UMP Kinase Regulates Chloroplast Development and Cold Response in Rice

Abstract

Pyrimidine nucleotides are important metabolites that are building blocks of nucleic acids, which participate in various aspects of plant development. Only a few genes involved in pyrimidine metabolism have been identified in rice and the majority of their functions remain unclear. In this study, we used a map-based cloning strategy to isolate a UMPK gene in rice, encoding the UMP kinase that phosphorylates UMP to form UDP, from a recessive mutant with pale-green leaves. In the mutant, UDP content always decreased, while UTP content fluctuated with the development of leaves. Mutation of UMPK reduced chlorophyll contents and decreased photosynthetic capacity. In the mutant, transcription of plastid-encoded RNA polymerase-dependent genes, including psaA, psbB, psbC and petB, was significantly reduced, whereas transcription of nuclear-encoded RNA polymerase-dependent genes, including rpoA, rpoB, rpoC1, and rpl23, was elevated. The expression of UMPK was significantly induced by various stresses, including cold, heat, and drought. Increased sensitivity to cold stress was observed in the mutant, based on the survival rate and malondialdehyde content. High accumulation of hydrogen peroxide was found in the mutant, which was enhanced by cold treatment. Our results indicate that the UMP kinase gene plays important roles in regulating chloroplast development and stress response in rice.

Nucleotide Metabolism in Plants

“…The orthologous enzyme in rice is localized in chloroplasts and participates in RNA metabolism, and the corresponding loss-of-function mutants are pale green (Zhu et al, 2016;Chen et al, 2018a). Additionally, they contain less UDP and more UMP (Dong et al, 2019), suggesting that UMP phosphorylation in the chloroplast is functionally important. The phosphorylation of thymidine 59-monophosphate (TMP) is not catalyzed by UMKs but by a dedicated TMP kinase (TMK; Fig.…”

β-N-Methylamino-L-Alanine (BMAA) Causes Severe Stress in Nostoc sp. PCC 7120 Cells under Diazotrophic Conditions: A Proteomic Study

“…Such upregulation of subunits of DNA-directed RNA polymerase may be explained by severe stress triggered by BMAA in nitrogen limitation conditions. It was demonstrated that the expression level of plant genes encoding rpoB and rpoC1 is induced by various stresses [ 66 ].…”

Metabolic and Physiological Regulation of Aspartic Acid-Mediated Enhancement of Heat Stress Tolerance in Perennial Ryegrass

“…The content of uracil has been shown to significantly decrease in soybean (Glycine max) subjected to heat or drought stress [26]. Mutants of UMP kinase became more sensitive to cold stress in rice (O. sativa), as manifested by a reduction in Chl content and photosynthesis [27]. Thymine and guanosine are important components of DNA, and it has been exhibited that thymine has a positive effect on drought tolerance of wheat (Triticum aestivum), as drought-tolerant cultivars had a higher level of thymine than that of drought-sensitive cultivars [28,29].…”