A Novel Pathway for Sesquiterpene Biosynthesis from Z,Z-Farnesyl Pyrophosphate in the Wild Tomato Solanum habrochaites

In the wild tomato Solanum habrochaites, the Sst2 locus on chromosome 8 is responsible for the biosynthesis of several class II sesquiterpene olefins by glandular trichomes. Analysis of a trichome-specific EST collection from S. habrochaites revealed two candidate genes for the synthesis of Sst2-associated sesquiterpenes. zFPS encodes a protein with homology to Z-isoprenyl pyrophosphate synthases and SBS (for Santalene and Bergamotene Synthase) encodes a terpene synthase with homology to kaurene synthases. Both genes were found to cosegregate with the Sst2 locus. Recombinant zFPS protein catalyzed the synthesis of Z,Z-FPP from isopentenylpyrophosphate (IPP) and dimethylallylpyrophosphate (DMAPP), while coincubation of zFPS and SBS with the same substrates yielded a mixture of olefins identical to the Sst2-associated sesquiterpenes, including (+)-α-santalene, (+)-endo-β-bergamotene, and (−)-endo-α-bergamotene. In addition, headspace analysis of tobacco (Nicotiana sylvestris) plants expressing zFPS and SBS in glandular trichomes afforded the same mix of sesquiterpenes. Each of these proteins contains a putative plastid targeting sequence that mediates transport of a fused green fluorescent protein to the chloroplasts, suggesting that the biosynthesis of these sesquiterpenes uses IPP and DMAPP from the plastidic DXP pathway. These results provide novel insights into sesquiterpene biosynthesis and have general implications concerning sesquiterpene engineering in plants.     

Divergent regulation of terpenoid metabolism in the trichomes of wild and cultivated tomato species

The diversification of chemical production in glandular trichomes is important in the development of resistance against pathogens and pests in two species of tomato. We have used genetic and genomic approaches to uncover some of the biochemical and molecular mechanisms that underlie the divergence in trichome metabolism between the wild species Solanum habrochaites LA1777 and its cultivated relative, Solanum lycopersicum. LA1777 produces high amounts of insecticidal sesquiterpene carboxylic acids (SCAs), whereas cultivated tomatoes lack SCAs and are more susceptible to pests. We show that trichomes of the two species have nearly opposite terpenoid profiles, consisting mainly of monoterpenes and low levels of sesquiterpenes in S. lycopersicum and mainly of SCAs and very low monoterpene levels in LA1777. The accumulation patterns of these terpenoids are different during development, in contrast to the developmental expression profiles of terpenoid pathway genes, which are similar in the two species, but they do not correlate in either case with terpenoid accumulation. However, our data suggest that the accumulation of monoterpenes in S. lycopersicum and major sesquiterpenes in LA1777 are linked both genetically and biochemically. Metabolite analyses after targeted gene silencing, inhibitor treatments, and precursor feeding all show that sesquiterpene biosynthesis relies mainly on products from the plastidic 2-C-methyl-d-erythritol-4-phosphate pathway in LA1777 but less so in the cultivated species. Furthermore, two classes of sesquiterpenes produced by the wild species may be synthesized from distinct pools of precursors via cytosolic and plastidial cyclases. However, highly trichome-expressed sesquiterpene cyclase-like enzymes were ruled out as being involved in the production of major LA1777 sesquiterpenes.     

The diverse sesquiterpene profile of patchouli, Pogostemon cablin, is correlated with a limited number of sesquiterpene synthases

