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

Abstract

In plants, inosine is enzymatically introduced in some 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 nonenzymatic adenosine deamination in nucleic acids and usage of (deoxy)inosine triphosphate (dITP and ITP) during nucleic acid synthesis.We combined biochemical approaches, LC-MS, as well as RNA-Seq to characterize a plant INOSINE TRIPHOSPHATE PYROPHOSPHATASE (ITPA) from A. thaliana, which is conserved in many organisms, and investigated the sources of deaminated purine nucleotides in plants.Inosine triphosphate pyrophosphatase dephosphorylates deaminated nucleoside di-and triphosphates to the respective monophosphates. ITPA loss-of-function causes inosine di-and triphosphate accumulation in vivo and an elevated inosine and deoxyinosine content in RNA and DNA, respectively, as well as salicylic acid (SA) accumulation, early senescence, and upregulation of transcripts associated with immunity and senescence. Cadmium-induced oxidative stress and biochemical inhibition of the INOSINE MONOPHOSPHATE DEHYDRO-GENASE leads to more IDP and ITP in the wild-type (WT), and this effect is enhanced in itpa mutants, suggesting that ITP originates from ATP deamination and IMP phosphorylation.Inosine triphosphate pyrophosphatase is part of a molecular protection system in plants, preventing the accumulation of (d)ITP and its usage for nucleic acid synthesis.

Inosine triphosphate pyrophosphatase: A guardian of the cellular nucleotide pool and potential mediator of RNA function

“…The change reduces splicing‐efficiency and thereby reduces protein expression (Arenas et al, 2007). Notably, compound heterozygotes for the p.Pro32Thr and c.124+21A>C polymorphisms have lower erythrocyte ITPase activity than either p.Pro32Thr heterozygotes or c.124+21A>C homozygotes, consistent with the likely increased degradation rate of p.Pro32Thr‐containing dimers (Shipkova et al, 2006; Simone, Struble, et al, 2013; Straube et al, 2023; Sumi et al, 2002).…”

“…The A. thaliana ITPase, At4g13720, has very recently been characterized (Straube et al, 2023). Like ITPases from bacteria, fungi and animals, it has activity on (d)ITP and XTP, but in difference to these orthologous proteins it also has activity on IDP.…”

“…Moreover, the p.Pro32Thr change is associated with a 45% reduction in catalytic activity (Herting et al, 2010). However, it is the reduced stability of the expressed protein that is probably most relevant for the phenotype (Simone, Struble, et al, 2013; Stepchenkova et al, 2009; Straube et al, 2023). First, because accelerated degradation of ITPase‐dimers containing one or more p.Pro32Thr subunits can explain the reduction in ITPase activity in heterozygotes to below half that of wild‐types (Simone, Pavlov, & Borgstahl, 2013; Straube et al, 2023).…”

“…However, it is the reduced stability of the expressed protein that is probably most relevant for the phenotype (Simone, Struble, et al, 2013; Stepchenkova et al, 2009; Straube et al, 2023). First, because accelerated degradation of ITPase‐dimers containing one or more p.Pro32Thr subunits can explain the reduction in ITPase activity in heterozygotes to below half that of wild‐types (Simone, Pavlov, & Borgstahl, 2013; Straube et al, 2023). Next, because it explains why effects on ITPase activity and ITP accumulation are most pronounced in erythrocytes, which lack the apparatus for protein expression.…”

A mixed infection of ITPase-encoding potyvirid and secovirid in Mercurialis perennis: evidences for a convergent euphorbia-specific viral counterstrike

“…ITPases catalyze the hydrolysis of non-canonical nucleosides triphosphate (NTPs), mainly inosine and xanthosine triphosphate (ITP and XTP, respectively), which are produced by deamination of purines, for instance after oxidative stress. In cellular organisms, these enzymes are therefore essential for preventing the incorporation of ITP and XTP into DNA and RNA, thereby avoiding their deleterious mutagenic effects (Lin et al, 2001;Menezes et al, 2012;Schroader et al, 2022;Straube et al, 2022). When it comes to phytoviruses, ITPases were rst detected in two ipomoviruses, namely cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV).…”