Reducing chlorophyll levels in seed‐filling stages results in higher seed nitrogen without impacting canopy carbon assimilation

Chlorophyll is the major light‐absorbing pigment for plant photosynthesis. While evolution has been selected for high chlorophyll content in leaves, previous work suggests that domesticated crops grown in modern high‐density agricultural environments overinvest in chlorophyll production, thereby lowering light use and nitrogen use efficiency. To investigate the potential benefits of reducing chlorophyll levels, we created ethanol‐inducible RNAi tobacco mutants that suppress Mg‐chelatase subunit I (CHLI) with small RNA within 3 h of induction and reduce chlorophyll within 5 days in field conditions. We initiated chlorophyll reduction later in plant development to avoid the highly sensitive seedling stage and to allow young plants to have full green leaves to maximise light interception before canopy formation. This study demonstrated that leaf chlorophyll reduction >60% during seed‐filling stages increased tobacco seed nitrogen concentration by as much as 17% while canopy photosynthesis, biomass and seed yields were maintained. These results indicate that time‐specific reduction of chlorophyll could be a novel strategy that decouples the inverse relationship between yield and seed nitrogen by utilising saved nitrogen from the reduction of chlorophyll while maintaining full carbon assimilation capacity. Summary statement Reducing chlorophyll levels in tobacco plants during seed filling stages, without compromising canopy carbon assimilation, increased seed nitrogen concentration by up to 17%, suggesting a potential strategy to improve yield and seed nitrogen content simultaneously.