Polyprenols are synthesized by a plastidial cis - prenyltransferase 3 and influence photosynthetic performance 4 5 Tariq

RESEARCH ARTICLE 1 2 Polyprenols are synthesized by a plastidial cis-prenyltransferase 3 and influence photosynthetic performance 4 5 Tariq A. Akhtar, Przemysław Surowiecki, Hanna Siekierska, Magdalena Kania, 6 Kristen Van Gelder, Kevin A. Rea, Lilia K. A. Virta, Maritza Vatta, Katarzyna 7 Gawarecka, Jacek Wojcik, Witold Danikiewicz, Daniel Buszewicz, Ewa 8 Swiezewska, Liliana Surmacz 9 10 Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, N1G 11 2W1, Canada, 12 Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 13 02-106 Warsaw, Poland. 14 Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01224 15 Warsaw, Poland. 16 1 Corresponding authors: [email protected], [email protected]). 17 18 The authors responsible for distribution of materials integral to the findings presented in 19 this article in accordance with the policy described in the Instructions for Authors 20 (www.plantcell.org) are: Tariq A. Akhtar ([email protected]) or Liliana Surmacz 21 ([email protected]). 22 23 Short title: A central role for polyprenols in photosynthesis 24 25 One-sentence summary: A plastidial cis-prenyltransferase synthesizes a family of 26 polyprenols that accumulate in thylakoid membranes and play a central role in the 27 efficiency of photosynthetic performance. 28 29 ABSTRACT 30 Plants accumulate a family of hydrophobic polymers known as polyprenols, yet how they 31 are synthesized, where they reside in the cell, and what role they serve is largely 32 unknown. Using Arabidopsis thaliana as a model, we present evidence for the 33 involvement of a plastidial cis-prenyltransferase (AtCPT7) in polyprenol synthesis. Gene 34 inactivation and RNAi-mediated knockdown of AtCPT7 eliminated leaf polyprenols while 35 its overexpression increased their content. Complementation tests in the polyprenol36 deficient yeast ∆rer2 mutant and enzyme assays with recombinant AtCPT7 confirmed 37 that the enzyme synthesizes polyprenols of approximately 55 carbons in length using 38 geranylgeranyl diphosphate (GGPP) and isopentenyl diphosphate (IPP) as substrates. 39 Immunodetection and in vivo localization of AtCPT7 fluorescent protein fusions showed 40 that AtCPT7 resides in the stroma of mesophyll chloroplasts. The enzymatic products of 41 AtCPT7 accumulate in thylakoid membranes and in their absence, thylakoids adopt an 42 increasingly ‘fluid membrane’ state. Chlorophyll fluorescence measurements from the 43 leaves of polyprenol-deficient plants revealed impaired photosystem II operating 44 efficiency, and their thylakoids exhibited a decreased rate of electron transport. These 45 results establish that (i) plastidial AtCPT7 extends the length of GGPP to ~55 carbons, 46 which then accumulate in thylakoid membranes; and (ii) these polyprenols influence 47 photosynthetic performance through their modulation of thylakoid membrane dynamics. 48 49 Plant Cell Advance Publication. Published on June 27, 2017, doi:10.1105/tpc.16.00796