Pogostemon cablin (patchouli), like many plants within the Lamiaceae, accumulates large amounts of essential oil. Patchouli oil is unique because it consists of over 24 different sesquiterpenes, rather than a blend of different mono-, sesqui- and di-terpene compounds. To determine if this complex mixture of sesquiterpenes arises from an equal number of unique sesquiterpene synthases, we developed a RT-PCR strategy to isolate and functionally characterize the respective patchouli oil synthase genes. Unexpectedly, only five terpene synthase cDNA genes were isolated. Four of the cDNAs encode for synthases catalyzing the biosynthesis of one major sesquiterpene, including a gamma-curcumene synthase, two germacrene D synthases, and a germacrene A synthase. The fifth cDNA encodes for a patchoulol synthase, which catalyzes the conversion of FPP to patchoulol plus at least 13 additional sesquiterpene products. Equally intriguing, the yield of the different in vitro reaction products resembles quantitatively and qualitatively the profile of sesquiterpenes found in patchouli oil extracted from plants, suggesting that a single terpene synthase is responsible for the bulk and diversity of terpene products produced in planta.     

The tomato terpene synthase gene family

Compounds of the terpenoid class play numerous roles in the interactions of plants with their environment, such as attracting pollinators and defending the plant against pests. We show here that the genome of cultivated tomato (Solanum lycopersicum) contains 44 terpene synthase (TPS) genes, including 29 that are functional or potentially functional. Of these 29 TPS genes, 26 were expressed in at least some organs or tissues of the plant. The enzymatic functions of eight of the TPS proteins were previously reported, and here we report the specific in vitro catalytic activity of 10 additional tomato terpene synthases. Many of the tomato TPS genes are found in clusters, notably on chromosomes 1, 2, 6, 8, and 10. All TPS family clades previously identified in angiosperms are also present in tomato. The largest clade of functional TPS genes found in tomato, with 12 members, is the TPS-a clade, and it appears to encode only sesquiterpene synthases, one of which is localized to the mitochondria, while the rest are likely cytosolic. A few additional sesquiterpene synthases are encoded by TPS-b clade genes. Some of the tomato sesquiterpene synthases use z,z-farnesyl diphosphate in vitro as well, or more efficiently than, the e,e-farnesyl diphosphate substrate. Genes encoding monoterpene synthases are also prevalent, and they fall into three clades: TPS-b, TPS-g, and TPS-e/f. With the exception of two enzymes involved in the synthesis of ent-kaurene, the precursor of gibberellins, no other tomato TPS genes could be demonstrated to encode diterpene synthases so far.     

不同番茄种质叶表次生代谢物质

多毛番茄(Solanum habrochaites)为重要的番茄种质资源, 其叶表存在大量次生代谢物质, 对多种虫害具有趋避或/和毒害作用。利用气相色谱-质谱联用(GC-MS)技术分析栽培番茄(S. lycopersicum ) 9706与3份多毛番茄(LA2329、LA1777和PI134417)材料叶表次生代谢物质。结果表明, 3份多毛番茄叶表可检测到的次生代谢物质种类和总含量均高于普通番茄, 同时多毛番茄亚种间次生代谢物质的种类和含量也存在差异。普通番茄叶表次生代谢物质为3种单萜和3种倍半萜类物质, 其中单萜和倍半萜类物质分别占次生代谢物质总量的60.3%和39.7%。多毛番茄LA2329和LA1777叶表倍半萜类物质的种类和含量较高, 有些萜类物质具有物种特异性。如LA2329中含量最高的α-姜烯, 其含量为2 409.1 μg·g^–1; LA1777中含量较高的γ-榄香烯和E-β-法尼烯, 含量分别为573.3 μg·g^–1和289.9 μg·g^–1, 在其它番茄材料中未检测到这3种倍半萜类物质。PI134417中含量最高的是月桂酸乙酯, 其含量为5 312.8 μg·g^–1, 在普通番茄中这一物质未见报道。PI134417中甲基酮类物质含量也较高, 其中2-十一烷酮和2-十三烷酮的含量分别为689.8 μg·g^–1和1 459.7 μg·g^–1。研究结果可为番茄种质资源利用和次生代谢物质开发提供理论依据。     

Characterization of four terpene synthase cDNAs from methyl jasmonate-induced Douglas-fir, Pseudotsuga menziesii

