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Plant glandular secreting trichomes are epidermal protuberances that produce structurally diverse specialized metabolites, including medically important compounds. Trichomes of many plants in the nightshade family (Solanaceae) produce O-acylsugars, and in cultivated and wild tomatoes these are mixtures of aliphatic esters of sucrose and glucose of varying structures and quantities documented to contribute to insect defense. We characterized the first two enzymes of acylsucrose biosynthesis in the cultivated tomato Solanum lycopersicum. These are type I/IV trichome-expressed BAHD acyltransferases encoded by Solyc12g006330─or S. lycopersicum acylsucrose acyltransferase 1 (Sl-ASAT1)─and Solyc04g012020 (Sl-ASAT2). These enzymes were used-in concert with two previously identified BAHD acyltransferases-to reconstruct the entire cultivated tomato acylsucrose biosynthetic pathway in vitro using sucrose and acyl-CoA substrates.Comparative genomics and biochemical analysis of ASAT enzymes were combined with in vitro mutagenesis to identify amino acids that influence CoA ester substrate specificity and contribute to differences in types of acylsucroses that accumulate in cultivated and wild tomato species. This work demonstrates the feasibility of the metabolic engineering of these insecticidal metabolites in plants and microbes.Solanum | glandular trichomes | acylsugar | specialized metabolism | genotype to phenotype P lants are masters of metabolism, producing hundreds of thousands of small molecules known as specialized metabolites, which vary widely in structure, abundance, and physical and biological properties. These metabolites tend to be produced by enzymes that evolve faster than those that produce "central" metabolites such as amino acids, nucleotides, sugars, and cofactors (1-3), and the pathways and metabolic intermediates involved in biosynthesis of many specialized metabolites remain mysterious. Despite the growing availability of genomic DNA sequences, understanding the genetic and biochemical mechanisms that contribute to this phenotypic diversity and plasticity presents enduring and major challenges in plant biochemistry. It is of great interest to understand and manipulate the biosynthesis of these biologically active molecules.Specialized metabolites typically are produced in a cell-or tissue-specific manner and are generally limited in their taxonomic distribution. Glandular secreting trichomes provide an example of such a differentiated structure; these epidermal "hairs" produce a variety of metabolites of importance to humans, including aromatic flavor components (e.g., in hops for beer and Mediterranean herbs for cooking), psychoactive cannabinoids in Cannabis, and the antimalarial drug artemisinin in Artemisia annua (4, 5).Some trichome-produced metabolites have documented direct and indirect antiherbivore activities (4, 6-8). For example, acylsugars are a group of structurally related specialized metabolites produced in plants of the nightshade family-the Solanaceae (9, 10). Characterized examples ...

Soil salinity is a major abiotic stress that limits agriculture productivity worldwide. Salicornia europaea is a succulent annual euhalophyte and one of the most salt tolerant plant species. The elucidation of its salt tolerance mechanism is of significance for generating salt-tolerant crops. In this study, we provided high resolution of proteome reference maps of S. europaea shoot and obtained evidence on the salt tolerance mechanism by analyzing the proteomic responses of this plant to high salinity. Our results demonstrated significant variations existed in 196 out of 1880 protein spots detected on CBB stained 2-DE gels. Of these, 111 proteins were identified by mass spectrometry. Among them, the majority was energy production and conversion related proteins, followed by photosynthesis and carbohydrate metabolism associated enzymes. Analysis of protein expression patters revealed that energy production and ion homeostasis associated proteins played important roles for this plant salt tolerance ability. Hierarchical clustering results revealed many proteins were involved in S. europaea salt tolerance mechanism as a dynamic network. Finally, based on our proteomic results, we brought forward a possible schematic representation of mechanism associated with the systematic salt tolerance phenotype in S. europaea.

Plants produce a myriad of taxonomically restricted specialized metabolites. This diversity—and our ability to correlate genotype with phenotype—makes the evolution of these ecologically and medicinally important compounds interesting and experimentally tractable. Trichomes of tomato and other nightshade family plants produce structurally diverse protective compounds termed acylsugars. While cultivated tomato (Solanum lycopersicum) strictly accumulates acylsucroses, the South American wild relative Solanum pennellii produces copious amounts of acylglucoses. Genetic, transgenic, and biochemical dissection of the S. pennellii acylglucose biosynthetic pathway identified a trichome gland cell–expressed invertase-like enzyme that hydrolyzes acylsucroses (Sopen03g040490). This enzyme acts on the pyranose ring–acylated acylsucroses found in the wild tomato but not on the furanose ring–decorated acylsucroses of cultivated tomato. These results show that modification of the core acylsucrose biosynthetic pathway leading to loss of furanose ring acylation set the stage for co-option of a general metabolic enzyme to produce a new class of protective compounds.

Acylsugars are insecticidal plant specialized metabolites produced in the Solanaceae (nightshade family). Despite having simple constituents, these compounds are unusually structurally diverse. Their structural variations in phylogenetically closely related species enable comparative biochemical approaches to understand acylsugar biosynthesis and pathway diversification. Thus far, varied enzyme classes contributing to their synthesis were characterized in cultivated and wild tomatoes, including from core metabolism-isopropylmalate synthase (Leu) and invertase (carbon)-and a group of evolutionarily related BAHD acyltransferases known as acylsucrose acyltransferases. Gene duplication and neofunctionalization of these enzymes drove acylsugar diversification both within and beyond tomato. The broad set of evolutionary mechanisms underlying acylsugar diversity in Solanaceae make this metabolic network an exemplar for detailed understanding of the evolution of metabolic form and function.

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Three AtHsp90 isoforms, cytosolic AtHsp90.2, chloroplast-located AtHsp90.5, and endoplasmic reticulum (ER)-located AtHsp90.7, were characterized by constitutive overexpressing their genes in Arabidopsis thaliana. Both types of the transgenic plants overexpressing cytosolic and organellar AtHsp90s showed reduced tolerance to salt and drought stresses with lower germination rates and fresh weights, but improved tolerance to high concentration of Ca(2+) comparing with the wild type plants. Transcriptional analysis of ABA-responsive genes, RD29A, RD22 and KIN2 under salt and drought stresses, indicated that the induction expression of these genes was delayed by constitutive overexpression of cytosolic AtHsp90.2, but was hardly affected by that of organellar AtHsp90.5 and AtHsp90.7. These results implied that Arabidopsis different cellular compartments-located Hsp90s in Arabidopsis might be involved in abiotic stresses by different functional mechanisms, probably through ABA-dependent or Ca(2+) pathways, and proper homeostasis of Hsp90 was critical for cellular stress response and/or tolerance in plants.

SignificanceSpecialized metabolites are critical for plant–environment interactions, e.g., attracting pollinators or defending against herbivores, and are important sources of plant-based pharmaceuticals. However, it is unclear what proportion of enzyme-encoding genes play a role in specialized metabolism (SM) as opposed to general metabolism (GM) in any plant species. This is because of the diversity of specialized metabolites and the considerable number of incompletely characterized pathways responsible for their production. In addition, SM gene ancestors frequently played roles in GM. We evaluate features distinguishing SM and GM genes and build a computational model that accurately predicts SM genes. Our predictions provide candidates for experimental studies, and our modeling approach can be applied to other species that produce medicinally or industrially useful compounds.