Abstract
Bienertia sinuspersici is a terrestrial plant that performs C4 photosynthesis within individual cells through operating a carbon concentrating mechanism between different subcellular domains including two types of chloroplasts. It is currently unknown how differentiation of two highly specialized chloroplasts within the same cell occurs as no similar cases have been reported. Here we show that this differentiation in photosynthetic cells of B. sinuspersici is enabled by a transit peptide (TP) mediated selective protein targeting mechanism. Mutations in the TPs cause loss of selectivity but not general loss of chloroplast import, indicating the mechanism operates by specifically blocking protein accumulation in one chloroplast type. Hybrid studies indicate that this selectivity is transferable to transit peptides of plants which perform C4 by cooperative function of chloroplasts between two photosynthetic cells. Codon swap experiments as well as introducing an artificial bait mRNA show that RNA affects are not crucial for the sorting process. In summary, our analysis shows how the mechanism of subcellular targeting to form two types of chloroplast within the same cell can be achieved. This information is not only crucial for understanding single-cell C4 photosynthesis; it provides new insights in control of subcellular protein targeting in cell biology.
Highlights
A unique subcellular compartmentalization which to date has not been observed for other plants
Two structural variants of SCC4 exist: In Suaeda aralocaspica, two morphologically, biochemically and physiologically different types of chloroplast are located at opposing poles of the photosynthetic cells[9,11], whereas in the three other species, one chloroplast type (central (C) chloroplasts) is located in an internal compartment at the center of the cell and the other chloroplast type is located in the periphery close to the plasma membrane (peripheral (P) chloroplasts)[7,8,10,12]
We provide the first experimental evidence on how subcellular targeting to specialized chloroplasts works and on how SCC4 species can use this to perform C4 photosynthesis within individual cells
Summary
A unique subcellular compartmentalization which to date has not been observed for other plants. The unique subcellular compartmentalization and the specialized biochemistry of the two chloroplast types observed in SCC4 species develop gradually during ontogenesis. Numerous studies have demonstrated that the two chloroplast types accumulate different sets of nuclear encoded proteins according to their specific functions in the C4 and C3 cycle respectively[8,9,15,16,17,18]. In Kranz C4 species, it has been shown that many nuclear encoded proteins, either directly or indirectly related to their specific function in C4 photosynthesis, accumulate either in MC or BSC chloroplasts[22]. We provide the first experimental evidence on how subcellular targeting to specialized chloroplasts works and on how SCC4 species can use this to perform C4 photosynthesis within individual cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
