Ep type is an important morphological improvement (following dwarf breeding and ideal plant type) that has contributed to breeding super-high yielding, and shows a pleiotropic effect in increasing grain yield and also nitrogen-use efficiency (NUE) in rice. Nevertheless, it remains unclear whether Ep has adverse effects on eating quality and how it affects nitrogen uptake and assimilation. In this study, we developed a pair of near-isogenic lines (NILs) for panicle type (NIL-Ep, NIL-non Ep) in the Liaogeng 5 (LG5) and Akihikari (AKI) backgrounds. Rice plants of the NIL-Ep had higher grain numbers per panicle in the middle to bottom spike positions than plants of the NIL-non Ep. The increased grain number is not only is the key factor leading to increased yield but also is the reason for reduced the eating quality. The content of prolamin and glutelin was significantly higher in NIL-Ep, which resulted in higher hardness and worse viscosity of rice after cooking. In addition, the activity of several essential enzymes catalyzing nitrogen metabolism was higher in the NIL-Ep line grains than in the NIL-non Ep, especially from the mid to late grain filling stage. Based on these results, we conclude that Ep positively regulates grain protein accumulation, primarily through enhancing the activity of enzymes involved in nitrogen assimilation and redistribution during the mid to late grain-filling stage, resulting in excessive accumulation of grain protein and decreased eating quality.
Ep type is an important morphological improvement (following dwarf breeding and ideal plant type) to adapt to super high yield breeding of rice, which shows a pleiotropic effect in increasing grain yield and nitrogen use efficiency (NUE) in rice. Nevertheless, it remains unclear whether Ep has adverse effects on eating quality and its regulatory of increasing nitrogen uptake and assimilation. In this study, we developed a pair of near-isogenic lines (NILs) of dep1 (NIL-Ep, NIL-Non Ep) in the Liaogeng 5 (LG5) and Akihikari (AKI) backgrounds. Here, we report that rice plants NIL-Ep have more grain numbers per panicle in middle to bottom spike positions than plants NIL-non Ep. This part of increased grain not only is the key factor to increase the yield, but also is the reason to reduce the eating quality. The content of prolamin and glutelin in the grain increased significantly, which resulted in higher hardness and worse viscosity of rice after cooking. Additionally, the activity of several essential enzymes catalyzing nitrogen metabolism is higher in the NIL-Ep line than in NIL-non Ep line, especially from the mid to late grain filling stage. Based on these results, we conclude that Ep positively regulates grain protein accumulation primarily through enhance the activity of enzyme enroll nitrogen assimilation and redistribution during the mid to late grain-filling stage, resulting in excessive accumulation of grain protein and decreased the quality of eating.
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