An inosine triphosphate pyrophosphatase safeguards plant nucleic acids from aberrant purine nucleotides

Abstract

Inosine is deaminated adenosine. Inosine is enzymatically introduced in some plant tRNAs but not in other RNAs or DNA. Nonetheless, our data show that RNA and DNA from Arabidopsis thaliana contain (deoxy)inosine, probably derived from non-enzymatic adenosine deamination in nucleic acids and usage of (deoxy)inosine triphosphate (ITP / dITP) during nucleic acid synthesis. We identified a plant INOSINE TRIPHOSPHATE PYROPHOSPHATASE (ITPA) which is conserved in many organisms. Arabidopsis ITPA dephosphorylates deaminated nucleoside di- and triphosphates to their respective monophosphates. ITPA mutation causes inosine di- and triphosphate accumulation in vivo and an elevated (deoxy)inosine content in DNA and RNA. Cadmium-induced oxidative stress, known to foster deamination, leads to more ITP in the wildtype and especially in itpa mutants suggesting that ITP originates from ATP deamination. By contrast, erroneous IMP phosphorylation by AMP kinases seems not to be a major ITP source in vivo although these enzymes phosphorylate IMP in vitro. Mutation of ITPA causes salicylic acid (SA) accumulation, early senescence and upregulation of transcripts associated with immunity and senescence. ITPA is part of a molecular protection system, preventing accumulation of (d)ITP, its usage for nucleic acid synthesis, and probably nucleic acid stress leading to SA accumulation, stress gene induction and early senescence.

Changes in Medicago truncatula seed proteome along the rehydration–dehydration cycle highlight new players in the genotoxic stress response

“…These findings were further corroborated by Yoneshima et al (2016) who investigated the effects of exogenous dI added to the culture medium of ITPAdefective human cell lines. Straube et al (2022) recently investigated the Arabidopsis ipta mutants, showing that the enzyme contributes to safeguarding nucleic acids from the incorporation of aberrant purine nucleotides. The evolutionarily conserved RNA helicase MAC7 is the homolog of the human MAC7 or Aquarius helicase.…”

“…In this study, a label-free LC-MS/MS proteomics approach was used to characterize the Medicago truncatula seed proteome along the rehydration/dehydration cycle of a standard vigorization treatment [hydropriming (HP) plus dry-back] and during postpriming imbibition to tackle changes correlated to improved germination performance and identify novel players involved in the genotoxic stress response in seeds. Considering the impact of genotoxic stress on the seed response to priming and the related open questions (Pagano et al 2022a;2022b;Pagano et al, 2023), attention was focused on those proteins with potential or documented roles in genome maintenance, such as MtITPA (INOSINE TRIPHOSPHATE PYROPHOSPHORYLASE) (Yoneshima et al, 2016;Straube et al, 2022). MtITPA was further investigated in the context of seed priming, and its contribution to the enhanced genotoxic stress response of the M. truncatula primed seeds is discussed.…”