Interaction between sugar and abscisic acid signalling during early seedling development in Arabidopsis

Sugars regulate important processes and affect the expression of many genes in plants. Characterization of Arabidopsis (Arabidopsis thaliana) mutants with altered sugar sensitivity revealed the function of abscisic acid (ABA) signalling in sugar responses. However, the exact interaction between sugar signalling and ABA is obscure. Therefore ABA deficient plants with constitutive ABI4 expression (aba2-1/35S::ABI4) were generated. Enhanced ABI4 expression did not rescue the glucose insensitive (gin) phenotype of aba2 seedlings indicating that other ABA regulated factors are essential as well. Interestingly, both glucose and ABA treatment of Arabidopsis seeds trigger a post-germination seedling developmental arrest. The glucose-arrested seedlings had a drought tolerant phenotype and showed glucose-induced expression of ABSCISIC ACID INSENSITIVE3 (ABI3), ABI5 and LATE EMBRYOGENESIS ABUNDANT (LEA) genes reminiscent of ABA signalling during early seedling development. ABI3 is a key regulator of the ABA-induced arrest and it is shown here that ABI3 functions in glucose signalling as well. Multiple abi3 alleles have a glucose insensitive (gin) phenotype comparable to that of other known gin mutants. Importantly, glucose-regulated gene expression is disturbed in the abi3 background. Moreover, abi3 was insensitive to sugars during germination and showed sugar insensitive (sis) and sucrose uncoupled (sun) phenotypes. Mutant analysis further identified the ABA response pathway genes ENHANCED RESPONSE TO ABA1 (ERA1) and ABI2 as intermediates in glucose signalling. Hence, three previously unidentified sugar signalling genes have been identified, showing that ABA and glucose signalling overlap to a larger extend than originally thought

Sugar effects on early seedling development in Arabidopsis

Sugars affect a broad variety of processes,from growth and development to gene expression.Although it has already been shown that sugars act assignaling molecules, little is known about the mechanismsby which plants respond to them. Muchprogress has been made on understanding sugarsensing and signaling thanks to the analysis ofmutants with abnormal sugar response. Some of thegenetic strategies applied are based on the inhibitoryeffect of sugar on post-germinative development ofArabidopsis thaliana. High concentrations of exogenoussugars delay germination and arrest earlygrowth, preventing seedlings from expanding cotyledonsand developing true leaves and an extensive rootsystem. The characterization of several Arabidopsismutants identified for their altered sugar sensitivityhas disclosed a network in which sugars and planthormones cooperate to control seedling development.Remarkably, many mutations turned out to be novelalleles of hormone-related genes, mainly ABA andethylene

Metabolite Control of Translation by Conserved Peptide uORFs: The Ribosome as a Metabolite Multi-sensor

The regulation of gene expression is intensely investigated in diverse biological systems. Gene expression involves RNA transcription, RNA splicing, RNA stability, translation, posttranslational modification and protein stability. Particular attention has been given to mRNA levels due to advances in microarray analysis and RNA-sequencing techniques. However, transcript levels do not necessarily correlate with protein levels or functionality (Conrads et al., 2005; Gibon et al., 2006; Bianchini et al., 2008) and complex layers of posttranscriptional regulation have been uncovered, foremost mRNA translation. Translation can be regulated both globally and in a transcript-specific manner. Examples of global mRNA translational regulation include availability of ribosomes, and translation initiation, elongation and termination factors. In transcript-specific translational regulation individual mRNA species or mRNA groups are selectively translated. For example, mRNAs can be sequestered in stress granules, removing them from the translatable mRNA pool (Chantarachot and Bailey-Serres, 2017). mRNA sequence or structural features can affect translatability directly or indirectly, the latter via small RNAs or mRNA binding proteins (reviewed in Merchante et al., 2017). Upstream open reading frames (uORFs) have been shown to participate in both global and transcript-specific regulation (Von Arnim et al., 2014). Here, recent advances in translation regulation by uORFs are discussed, focusing on uORFs encoding sequence conserved peptides (CPuORFs)

The Effect of Fructan on Membrane Lipid Organization and Dynamics in the Dry State

