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Abstract Biomolecular condensates are membraneless organelle-like structures that can concentrate molecules and often form through liquid-liquid phase separation. Biomolecular condensate assembly is tightly regulated by developmental and environmental cues. Although research on biomolecular condensates has intensified in the past 10 years, our current understanding of the molecular mechanisms and components underlying their formation remains in its infancy, especially in plants. However, recent studies have shown that the formation of biomolecular condensates may be central to plant acclimation to stress conditions. Here, we describe the mechanism, regulation, and properties of stress-related condensates in plants, focusing on stress granules and processing bodies, two of the most well-characterized biomolecular condensates. In this regard, we showcase the proteomes of stress granules and processing bodies, in an attempt to suggest methods for elucidating the composition and function of biomolecular condensates. Finally, we discuss how biomolecular condensates modulate stress responses and how they might be used as targets for biotechnological efforts to improve stress tolerance. 

Tomato (Solanum lycopersicum) fruit store carbon as starch during early development and mobilize it at the onset of ripening. Starch accumulation has been suggested to buffer fluctuations in carbon supply to the fruit under abiotic stress, and contribute to sugar levels in ripe fruit. However, the role of starch accumulation and metabolism during fruit development is still unclear. Here we show that the tomato mutant adpressa (adp) harbors a mutation in a gene encoding the small subunit of ADP-glucose pyrophosphorylase that abolishes starch synthesis. The disruption of starch biosynthesis causes major transcriptional and metabolic remodeling in adp fruit but only minor effects on fruit size and ripening. Changes in gene expression and metabolite profiles indicate that the lack of carbon flow into starch increases levels of soluble sugars during fruit growth, triggers a readjustment of central carbohydrate and lipid metabolism, and activates growth and stress protection pathways. Accordingly, adp fruits are remarkably resistant to blossom-end rot, a common physiological disorder induced by environmental stress. Our results provide insights into the effects of perturbations of carbohydrate metabolism on tomato fruit development, with potential implications for the enhancement of protective mechanisms against abiotic stress in fleshy fruit.

 

Growing knowledge about crop domestication, combined with increasingly powerful gene-editing toolkits, sets the stage for the continual domestication of crop wild relatives and other lesser-known plant species. 

Deregulating the shikimate pathway markedly increases aromatic amino acid production and carbon fixation in Arabidopsis. 

The unique flavors of different fruits depend upon complex blends of soluble sugars, organic acids, and volatile organic compounds. 2‐Phenylethanol and phenylacetaldehyde are major contributors to flavor in many foods, including tomato. In the tomato fruit, glucose, and fructose are the chemicals that most positively contribute to human flavor preferences. We identified a gene encoding a tomato aldo/keto reductase,Sl‐AKR9, that is associated with phenylacetaldehyde and 2‐phenylethanol contents in fruits. Two distinct haplotypes were identified; one encodes a chloroplast‐targeted protein while the other encodes a transit peptide‐less protein that accumulates in the cytoplasm. Sl‐AKR9 effectively catalyzes reduction of phenylacetaldehyde to 2‐phenylethanol. The enzyme can also metabolize sugar‐derived reactive carbonyls, including glyceraldehyde and methylglyoxal. CRISPR‐Cas9‐induced loss‐of‐function mutations inSl‐AKR9significantly increased phenylacetaldehyde and lowered 2‐phenylethanol content in ripe fruit. Reduced fruit weight and increased soluble solids, glucose, and fructose contents were observed in the loss‐of‐function fruits. These results reveal a previously unidentified mechanism affecting two flavor‐associated phenylalanine‐derived volatile organic compounds, sugar content, and fruit weight. Modern varieties of tomato almost universally contain the haplotype associated with larger fruit, lower sugar content, and lower phenylacetaldehyde and 2‐phenylethanol, likely leading to flavor deterioration in modern varieties.

 

Tremendous chemical diversity is the hallmark of plants and is supported by highly complex biochemical machinery. Plant metabolic enzymes originated and were transferred from eukaryotic and prokaryotic ancestors and further diversified by the unprecedented rates of gene duplication and functionalization experienced in land plants. Unlike microbes, which have frequent horizontal gene transfer events and multiple inputs of energy and organic carbon, land plants predominantly rely on organic carbon generated from CO 2 and have experienced very few, if any, gene transfers during their recent evolutionary history. As such, plant metabolic networks have evolved in a stepwise manner and on existing networks under various evolutionary constraints. This review aims to take a broader view of plant metabolic evolution and lay a framework to further explore underlying evolutionary mechanisms of the complex metabolic network. Understanding the underlying metabolic and genetic constraints is also an empirical prerequisite for rational engineering and redesigning of plant metabolic pathways. Expected final online publication date for the Annual Review of Plant Biology, Volume 72 is May 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates. 

Abiotic stresses reduce crop growth and yield in part by disrupting metabolic homeostasis and triggering responses that change the metabolome. Experiments designed to understand the mechanisms underlying these metabolomic responses have usually not used agriculturally relevant stress regimes. We therefore subjected maize plants to drought, salt, or heat stresses that mimic field conditions and analyzed leaf responses at metabolome and transcriptome levels. Shared features of stress metabolomes included synthesis of raffinose, a compatible solute implicated in tolerance to dehydration. In addition, a marked accumulation of amino acids including proline, arginine, and γ-aminobutyrate combined with depletion of key glycolysis and tricarboxylic acid cycle intermediates indicated a shift in balance of carbon and nitrogen metabolism in stressed leaves. Involvement of the γ-aminobutyrate shunt in this process is consistent with its previously proposed role as a workaround for stress-induced thiamin-deficiency. Although convergent metabolome shifts were correlated with gene expression changes in affected pathways, patterns of differential gene regulation induced by the three stresses indicated distinct signaling mechanisms highlighting the plasticity of plant metabolic responses to abiotic stress. 

The emergence of type III polyketide synthases (PKSs) was a prerequisite for the conquest of land by the green lineage.Within the PKS superfamily, chalcone synthases (CHSs) provide the entry point reaction to the flavonoid pathway, while LESS ADHESIVE POLLEN 5 and 6 (LAP5/6) provide constituents of the outer exine pollen wall. To study the deep evolutionary history of this key family, we conducted phylogenomic synteny network and phylogenetic analyses of whole-genome data from 126 species spanning the green lineage including Arabidopsis thaliana, tomato (Solanum lycopersicum),and maize (Zea mays). This study thereby combined study of genomic location and context with changes in gene sequen-ces. We found that the two major clades, CHS and LAP5/6 homologs, evolved early by a segmental duplication event priorto the divergence of Bryophytes and Tracheophytes. We propose that the macroevolution of the type III PKS superfamily isgoverned by whole-genome duplications and triplications. The combined phylogenetic and synteny analyses in this studyprovide insights into changes in the genomic location and context that are retained for a longer time scale with more re-cent functional divergence captured by gene sequence alterations. 

The chemical complexity of metabolomes goes hand in hand with their functional diversity. Small molecules have many essential roles, many of which are executed by binding and modulating the function of a protein partner. The complex and dynamic protein–metabolite interaction (PMI) network underlies most if not all biological processes, but remains under‐characterized. Herein, we highlight how co‐fractionation mass spectrometry (CF‐MS), a well‐established approach to map protein assemblies, can be used for proteome and metabolome identification of the PMIs. We will review recent CF‐MS studies, discuss the main advantages and limitations, summarize the available CF‐MS guidelines, and outline future challenges and opportunities.