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Rice Can Drown Too

The mechanism of rice submergence tolerance.

Rice is a semi-aquatic plant, however the seedlings will die if they are submerged completely under water and oxygen is depleted.

Researchers from Academia Sinica’s Agricultural Biotechnology Research Center and Institute of Biological Chemistry in Taiwan, have investigated rice oxygen sensing mechanism and its submergence response.

Some rice varieties possess an important transcription factor, called SUB1A-1, and can withstand up to two weeks of submergence. This anti-submergence gene, SUB1A-1, inhibits rice growth during flooding to conserve energy and increase its survival. This is a similar strategy to how bears hibernate during winter. However, it is unclear how SUB1A-1 activates the anti-submergence responses in rice.

The team discovered SUB1A-1 will activate two transcription factors, ERF66 and ERF67, which turn on the submergence response mechanism in rice to enhance survival.

More importantly, the research team found that ERF66 and ERF67 possess a special amino acid sequence (N-degron) that can function as an oxygen sensor in rice.

In normoxia environments, the N-degron is oxidised followed by protein degradation via ubiquitin-proteasome system. As a result, no submergence response is activated in rice when oxygen is available.

Only when rice is drowned and oxygen is depleted, ERF66 and ERF67 are not degraded. The stabilised ERF66 and ERF67 will then activate various downstream genes to respond to submergence.

Based on this finding, a SUB1A-1/ERF66/ERF67 signal cascade system for hypoxia sensing and submergence-resistance mechanism was proposed.

Climate change has inflicted typhoons and heavy rainfall into a frequent occurrence, which greatly reduced rice production in Taiwan and severely threatens food security.

Their findings extend current understanding about how rice cultivars withstand submergence and can help improve the hardiness of other crops in the future.

Their results were published in Proceedings of the National Academy of Sciences of the United States. [APBN]