Abstract
Grain quality is a critical component of high-yielding varieties to ensure acceptance by an ever-increasing population and living standards. During the past years, several photorespiration bypasses have been introduced into C3 plants, among which our GOC and GCGT bypasses exhibit increased photosynthesis and yield in rice. However, to the best of our knowledge, there are still no reports referring to effects of the bypasses on grain quality. Thus, the objective of this study is to determine the effect of GOC and GCGT bypasses on grain quality, and the mechanism of how photorespiratory bypasses affect grain quality was also investigated. Compared with the WT of Zhonghua 11, GOC4 and GCGT20 plants had higher nutritional quality and cooking quality as grain protein content was significantly increased by 11.27% and 14.97%, and alkali spreading value was significantly increased by 7.6% and 4.63%, respectively, whereas appearance quality appears to be negatively affected since the chalky rice rate was increased by 32.6% and 68%, respectively. Analyses also demonstrated that the changes in grain quality may result from the increased total nitrogen and constrained carbohydrate transport in the transgenic plants. Altogether, the results not only suggest that the increased photosynthesis and yield by introducing the photorespiratory bypasses can significantly affect grain quality parameters for rice, either positively or negatively, but also imply that the coordination of source–sink transport may play important roles in grain quality formation for high-yielding crops via increased photosynthetic efficiency.
Highlights
Rice (Oryza sativa L.) is a staple food feeding more than half of the population in the world
The results showed that there were no significant differences in the brown rice rate and milled rice rate between GOC4, GCGT20, and WT rice grains (Figure 1A,B)
The head milled rice rate was shown to be decreased in GOC4 and GCGT20 relative to WT (Figure 1C), meaning that milling quality of the transgenic grains was decreased to some extent
Summary
Rice (Oryza sativa L.) is a staple food feeding more than half of the population in the world. With the global population continuing to rise, there is a great need to increase crop yield. Improvement of photosynthetic efficiency is regarded as a major feasible option to increase crop yield potential [3]. Mitigating the negative effects of photorespiration remains an important bioengineering target to improve the photosynthesis and yields of crops to meet demands of growing population [4,6]. The GOC bypass completely oxidizes glycolate into CO2, which was catalyzed by three rice-selforiginating enzymes, i.e., glycolate oxidase (OsGLO3), oxalate oxidase (OsOXO3), and catalase (OsCAT), while the GCGT bypass consists of four enzymes including Oryza sativa glycolate oxidase (OsGLO1) and Escherichia coli catalase (EcCAT), glyoxylate carboligase (EcGCL), and tartronic semialdehyde reductase (EcTSR), which can redirect 75% of carbon from glycolate metabolism to the Calvin cycle. In order to improve both quality and crop yields, it is necessary to understand the key quality traits of crops, so that they can be selected in the breeding plan and controlled by proper crop managements
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