Fructans are a group of fructose-based oligo- and polysaccharides, which appear to be involved in membrane preservation during dehydration by interacting with the membrane lipids. To get further understanding of the protective mechanism, the consequences of the fructan-membrane lipid interaction for the molecular organization and dynamics in the dry state were studied. POPC and DMPC were investigated in the dry state by (2)H, (31)P NMR, and Fourier transform infrared spectroscopy using two types of fructan and dextran. The order-disorder transition temperature of dry POPC was reduced by 70°C in the presence of fructan. Fructan increased the mobility of the acyl chains, but immobilized the lipid headgroup region. Most likely, fructans insert between the headgroups of lipids, thereby spacing the acyl chains. This results in a much lower phase transition temperature. The headgroup is immobilized by the interaction with fructan. The location of the interaction with the lipid headgroup is different for the inulin-type fructan compared to the levan-type fructan, since inulin shows interaction with the lipid phosphate group, whereas levan does not. Dextran did not influence the phase transition temperature of dry POPC showing that reduction of this temperature is not a general property of polysaccharides

Metabolite Control of Translation by Conserved Peptide uORFs: The Ribosome as a Metabolite Multi-sensor

The regulation of gene expression is intensely investigated in diverse biological systems. Gene expression involves RNA transcription, RNA splicing, RNA stability, translation, posttranslational modification and protein stability. Particular attention has been given to mRNA levels due to advances in microarray analysis and RNA-sequencing techniques. However, transcript levels do not necessarily correlate with protein levels or functionality (Conrads et al., 2005; Gibon et al., 2006; Bianchini et al., 2008) and complex layers of posttranscriptional regulation have been uncovered, foremost mRNA translation. Translation can be regulated both globally and in a transcript-specific manner. Examples of global mRNA translational regulation include availability of ribosomes, and translation initiation, elongation and termination factors. In transcript-specific translational regulation individual mRNA species or mRNA groups are selectively translated. For example, mRNAs can be sequestered in stress granules, removing them from the translatable mRNA pool (Chantarachot and Bailey-Serres, 2017). mRNA sequence or structural features can affect translatability directly or indirectly, the latter via small RNAs or mRNA binding proteins (reviewed in Merchante et al., 2017). Upstream open reading frames (uORFs) have been shown to participate in both global and transcript-specific regulation (Von Arnim et al., 2014). Here, recent advances in translation regulation by uORFs are discussed, focusing on uORFs encoding sequence conserved peptides (CPuORFs)

Proteomic LC-MS analysis of Arabidopsis cytosolic ribosomes : Identification of ribosomal protein paralogs and re-annotation of the ribosomal protein genes

UNLABELLED: Arabidopsis thaliana cytosolic ribosomes are large complexes containing eighty-one distinct ribosomal proteins (r-proteins), four ribosomal RNAs (rRNA) and a plethora of associated (non-ribosomal) proteins. In plants, r-proteins of cytosolic ribosomes are each encoded by two to seven different expressed and similar genes, forming an r-protein family. Distinctions in the r-protein coding sequences of gene family members are a source of variation between ribosomes. We performed proteomic investigation of actively translating cytosolic ribosomes purified using both immunopurification and a classic sucrose cushion centrifugation-based protocol from plants of different developmental stages. Both 1D and 2D LC-MS(E) with data-independent acquisition as well as conventional data-dependent MS/MS procedures were applied. This approach provided detailed identification of 165 r-protein paralogs with high coverage based on proteotypic peptides. The detected r-proteins were the products of the majority (68%) of the 242 cytosolic r-protein genes encoded by the genome. A total of 70 distinct r-proteins were identified. Based on these results and information from DNA microarray and ribosome footprint profiling studies a re-annotation of Arabidopsis r-proteins and genes is proposed. This compendium of the cytosolic r-protein proteome will serve as a template for future investigations on the dynamic structure and function of plant ribosomes. BIOLOGICAL SIGNIFICANCE: Translation is one of the most energy demanding processes in a living cell and is therefore carefully regulated. Translational activity is tightly linked to growth control and growth regulating mechanism. Recently established translational profiling technologies, including the profiling of mRNAs associated with polysomes and the mapping of ribosome footprints on mRNAs, have revealed that the expression of gene expression is often fine-tuned by differential translation of gene transcripts. The eukaryotic ribosome, the hub of these important processes, consists of close to eighty different proteins (depending on species) and four large RNAs assembled into two highly conserved subunits. In plants and to lesser extent in yeast, the r-proteins are encoded by more than one actively transcribed gene. As r-protein gene paralogs frequently do not encode identical proteins and are regulated by growth conditions and development, in vivo ribosomes are heterogeneous in their protein content. The regulatory and physiological importance of this heterogeneity is unknown. Here, an improved annotation of the more than two hundred r-protein genes of Arabidopsis is presented that combines proteomic and advanced mRNA expression data. This proteomic investigation and re-annotation of Arabidopsis ribosomes establish a base for future investigations of translational control in plants