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bioRxiv · 10.64898/2026.01.26.701875

Translesion DNA synthesis on pyrimidine dimers by Plant organellar DNA polymerases is metal-dependent

Baruch-Torres, N.·Park, J.·Castro-Torres, E.·Iwai, S.·Yin, Y. W.·Brieba, L. G.
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Abstract

Ultraviolet (UV) radiation generates crosslinked DNA lesions--primarily cyclobutane pyrimidine dimers (CPDs) and [6-4] photoproducts ([6-4] PPs)--that block the progression of replicative DNA polymerases. In plants, these lesions are efficiently removed from nuclear DNA by dedicated repair pathways; however, comparable repair mechanisms are absent in plastids and mitochondria. Consequently, how plant organellar DNA polymerases (POPs) tolerate or bypass UV-induced damage has remained unclear. Here, we show that the two Arabidopsis thaliana organellar polymerases, AtPolIs, possess robust translesion synthesis (TLS) activity across CPDs. Although wild-type enzymes display only limited extension across [6-4] PPs, removal of their exonuclease function dramatically enhances bypass, yielding an efficiency of replication across the [6-4] PP that closely resembles that observed on an undamaged template. This establishes AtPolI as the first known replicative DNA polymerase capable of efficiently bypassing a [6-4] PP. We further demonstrate that TLS across UV photoproducts relies on three unique amino acid insertions within the AtPolI polymerase domain, as deletion of any single insertion abolishes TLS. Notably, Mn{superscript 2} can restore TLS activity in these variants, but only for CPD lesions. Together, these findings identify AtPolIs as the first plant organellar replicases with intrinsic [6-4] PP bypass capability and define the structural features that enable this function. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=97 SRC="FIGDIR/small/701875v1_ufig1.gif" ALT="Figure 1"> View larger version (15K): org.highwire.dtl.DTLVardef@f497bcorg.highwire.dtl.DTLVardef@15ba2eorg.highwire.dtl.DTLVardef@724e29org.highwire.dtl.DTLVardef@697c8b_HPS_FORMAT_FIGEXP M_FIG C_FIG

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Baruch-Torres, N., Park, J., Castro-Torres, E., Iwai, S., Yin, Y. W., Brieba, L. G.. 2026-01-27. Translesion DNA synthesis on pyrimidine dimers by Plant organellar DNA polymerases is metal-dependent. https://doi.org/10.64898/2026.01.26.701875

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