Poster abstracts
Poster number 184 submitted by Samuel MacKinnon
Investigation of the DNA-membrane association between the chloroplast nucleoid and thylakoid membrane in Arabidopsis thaliana
Samuel MacKinnon (MCDB, Unviersity of Michigan), Ji-Hee Min (MCDB, Unviersity of Michigan), Yoonjin Cho (MCDB, Unviersity of Michigan), Miguel Palomar (MCDB, Unviersity of Michigan), Andrzej Wierzbicki (MCDB, Unviersity of Michigan)
Abstract:
The inefficiency of land plants in their uptake and assimilation of carbon dioxide from the atmosphere is a problem which is relevant for crop engineering in the wake of increased food demand as the world population grows towards a predicted ten billion human beings by 2050, and has remained intractable despite prolonged effort and significant investment. Towards that end, a more robust understanding of the physiology and regulation of the chloroplast - the organelle in which photosynthesis and carbon fixation occur - is necessary if these hurdles are ever to be overcome.
Though the chloroplast has surrendered many of its genes by transference to the central control of the nucleus over the millennia since it first joined the eukaryotic cell by endosymbiosis, it retains its own genome, copies of which are packaged with RNA and proteins into complex, heterogeneous structures known as nucleoids. In order to obtain the holistic picture of chloroplast physiology needed for future engineering efforts, detailed investigation into how the expression of encoded gene products on the chloroplast nucleoid are regulated is necessary.
Towards that end, we undertook investigation of the previously observed but unexplained association of highly transcribed regions of the chloroplast nucleoid with the thylakoid membrane, testing two hypotheses: first that a putative anchor protein could bind DNA and anchor it to the membrane, and second that co-translational transertion of highly transcribed transmembrane protein products could explain the association. Disruption of cpSRP54-dependent cotranslational thylakoid targeting did not reduce RNA polymerase occupancy at membrane-associated genes, as predicted by a transertion-dependent model. Efforts to identify putative anchor proteins have also produced negative results, underscoring the complexity of the chloroplasts organization.
References:
1. V.M. Palomar, Y. Cho, S. Fujii, M.H. Rothi, S. Jaksich, J. Min, A.N. Schlachter, J. Wang, Z. Liu, & A.T. Wierzbicki, Membrane association of active genes organizes the chloroplast nucleoid structure, Proc. Natl. Acad. Sci. U.S.A. 121 (28) e2309244121, https://doi.org/10.1073/pnas.2309244121 (2024).
Keywords: chloroplast nucleoid, plastid gene expression, transertion