Rubisco production in maize mesophyll cells through ectopic expression of subunits and chaperones

Amber M Hotto, Coralie Salesse-Smith, Myat Lin, Florian A Busch, Isabelle Simpson, David B Stern

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Abstract C4 plants, such as maize, strictly compartmentalize Rubisco to bundle sheath chloroplasts. The molecular basis for the restriction of Rubisco from the more abundant mesophyll chloroplasts is not fully understood. Mesophyll chloroplasts transcribe the Rubisco large subunit gene and, when normally quiescent transcription of the nuclear Rubisco small subunit gene family is overcome by ectopic expression, mesophyll chloroplasts still do not accumulate measurable Rubisco. Here we show that a combination of five ubiquitin promoter-driven nuclear transgenes expressed in maize leads to mesophyll accumulation of assembled Rubisco. These encode the Rubisco large and small subunits, Rubisco assembly factors 1 and 2, and the assembly factor Bundle sheath defective 2. In these plants, Rubisco large subunit accumulates in mesophyll cells, and appears to be assembled into a holoenzyme capable of binding the substrate analog CABP (carboxyarabinitol bisphosphate). Isotope discrimination assays suggest, however, that mesophyll Rubisco is not participating in carbon assimilation in these plants, most probably due to a lack of the substrate ribulose 1,5-bisphosphate and/or Rubisco activase. Overall, this work defines a minimal set of Rubisco assembly factors in planta and may help lead to methods of regulating the C4 pathway.
Original languageEnglish
Article number4930–4937
Pages (from-to)4930-4937
Number of pages8
JournalJournal of Experimental Botany
Issue number13
Early online date30 Apr 2021
Publication statusPublished - 22 Jun 2021

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© 2021 The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email:


  • C4 photosynthesis
  • cell type specificity
  • maize
  • Rubisco
  • Rubisco assembly


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