Numerous terpenoid compounds are present in copious amounts in the oleoresin produced by conifers, especially following exposure to insect or fungal pests. CDNA clones for many terpene synthases responsible for the biosynthesis of these defense compounds have been recovered from several conifer species. Here, the use of three terpene synthase sequences as heterologous probes for the discovery of related terpene synthase genes in Douglas-fir, Pseudotsuga menziesii (Mirbel) Franco (Pinaceae), is reported. Four full-length terpene synthase cDNAs were recovered from a methyl jasmonate-induced Douglas-fir bark and shoot cDNA library. These clones encode two multi-product monoterpene synthases [a (-)-alpha-pinene/(-)-camphene synthase and a terpinolene synthase] and two single-product sesquiterpene synthases [an (E)-beta-farnesene synthase and a (E)-gamma-bisabolene synthase].     

Evolution of TPS20-related terpene synthases influences chemical diversity in the glandular trichomes of the wild tomato relative Solanum habrochaites

A systematic screen of volatile terpene production in the glandular trichomes of 79 accessions of Solanum habrochaites was conducted and revealed the presence of 21 mono‐ and sesquiterpenes that exhibit a range of qualitative and quantitative variation. Hierarchical clustering identified distinct terpene phenotypic modules with shared patterns of terpene accumulation across accessions. Several terpene modules could be assigned to previously identified terpene synthase (TPS) activities that included members of the TPS‐e/f subfamily that utilize the unusual cis‐prenyl diphosphate substrates neryl diphosphate and 2z,6z‐farnesyl diphosphate. DNA sequencing and in vitro enzyme activity analysis of TPS‐e/f members from S. habrochaites identified three previously unassigned enzyme activities that utilize these cisoid substrates. These produce either the monoterpenes α‐pinene and limonene, or the sesquiterpene 7‐epizingiberene, with the in vitro analyses that recapitulated the trichome chemistry found in planta. Comparison of the distribution of S. habrochaites accessions with terpene content revealed a strong preference for the presence of particular TPS20 alleles at distinct geographic locations. This study reveals that the unusually high intra‐specific variation of volatile terpene synthesis in glandular trichomes of S. habrochaites is due at least in part to evolution at the TPS20 locus.     

Evidence of cryptic introgression in tomato (Solanum lycopersicum L.) based on wild tomato species alleles

ABSTRACT: BACKGROUND: Many beneficial traits (e.g. disease or abiotic stress resistance) have been transferred into crops through crosses with their wild relatives. The 13 recognized species of tomato (Solanum section Lycopersicon) are closely related to each other and wild species genes have been extensively used for improvement of the crop, Solanum lycopersicum L. In addition, the lack of geographical barriers has permitted natural hybridization between S. lycopersicum and its closest wild relative Solanum pimpinellifolium in Ecuador, Peru and northern Chile. In order to better understand patterns of S. lycopersicum diversity, we sequenced 47 markers ranging in length from 130 to 1200 bp (total of 24 kb) in genotypes of S. lycopersicum and wild tomato species S. pimpinellifolium, Solanum arcanum, Solanum peruvianum, Solanum pennellii and Solanum habrochaites. Several of the markers had previously been hypothesized as carrying wild species alleles within S. lycopersicum, i.e., cryptic introgressions. RESULTS: Each marker was mapped with high confidence (e < 1 x 10-30) to a single genomic location using BLASTN against tomato whole genome shotgun chromosomes (SL2.40) database. Neighbor-joining trees showed high mean bootstrap support (86.8 plus or minus 2.34%) for distinguishing red-fruited from green-fruited taxa for 38 of the markers. Hybridization and parsimony splits networks, genomic map positions of markers relative to documented introgressions, and historical origins of accessions were used to interpret evolutionary patterns at nine markers with putatively introgressed alleles. CONCLUSION: Of the 47 genetic markers surveyed in this study, four were involved in linkage drag on chromosome 9 during introgression breeding, while alleles at five markers apparently originated from natural hybridization with S. pimpinellifolium and were associated with primitive genotypes of S. lycopersicum. The positive identification of introgressed genes within crop species such as S. lycopersicum will help inform conservation and utilization of crop germplasm diversity, for example, facilitating the purging of undesirable linkage drag or the exploitation of novel, favorable alleles.     

