The ribokinases of Arabidopsis thaliana and Saccharomyces cerevisiae are required for ribose recycling from nucleotide catabolism, which in plants is not essential to survive prolonged dark stress

Abstract

SummaryNucleotide catabolism in Arabidopsis thaliana and Saccharomyces cerevisiae leads to the release of ribose, which requires phosphorylation to ribose-5-phosphate mediated by ribokinase (RBSK). We aimed to characterize RBSK in plants and yeast, to quantify the contribution of plant nucleotide catabolism to the ribose pool, and to investigate whether ribose carbon contributes to dark stress survival of plants.We performed a phylogenetic analysis and determined the kinetic constants of plantexpressed Arabidopsis and yeast RBSKs. Using mass spectrometry, several metabolites were quantified in AtRBSK mutants and double mutants with genes of nucleoside catabolism. Additionally, the dark stress performance of several nucleotide metabolism mutants and rbsk was compared.The plant PfkB family of sugar kinases forms nine major clades likely representing distinct biochemical functions, one of them RBSK. Nucleotide catabolism is the dominant ribose source in plant metabolism and is highly induced by dark stress. However, rbsk cannot be discerned from the wild type in dark stress. Interestingly, the accumulation of guanosine in a guanosine deaminase mutant strongly enhances dark stress symptoms.Although nucleotide catabolism contributes to carbon mobilization upon darkness and is the dominant source of ribose, the contribution appears to be of minor importance for dark stress survival.

Nucleotide Metabolism in Plants

“…5, no. 21) mutants are phenotypically normal except for a slight delay in germination (Liu et al, 2007;Schroeder et al, 2018). Mutation of HGPRT leads to guanine but not hypoxanthine accumulation in vivo, probably reflecting the fact that guanine can only be salvaged, whereas hypoxanthine can also be degraded (Baccolini and Witte, 2019).…”

“…However, NSH1 is required to activate NSH2, which is the stronger xanthosine and inosine hydrolase in the complex. Nucleoside catabolism is the major metabolic source of ribose, which is recycled to ribose 5-phosphate by ribokinase in the plastids (Riggs et al, 2016;Schroeder et al, 2018). Xanthine and hypoxanthine are catabolized by the same enzyme, xanthine dehydrogenase (XDH; Fig.…”

“…5B, #30) to (S)-allantoin Pessoa et al, 2010). Mutation of UOX leads to strong accumulation of uric acid, which is deleterious for peroxisome maintenance in the embryo, leading to a severe suppression of germination and seedling establishment (Hauck et al, 2014)-surprisingly, accumulation of similar amounts of xanthine in Arabidopsis plants lacking XDH does not lead to strong phenotypic alterations under standard growth conditions (Hauck et al, 2014;Schroeder et al, 2018;Soltabayeva et al, 2018). Allantoin must be transported from the peroxisomes to the ER for further degradation, but it is unclear how this is achieved.…”

Pre-mature senescence in the oldest leaves of low nitrate-grown Atxdh1 mutant uncovers a role for purine catabolism in plant nitrogen metabolism

“…Moreover, 234 the level of xanthine accumulated in the old leaves of Atxdh1 mutant ( Fig. 4A) was far lower than the 235 level shown recently in Atxdh1 leaves after 5 successive days in dark [calculated as ~1 µmol g -1 FW from 236 Figure 8A in (Schroeder et al, 2017)], where no significant senescence symptoms is claimed to be more 237 in the mutant compared to WT leaves (See Figure 7 in Schroeder et al, 2017). Significantly, only low 238 xanthine levels were evident in the old leaves of Ataln and Ataah mutants and WT plants ( Fig.…”

The TIR-domain containing effectors BtpA and BtpB fromBrucella abortusblock energy metabolism

“…Although most of these genes have not been yet assigned a bona fide function in yeast, a subset of them, INM2, RBK1 , and DOG2 are sugar or inositol phosphorylating/dephosphorylating enzymes related to metabolic pathways (S3 Table). DOG2 encodes a 2-deoxyglucose-6 phosphate phosphatase and its overexpression overcomes toxicity of this glycolytic inhibitor [26], and RBK1 encodes a putative ribokinase, which has been recently shown to be catalytically active [27]. These results suggest that metabolic shifts related to carbon source usage counteract BtpB toxicity.…”