Biology subjects

Moehlmann, T.

Publications and source records attributed to Moehlmann, T..

4 recordsLinked to original sources

bioRxiv2026

Inosine Monophosphate Dehydrogenases are key players for functional development in Arabidopsis

In plants, nucleotide de novo synthesis is required throughout development to provide building blocks for the synthesis of DNA, RNA and nucleotide-derived cofactors. Inosine Monophosphate Dehydrogenases (IMPDH) are key enzymes in de novo guanylate synthesis. The genome of Arabidopsis thaliana encodes two IMPDHs and we identify IMPDH2 as the major isoform, being enzymatically active in the plant cytosol. Bimolecular fluorescence complementation (BIFC) analysis suggests that IMPDH1 and IMPDH2 interact with themselves and with Cytidine Triphosphate Synthetase (CTPS) isoforms, connecting purine and pyrimidine metabolism. Nucleotide quantification identifies IMPDH2 as bottleneck in guanylate biosynthesis, and plants lacking this isoform suffer from nucleotide imbalance and limitation, causing reductions in ribosomal RNAs by reducing Target of Rapamycin (TOR) activity. Impaired photosynthesis and growth were further consequences thereof. In contrast, strong overexpression of IMPDH1 supported growth and led to altered organ development in 10% of corresponding plants presumably due to altered auxin metabolism during embryo development. Significance statementThis study reveals that Inosine Monophosphate Dehydrogenase 2 (IMPDH2) is required for early Arabidopsis development and growth. Knock-out mutants exhibit reduced amounts of metabolites (e.g. XMP, GMP, GTP) accompanied by reduced expression of genes in the GO-Terms Ribosome and Photosynthesis at seedling stage. This leads to reduced chlorophyll levels, impaired photosynthesis, and reduced growth. Marked overexpression of IMPDH1 provoked abnormal organ development in 10% of cases presumably due to altered auxin metabolism.

plant biology↗

bioRxiv2021

CTP-Synthase 2 from Arabidopsis thaliana is required for complete embryo development

Pyrimidine de novo synthesis is an essential pathway in all organisms. The final and rate limiting step in the synthesis of the nucleotide CTP is catalyzed by CTP-Synthase (CTPS) and Arabidopsis harbors five isoforms. Single knockouts of each of these do not show apparent phenotypical alterations with the exception of CTPS2. T-DNA insertion lines for this isoform were unable to produce homozygous offspring. Here we show that CTPS2 exhibits a distinct expression pattern throughout embryo development and loss of function mutants were embryo lethal, as siliques from +/ctps2 plants contained nearly 25 % aborted seeds. This phenotype was rescued by complementation with CTPS2 under control of its endogenous promoter. Reporter lines revealed CTPS2 expression only in the tip of columella cells in embryos of the heart and later stages. Furthermore CTPS2 expression in roots, most pronounced in the columella cells, shoots and vasculature tissue of young seedlings was observed. Filial generations of +/ctps2 plants did not germinate properly, even under external cytidine supply. During embryo development CTPS2 expression was similar to the well known auxin reporter DR5. Indeed, the cloned promoter region we used in this study possesses a repeat of an auxin response element. Thus, we conclude that CTPS2 is essential for CTP supply in the developing embryo and a knockout of CTPS2 is embryo lethal.

plant biology↗

bioRxiv2020

UMP inhibition and sequential firing in aspartate transcarbamoylase open ways to regulate plant growth

Pyrimidine nucleotides are essential to plant development. We proved that Arabidopsis growth can be inhibited or enhanced by down- or upregulating aspartate transcarbamoylase (ATC), the first committed enzyme for de novo biosynthesis of pyrimidines in plants. To understand the unique mechanism of feedback inhibition of this enzyme by uridine 5-monophosphate (UMP), we determined the crystal structure of the Arabidopsis ATC trimer free and bound to UMP, demonstrating that the nucleotide binds and blocks the active site. The regulatory mechanism relies on a loop exclusively conserved in plants, and a single-point mutation (F161A) turns ATC insensitive to UMP. Moreover, the structures in complex with a transition-state analog or with carbamoyl phosphate proved a mechanism in plant ATCs for sequential firing of the active sites. The disclosure of the unique regulatory and catalytic properties suggests new strategies to modulate ATC activity and to control de novo pyrimidine synthesis and plant growth.

plant biology↗

bioRxiv2019

Differential degradation of RNA species by autophagy related pathways in plants

An important function of the plant vacuole is the recycling of the delivered proteins and RNA by autophagy. We provide the first plant vacuolar small RNome by isolation of intact vacuoles from Barley and Arabidopsis, subsequent RNA purification and Next Generation Sequencing. In these vacuolar sRNomes, all types of cellular RNAs were found including those of chloroplast origin, suggesting a bulk-type of RNA transfer to, and breakdown in vacuoles. ATG5 is a major representative of autophagy genes and the vacuolar RNA composition in corresponding knockout plants differed clearly from controls as most chloroplast derived RNA species were missing. Moreover, the read length distribution of RNAs found in ATG5 mutants differed to control samples, indicating altered RNA processing. In contrast, vacuolar RNA length and composition of plants lacking the vacuolar RNase2 (rns2-2), involved in cellular RNA homeostasis, showed minor alterations, only. Our data therefore suggests that mainly autophagy components are responsible for selective transport and targeting of different RNA species into the vacuole for degradation. In addition, mature miRNAs were detected in all vacuolar preparations, however in ATG5 mutants at much lower frequency, indicating a new biological role for vacuolar miRNAs apart from becoming degraded.

plant biology↗