Metabolic profiling of leaves and fruit of wild species tomato: a survey of the Solanum lycopersicum complex

The domestication of the tomato Solanum lycopersicum and associated selective pressures eventually led to the large-fruited varieties cultivated today. S. lycopersicum varieties are generally red-fruited, but display considerable variance in fruit colour intensity, shape, and quality. The increase in productivity on cultivation is, however, somewhat offset by the narrowing of the crops genetic base which leads to increased susceptibility to biotic and abiotic stresses. Since S. lycopersicum can easily be crossed with its wild species relatives, this exotic germplasm can provide a valuable source for the improvement of agriculturally important traits. A GC-MS based survey is presented here of the relative metabolic levels of leaves and fruit of S. lycopersicum and five wild species of tomato that can be crossed with it (S. pimpinellifolium, S. neorickii, S. chmielewskii, S. habrochaites, and S. pennellii). Changes in metabolite contents were identified in the wild species that are potentially important with respect to stress responses, as well as in metabolites of nutritional importance. The significance of these changes is discussed with respect to the use of the various wild species for metabolic engineering within wide breeding strategies.     

Emissions of green leaf volatiles and terpenoids from Solanum lycopersicum are quantitatively related to the severity of cold and heat shock treatments

Plant-generated volatiles constitute a sensitive signal of stress response, but quantitative relationships between the stress severity and volatile emissions have been demonstrated only for a few stresses. Among important stresses in the field, chilling and frost stress in spring and heat stress mid-season can significantly curb productivity. We studied the effects of cold and heat shock treatments on leaf photosynthesis and the emission of the volatile products of the lipoxygenase pathway (LOX, also called green leaf volatiles) and mono- and sesquiterpene emissions in tomato (Solanum lycopersicum cv. Mato) to gain quantitative insights into temperature stress-elicited volatile emissions. Both cold and heat stress treatments ranged from mild, which only weakly affected foliage photosynthesis, to severe, which almost completely inhibited photosynthesis. Under non-stressed conditions, LOX emissions were close to the detection limit, and terpene emissions were low. Both cold and heat stress led to enhancement of LOX emissions according to a switch-type response with essentially no emissions under mild stress and major emissions under severe stress. The emissions of mono- and sesquiterpenes increased gradually with the severity of stress, but cold stress resulted in higher sesquiterpene emissions at any given monoterpene emission level. We suggest that the quantitative relationships between the stress strength and emissions observed in this study provide an important means to characterize the severity of cold and heat stresses.     

Comparative genetics of hybrid incompatibility: sterility in two Solanum species crosses

The genetic basis of hybrid sterility can provide insight into the genetic and evolutionary origins of species barriers. We examine the genetics of hybrid incompatibility between two diploid plant species in the plant clade Solanum sect. Lycopersicon. Using a set of near-isogenic lines (NILs) representing the wild species Solanum pennellii (formerly Lycopersicon pennellii) in the genetic background of the cultivated tomato S. lycopersicum (formerly L. esculentum), we found that hybrid pollen and seed infertility are each based on a modest number of loci, male (pollen) and other (seed) incompatibility factors are roughly comparable in number, and seed-infertility QTL act additively or recessively. These findings are remarkably consistent with our previous analysis in a different species pair, S. lycopersicum x S. habrochaites. Data from both studies contrast strongly with data from Drosophila. Finally, QTL for pollen and seed sterility from the two Solanum studies were chromosomally colocalized, indicating a shared evolutionary history for these QTL, a nonrandom genomic distribution of loci causing sterility, and/or a proclivity of certain genes to be involved in hybrid sterility. We show that comparative mapping data can delimit the probable timing of evolution of detected QTL and discern which sterility loci likely evolved earliest among species.