The dependency of red Rubisco on its cognate activase for enhancing plant photosynthesis and growth

Laura H. Gunn, Elena Martin Avila, Rosemary Birch, Spencer M. Whitney*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    38 Citations (Scopus)


    Plant photosynthesis and growth are often limited by the activity of the CO2-fixing enzyme Rubisco. The broad kinetic diversity of Rubisco in nature is accompanied by differences in the composition and compatibility of the ancillary proteins needed for its folding, assembly, and metabolic regulation. Variations in the protein folding needs of catalytically efficient red algae Rubisco prevent their production in plants. Here, we show this impediment does not extend to Rubisco from Rhodobacter sphaeroides (RsRubisco) - a redtype Rubisco able to assemble in plant chloroplasts. In transplastomic tobRsLS lines expressing a codon optimized Rs-rbcLS operon, themessenger RNA (mRNA) abundance was ~25%of rbcL transcript and RsRubisco ~40% the Rubisco content in WT tobacco. To mitigate the low activation status of RsRubisco in tobRsLS (~23% sites active under ambient CO2), the metabolic repair protein RsRca (Rs-activase) was introduced via nuclear transformation. RsRca production in the tobRsLS::X progeny matched endogenous tobacco Rca levels (~1 μmol protomer.m2) and enhanced RsRubisco activation to 75% under elevated CO2(1%, vol/vol) growth. Accordingly, the rate of photosynthesis and growth in the tobRsLS::X lines were improved >twofold relative to tobRsLS. Other tobacco lines producing RsRubisco containing alternate diatom and red algae S-subunits were nonviable as CO2-fixation rates (kcatc) were reduced >95%and CO2/O2specificity impaired 30-50%. We show differences in hybrid andWT RsRubisco biogenesis in tobacco correlated with assembly in Escherichia coli advocating use of this bacterium to preevaluate the kinetic and chloroplast compatibility of engineered RsRubisco, an isoform amenable to directed evolution.

    Original languageEnglish
    Pages (from-to)25890-25896
    Number of pages7
    JournalProceedings of the National Academy of Sciences of the United States of America
    Issue number41
    Publication statusPublished - 13 Oct 2020


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