期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2020
卷号：117
期号：41
页码：25890-25896
DOI：10.1073/pnas.2011641117
出版社：The National Academy of Sciences of the United States of America
摘要：Plant photosynthesis and growth are often limited by the activity of the CO 2 -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 ( Rs Rubisco)— a red-type Rubisco able to assemble in plant chloroplasts. In transplastomic tob Rs LS lines expressing a codon optimized Rs - rbcLS operon, the messenger RNA (mRNA) abundance was ∼25% of rbcL transcript and Rs Rubisco ∼40% the Rubisco content in WT tobacco. To mitigate the low activation status of Rs Rubisco in tob Rs LS (∼23% sites active under ambient CO 2 ), the metabolic repair protein Rs Rca ( Rs -activase) was introduced via nuclear transformation. Rs Rca production in the tob Rs LS::X progeny matched endogenous tobacco Rca levels (∼1 µmol protomer·m 2 ) and enhanced Rs Rubisco activation to 75% under elevated CO 2 (1%, vol/vol) growth. Accordingly, the rate of photosynthesis and growth in the tob Rs LS::X lines were improved >twofold relative to tob Rs LS. Other tobacco lines producing Rs Rubisco containing alternate diatom and red algae S-subunits were nonviable as CO 2 -fixation rates ( k cat c ) were reduced >95% and CO 2 /O 2 specificity impaired 30–50%. We show differences in hybrid and WT Rs Rubisco biogenesis in tobacco correlated with assembly in Escherichia coli advocating use of this bacterium to preevaluate the kinetic and chloroplast compatibility of engineered Rs Rubisco, an isoform amenable to directed evolution.
