hybrid rice has significantly increased rice yields. However, traditional intersubspecific hybrid rice, particularly between indica and japonica varieties, has shown limited yield gains. On the other hand, inter-subspecific hybridization between indica and japonica subspecies exhibits higher heterosis, resulting in a further yield increase of 15–30% compared to intra-subspecific hybridization. Nevertheless, the substantial difference in flowering time between indica and japonica rice varieties has led to low hybrid seed production and high seed costs, thereby affecting the economic benefits for farmers and hindering the wider adoption of indica-japonica hybrid rice.
Dr. Hai Zhou and Dr. Chuxiong Zhuang's team has been engaged in molecular mechanism research related to hybrid rice for a long time. They have undertaken studies on photothermal male sterility to address the poor safety of hybridization between two lines and on the flowering time disparity between indica and japonica rice to tackle the low yield issue in inter-subspecific hybrid seed production. Their earlier work on the regulation of rice flowering time by the degree of pectin methylesterification in the cell wall has been regarded as a significant breakthrough in rice flowering research. It revealed, for the first time, the molecular mechanisms regulating rice flowering time, while also proposing effective solutions to the "mismatched flowering time" issue between indica and japonica parents in hybrid seed production, seamlessly integrating fundamental research with practical production needs.
The latest research has discovered that exogenous application of jasmonic acid (JA) can accelerate rice flowering during the day, with the number of flowers positively correlated with JA concentration. Further investigations revealed that by expressing the key JA synthesis gene OsOPR7, knocking out the JA deactivation gene OsHAN1, and suppressing the negative regulators of the JA signaling pathway OsJAZ7 and OsJAZ9, flowering in japonica rice varieties was advanced by 1 hour, 2 hours, 50 minutes, and 1.5 hours, respectively. Molecular mechanism studies indicated that JA synthesis in the leaf sheath increased explosively near flowering, promoting the expression of cell wall remodeling genes, thereby affecting the relaxation degree of the leaf sheath cell wall, causing early water absorption and swelling of the leaf sheath, consequently pushing open the lemma and palea to achieve early flowering.
Yield trait statistics on the aforementioned materials revealed only a slight decrease in yield for the OsHAN1 knockout mutants (which did not affect hybrid rice yield). Importantly, through genetic modification of the japonica male sterile lines to advance their flowering time, thereby aligning with the flowering time of indica male parents, the seed-setting rate of hybrid seeds was increased by 2.86 times compared to before the modification, significantly boosting the yield of indica-japonica hybrid seeds. Four national invention patents have been applied for related achievements.
"Uncovering the genes and molecular mechanisms regulating rice flowering time can provide a theoretical basis and genetic resources for improving and coordinating the flowering times of indica-japonica hybrid rice parents, thereby enhancing seed production," said Dr. Hai Zhou, the corresponding author of the paper. This work offers multiple flowering time regulatory genes for breeders of indica-japonica hybrid rice, elucidates the molecular mechanisms of JA regulation of rice flowering time, and allows for the selective use of different genes in japonica male sterile lines according to specific needs, thereby achieving freedom in indica-japonica hybrid seed production and addressing the bottleneck in indica-japonica hybrid seed production.
For more information about the related paper, please visit: https://doi.org/10.1111/pbi.14343
