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

Authors: CHO, YOUNG - University Of Illinois; BOYD, RYAN - University Of Illinois; REN, YUDONG - Washington University School Of Medicine; LEE, MOON-SUB - University Of Illinois; JONES, SARAH - University Of Illinois; RUIZ-VERA, URSULA - University Of Illinois; McGrath, Justin; MASTER, MICHAEL - University Of Illinois; ORT, DONALD - University Of Illinois

Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2023
Publication Date: 12/4/2023
Citation: Cho, Y.B., Boyd, R.A., Ren, Y., Lee, M., Jones, S.I., Ruiz-Vera, U.M., McGrath, J.M., Master, M.D., Ort, D.R. 2023. Reducing chlorophyll levels in seed-filling stages results in higher seed nitrogen without impacting canopy carbon assimilation. Plant Cell and Environment. 47(1):278-293. https://doi.org/10.1111/pce.14737.
DOI: https://doi.org/10.1111/pce.14737

Interpretive Summary: Although chlorophyll, the pigment that makes leaves green, is necessary for plants to capture light for photosynthesis, previous evidence indicates that leaves produce more chlorophyll than they can use. Chlorophyll production is expensive, and therefore unnecessary production may result in diverting resources away from other limiting factors, in which case reducing chlorophyll production could lead to increased yield or seed quality. To test this, plants were created that reduce their chlorophyll production when sprayed with an alcohol solution. Greater than 60% reduction in leaf chlorophyll production was achieved without reducing yield and seeds had up to 17% increases in nitrogen concentration. The findings suggest that lines with reduced chlorophyll production could produce seeds with more protein with no loss of yield.

Technical Abstract: 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.