Would reducing chlorophyll content result in a higher photosynthesis nitrogen use efficiency in crops?
Decreasing antenna size is regarded as a potential strategy to improve photosynthesis for higher yield potential. Reducing chlorophyll content has been used as a strategy to decrease antenna size. One of the commonly cited benefits of this strategy has been its ability to improve crop nitrogen use efficiency; however, field evidence for this so far is limited. Here we used a mutant, p35s-Ami-YGL1, which has a lower chlorophyll content and also lower antenna size, to study the impacts of modifying leaf chlorophyll content on tissue nitrogen content and nitrogen use efficiency of plants. We show that the nitrogen contents for different tissues, including the seed tissue, on a weight basis were increased in p35s-Ami-YGL1, together with a decrease in C: N. Concurrently, we found that tissue carbon content decreased, while the content of chlorophyll precursors increased. These results suggest that the observed increase in tissue nitrogen content in Ami-YGL1 does not reflect an increase in plant nitrogen absorption or use efficiency, rather it is a result of stunted carbon fixation capacity of plants. The observed increase in seed nitrogen content in Ami-YGL1 suggests a potential strategy to increase seed nitrogen content in crops. Overall design: The p35s-Ami-YGL1 mutant plants were generated with RNAi technology as described earlier (Mao et al., 2023). We used three homozygote transgenic lines (line 1, 7 and 8) during this study.  Rice (Oryza sativa spp japonica cv Nipponbare) and p35s-Ami-YGL1 were grown in the experimental station of the Shanghai Institute of Plant Physiology and Ecology (121°8'1.33?E, 30°56'26.73?N). During the growth period in 2021 or 2022, the rice was transplanted into the well-fertilized field in a 7×7 layout (25cm ×25 cm) and for each line. To avoid boundary effects, plants belong to the boundary lines were excluded in the measurement. The experiments were done in two years at different field sites (2019, 2021).   At the same time, we also carried out relevant measurements in the plant greenhouse. The greenhouse was subjected to an alternating light/dark cycle (12 hours of light and 12 hours of darkness), with a light intensity of approximately 400 µmol m-2 s-1 and the temperature was set at around 28 oC. Strategic Priority Research Program of the Chinese Academy of Sciences (grant number: XDB37020104) National Research and Development Program of Ministry of Science and Technology of China (2019YFA0904600; 2020YFA0907600) the general program of National Science Foundation of China (31870214, 31970378)