Rice is one of the most important crops worldwide, and half of the world's population regards it as a major staple every day. Continuously improving rice yield is necessary. Traditional upland rice generally exhibits insufficient grains resulting from abnormal endosperm development compared to paddy rice. However, the underlying molecular mechanism of this trait is poorly understood. 

In a study published in Journal of Integrative Plant Biology, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences identified and cloned a UDP-glucosyltransferase gene, EDR1 (Endosperm Development in Rice), which was responsible for differential endosperm development between upland rice and paddy rice. 

Yanzhinuo (YZN), an upland rice variety, was used as the donor parent, which exhibited abnormal endosperm development and poor grain quality. Yundao1 (YD1), a paddy rice variety, was used as the recurrent parent and it exhibited normal endosperm. 

Natural variations in EDR1 significantly reduced the UDP-glucosyltransferase activity of upland rice compared to paddy rice, resulting in abnormal endosperm development in the near-isogenic line (NIL), accompanied by insufficient grains and changes in grain quality. 

By analyzing the distribution of the two alleles EDR1 of YZN and YD1 among diverse paddy rice and upland rice varieties, the researchers discovered that EDR1 was conserved in upland rice, but segregated in paddy rice. 

Grain quality analysis showed a significant increase in grain chalkiness but a decrease in the transparency and protein content of YZN seeds. The upland rice variety harboring EDR1 of YZN showed high chalkiness, while the paddy rice variety harboring EDR1 of YD 1 exhibited low chalkiness. 

"The results indicate that the UDP-glucosyltransferase gene EDR1 plays an important role in regulating endosperm development in upland rice and paddy rice, thereby influencing grain quality in rice," said XU Peng, principal investigator of the study.