Project description:Leaf senescence, the last step of leaf development, is a highly regulated process, modulated by a number of internal and external factors. During the senescence process resources like nitrogen (N) are remobilized from senescent tissues to sink tissues. This intrinsically depends on the accurate dispersion of resources according to sink strength of various organs competing with each other. Consequently, N deficiency accelerates barley leaf senescence and its resupply can delay the senescence progression. In order to identify genetic and metabolic factors that regulate leaf senescence in response to N supply, transcriptomic and global metabolic rearrangements were analyzed in barley primary at early and later stages of N deprivation, and after N resupply to N-deficient plants.
Project description:Responses to altered source–sink balance have been characterized in many crops at the physiological level, but the underlying genetic and molecular mechanisms are largely unknown. Detailed transcriptional profiling was performed in partially defoliated and shaded tomato plants to explore the effect of reduced source-to-sink ratio on molecular changes in the remaining source leaves. Transcription profiles of the remaining leaves 48 h after partial defoliation or partial shading were compared to leaves of control plants. Common significantly altered genes in the two treatments were assumed to be related to the reduced source-to-sink ratio. Sets of major genes in the abscisic acid, ethylene and gibberellin signal-transduction pathways were downregulated by both treatments. On the other hand, genes encoding cytokinin biosynthesis were upregulated. Most genes coding for transcription factors were also downregulated, especially those related to biotic and abiotic stress responses. Perhaps the most pronounced effect of reduced source-to-sink ratio was related to genes involved in the regulation of photosynthetic activity. Numerous genes coding for light-harvesting proteins, as well as those encoding plastocyanin, ferredoxin and ferredoxin NADP+ oxidoreductase were upregulated. Direct spectrophotometric analyses showed higher maximal potential activity of photosystem I with reduced source-to-sink ratio. As expected, the increased capacity for photosynthetic activity was associated with upregulation of almost all genes coding for the Calvin–Benson cycle and those encoding ATP biosynthesis in the mitochondria. Numerous transcriptional changes were observed 48 h after reducing source-to-sink ratio. Major genes in the photosynthetic-activity pathways were upregulated, whereas those in the pathways of defense mechanisms and responses to stress were downregulated. Genes involved in leaf senescence were also downregulated, suggesting that in addition to increased photosynthetic activity, the remaining leaves undergo a process of rejuvenation.
Project description:During the senescence stage, leaves undergo degeneration and relocate nutrients accumulated during the growth stage to sink parts such as seeds, critically contributing to plants’ productivity and fitness. Here, we asked how leaf transcriptome is regulated during the senescence stage by performing directional sequencing of total and small RNAs for the entire lifespan of Arabidopsis leaves.
Project description:Source-to-sink carbon (C) allocation driven by the sink strength, i.e., the ability of a sink organ to import C, plays a central role in tissue growth and biomass productivity. However, molecular drivers of sink strength have not been thoroughly characterized in trees. Auxin, as a major plant phytohormone, regulates the mobilization of photoassimilates in source tissues and elevates the translocation of carbohydrates toward sink organs, including roots. In this study, we used an ‘auxin-stimulated carbon sink’ approach to understand the molecular processes involved in the long-distance source-sink C allocation in poplar. Poplar cuttings were foliar sprayed with polar auxin transport modulators, including auxin enhancers (AE) (i.e., IBA and IAA) and auxin inhibitor (AI) (i.e., NPA), followed by a comprehensive analysis of leaf, stem, and root tissues using biomass evaluation, phenotyping, C isotope labeling, metabolomics, and transcriptomics approaches. Auxin modulators altered root dry weight and branching pattern, and AE increased photosynthetically fixed C allocation from leaf to root tissues. The transcriptome analysis identified highly expressed genes in root tissue under AE condition including transcripts encoding polygalacturonase and β-amylase that could increase the sink size and activity. Metabolic analyses showed a shift in overall metabolism including an altered relative abundance levels of galactinol, and an opposite trend in citrate levels in root tissue under AE and AI conditions. In conclusion, we postulate a model suggesting that the source-sink C relationships in poplar could be fueled by mobile sugar alcohols, starch metabolism-derived sugars, and TCA-cycle intermediates as key molecular drivers of sink strength.
Project description:To examine the role of formation of a strong sink during leaf senescence, we compared the expression profile of the flag leaf of three different sterile mutant lines with fertile plants. The fertile and sterile lines showed basically similar expression profiles of flag leaves sampled at the same time. However, the fertile lines showed more rapid and enhanced change in transcriptome as compared to the sterile lines indicating that leaf senescence initiated independent of sink formation and is accelerated by sink formation.
Project description:To decipher gene expression controlled by the five highly homologous group S1 bZIP transcription factors during the reproductive growth phase of Arabidopsis thaliana, we generated triple (bzip2/-11/-44) and quintuple (bzip1/-2/-11/-44/-53) mutants of these factors using CRISPR/Cas9 and analysed gene expression in distinct C source (source leaves) or C sink (sink leaves, rosette buds, flowers) tissues.
Project description:During the senescence stage, leaves undergo degeneration and relocate nutrients accumulated during the growth stage to sink parts such as seeds, critically contributing to plantsâ productivity and fitness. Here, we asked how leaf transcriptome is regulated during the senescence stage by performing directional sequencing of total and small RNAs for the entire lifespan of Arabidopsis leaves. The total RNA and small RNA profiles of the Arabidopsis leaf along lifespan (14 and 7 time points, respectively) were generated by next-generation sequencing using Illumina Hiseq2000. Two independent biological replicates were used for each experiment.
Project description:To examine the role of formation of a strong sink during leaf senescence, we compared the expression profile of the flag leaf of three different sterile mutant lines with fertile plants. The fertile and sterile lines showed basically similar expression profiles of flag leaves sampled at the same time. However, the fertile lines showed more rapid and enhanced change in transcriptome as compared to the sterile lines indicating that leaf senescence initiated independent of sink formation and is accelerated by sink formation. Three independent mutant lines, namely, pair1, pair2, and mel1-1, and fertile plants (homozygous or heterozygous) derived from each segregating population were used for comparison. The flag leaves were sampled at initiation of heading, 1 week after heading (WAH), 2 WAH, and 3 WAH, with three biological replicates.
Project description:Soybean plants that do not produce a sink, such as depodded or male sterile plants, exhibit physiological and morphological changes during the reproductive stages, including increased levels of nitrogen and starch in the leaves and a delayed senescence. To identify transcriptional changes that occur in leaves of sink-limited plants, we used RNAseq to compare gene expression levels in trifoliate leaves from depodded and ms6 male sterile plants and control plants. In sink-limited tissues, we observed a deferral of the expression of senescence-associated genes and a continued high expression of genes associated with the maturity phase of leaf development. We identified GO-terms associated with growth and development and storage protein in sink limited tissues. We also identified that the bHLH. ARFs, and SBP transcription factors were expressed in sink limited tissues while the senescing control leaves expressed WRKY and NAC transcription factors. We identified genes that were not expressed during normal leaf development but highly expressed in sink-limited plants, including the D4 “non-yellowing” gene. These changes highlighted several metabolic pathways that were involved in distinct modes of resource parttioning in the “stay green” leaves.