The dependency of red Rubisco on its cognate activase for enhancing plant photosynthesis and growth
Date
2020
Authors
Gunn, Laura
Martin Avila, Elena
Birch, Rosemary
Whitney, Spencer
Journal Title
Journal ISSN
Volume Title
Publisher
National Academy of Sciences (USA)
Abstract
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 (kcat
c) were reduced >95%and
CO2/O2 specificity 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.
Description
Keywords
chloroplast transformation, Rubisco activase, carbon fixation, photosynthesis
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PNAS - Proceedings of the National Academy of Sciences of the United States of America
Type
Journal article
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Restricted until
2099-12-31
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