Throughout history, humans have been improving rice.
Do you like rice? Despite the cries for sugar off, sugar-free, and carb restriction, rice is undeniably delicious. Japanese cuisine, often centered around rice as the staple food, seems to have developed to make rice more enjoyable to eat. Looking globally, more than half of the world’s population considers rice (Oryza sativa L.) their primary crop. Cultivation and breeding have been conducted since ancient times, with new varieties being developed every day. While taste is crucial, it’s also thought that labor-saving and breed improvements to cope with population dynamics and global warming will be necessary in the future. Establishing new breeding techniques to achieve better rice is an urgent task.
The potential of new “hybrid rice” combinations.
When we talk about hybrid (HV) rice, it’s worth noting that the rice commonly eaten around the world is mostly HV rice. In Japan, HV rice within the Japonica variety, known for its stickiness, is produced by crossbreeding. In Asia, the Middle East, and Africa, HV within the Indica variety is mainstream. The breeding of intra-species HV is almost exhausted and approaching its limit, necessitating the exploration of new genetic resources, such as mutations. Meanwhile, hybrids between Japonica and Indica varieties exist. These Japonica-Indica HV rices have potential, as each variety has its advantages and often contains genes not found in the other. This is believed to be due to a decrease in diversity after the species diverged, leading to the loss of important genes from each variety. Supporting this, studies suggest that rice diversity decreases with increasing latitude. Crossbreeding Japonica and Indica could undoubtedly produce new varieties with unique traits, but the challenge is high, which is why Japonica-Indica HV rice is not commonly found around us.
The problem lies in the misaligned flowering “clocks”.
The lack of progress in Japonica-Indica HV rice research is mainly due to the mismatch in flowering timing. Rice has a Diurnal Floret Opening Time (DFOT) regulated by the time of day, and this DFOT differs between Japonica and Indica varieties. In HV rice production, Japonica varieties are often used as the male-sterile line (mother) and Indica varieties as the pollen donor (father), requiring synchronization of pistil and pollen timing. Generally, Indica rice shows an earlier DFOT (by an average of 1-3 hours) than Japonica rice. This discrepancy complicates the creation of HV rice and is recognized as a commercial barrier.
The solution lies in genes controlling the “clock”
The approach to align the mismatch is through controlling the DFOT gene in rice, identified as “OsMYB8”. MYB genes are generally known as transcription factors, which don’t code for functional proteins themselves but regulate the expression of other genes. OsMYB8, in particular, regulates rice’s jasmonic acid pathway and controls DFOT. Introducing Indica’s OsMYB8 into Japonica speeds up its DFOT to match that of Indica, facilitating closer timing for pistil and pollen. This increases pollination efficiency, expanding research and commercial production possibilities.
Will the future rice be sticky or fluffy?
By employing shading or low-temperature treatments, it’s possible to synchronize DFOT, and rice produced this way has been reported to yield 15-30% higher. However, these labor-intensive methods are not commercially viable. With the identification of the gene causing DFOT misalignment, research into Japonica-Indica HV rice may advance. What remains intriguing is the characteristics and taste of HV rice: will it be sticky like Japanese rice, fluffy perfect for curry, or a new type altogether? The possibilities are exciting.
Nonetheless, creating “hybrid rice with synchronized DFOT” is the first step in researching hybrid rice.
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