Opportunistic emissions of volatile isoprenoids

Isoprene, monoterpenes and sesquiterpenes are synthesized and emitted by some plant species, but not all plant species have this ability. These volatile, nonessential isoprenoid compounds share the same biochemical precursors as larger essential isoprenoids such as gibberellic acids and carotenoids. They have many protective and ecological functions for the plant species that produce them, but plant species that do not produce these compounds also grow and reproduce successfully. Here, we develop an 'opportunist hypothesis' suggesting that (i) volatile isoprenoid production takes advantage of dimethylallyl diphosphate (DMAPP) and its isomer isopentenyl diphosphate (IPP), which are synthesized primarily to produce essential isoprenoids, and (ii) conditions affecting synthesis of the higher isoprenoids will affect the production and emission of volatile isoprenoids.     

Seed supply, recruitment, and assembly: quantifying relative seed and establishment limitation in a plant community context

There is a growing consensus that the relative constraints of seed limitation and establishment limitation in recruitment strongly influence abundance patterns in plant communities. Although these constraints have direct relevance to coexistence, most investigations utilize a seed addition approach that offers limited insight into these dynamics. Here we report the results of an assembly experiment with annual plant species from California grasslands to examine how propagule pool characteristics (dominant species abundance, functional diversity) influence establishment and seed limitation (density independence and density dependence across a gradient of seed supply) for each species, as well as how these constraints affect community diversity. Species were predominantly colimited by seed and establishment constraints, exhibiting saturating recruitment functions with increased seed supply. Consistent with competition-colonization trade-off predictions, recruitment constraints often depended on the degree of seed limitation of the competitive dominant, Brassica nigra; diversity was greatest in communities where Brassica was seed limited. Functional similarity within the propagule pool did not affect recruitment across a range of seed supply; likewise, functional diversity of the propagule pool was not related to community diversity. We conclude that seed limitation of the dominant species rather than niche similarity influences interspecific competition for safe sites and scales up to affect community-level diversity.     

Seedling establishment and life history trade-offs in alpine plants

Seedling establishment is central to population maintenance for nonclonal plant species. Plants with low recruitment rates are expected to have high survival rates, and life history theory indicates there should be a single curve for the trade-off between recruitment and mortality that applies to most or all plant species. Alpine perennials are thought to have extraordinarily low recruitment rates because of the harsh environment, but the importance of recruitment in the life history of these plants is unknown. Two alpine cushion plant species, Minuartia obtusiloba and Paronychia pulvinata, were used to (1) determine the role of recruitment in population maintenance and (2) determine whether the fecundity/mortality trade-off for these alpine plants falls on or off of the curve for other perennial plant species. Using size-based population projection matrices, we determined that the life history of Minuartia and Paronychia emphasizes recruitment less than that of any other nonclonal species in a literature survey. Estimated maximum life spans of these two species are 200 and 324 yr, respectively, and a regression with other perennial species from the literature indicated that the relationship between fecundity and mortality in these alpine species is consistent with the predicted trade-off curve for perennial species from other environments.     

Multiple roles of ADP-ribosylation factor 1 in plant cells include spatially regulated recruitment of coatomer and elements of the Golgi matrix

Recent evidence indicates that ADP-ribosylation factor 1 (ARF1) carries out multiple roles in plant cells that may be independent from the established effector complex COPI. To investigate potential COPI-independent functions, we have followed the dynamics of ARF1 and a novel putative effector, the plant golgin GRIP-related ARF-binding domain-containing Arabidopsis (Arabidopsis thaliana) protein 1 (GDAP1) in living plant cells. We present data that ascribe a new role to ARF1 in plant cell membrane traffic by showing that the GTPase functions to recruit GDAP1 to membranes. In addition, although ARF1 appears to be central to the recruitment of both COPI components and the golgin, we have established a different subcellular distribution of these ARF1 effectors. Live cell imaging demonstrates that GDAP1 and COPI are distributed on Golgi membranes. However, GDAP1 is also found on ARF1-labeled structures that lack coatomer, suggesting that the membrane environment, rather than ARF1 alone, influences the differential recruitment of ARF1 effectors. In support of this hypothesis, fluorescence recovery after photobleaching analyses demonstrated that GDAP1 and COPI have different kinetics on membranes during the cycle of activation and inactivation of ARF1. Therefore, our data support a model where modulation of the cellular functions of ARF1 in plant cells encompasses not only the intrinsic activities of the effectors, but also differential recruitment onto membranes that is spatially regulated.     

Lowland boreal forests characterization in Algonquin Provincial Park relative to beaver (Castor canadensis) foraging and edaphic factors

Beaver (Caster canadensis) foraging and edaphic conditions can modify the vegetational characteristics of woody plant community in lowland boreal forests. Effective management of these areas requires an understanding of the relative contribution of these factors in shaping the woody plant community structure. Our objective was to quantify the effects of herbivory by beavers and edaphic conditions on woody plant community organization of lowland boreal forests surrounding beaver ponds. Woody vegetation and soils were sampled at 15 ponds occupied by beavers and one other pond abandoned by them in southern Algonquin Park, Ontario. We measured spatial variation in plant diversity, foraging rates and sapling recruitment of trees and shrubs along gradients of beaver foraging intensity and soil moisture, P, K, Mg, and pH. Beavers fed preferentially on a small number of deciduous species and the number of cut stems declined sharply with increasing distance from ponds. Conifers increased in relative dominance to deciduous species in the presence of beavers. Plant species richness and stem and basal area diversity peaked at intermediate distances (about 25 m) from ponds. Sapling recruitment by non-preferred species was positively related to foraging intensity. Total stem abundance and basal area and sapling recruitment by four preferred species (Populus tremuloides, Acer rubrum, Acer saccharum and Corylus cornuta) were negatively related to foraging intensity. However, by including Alnus rugosa and Salix bebbiana (also preferred by beavers) these patterns changed, becoming positively related to foraging intensity. There was also a pronounced gradient in soil moisture, which also decreased with distance from ponds. The other measured edaphic variables did not vary consistently with distance from ponds. Sapling recruitment in mesic versus xeric species varied consistently with hydrid conditions along the moisture gradient, such that variation in moisture also could produce the observed pattern of plant diversity. Diversity patterns changed three years after beaver abandonment of a pond, though sapling recruitment patterns in preferred and non-preferred species around the abandoned pond were similar to the occupied ponds. These observations suggest spatial variation in woody plant richness and diversity could be determined by combined effects of both herbivory (disturbance by beavers) and variable responses of different species to edaphic conditions.     

Importance of animal and plant traits for fruit removal and seedling recruitment in a tropical forest

The traits of animals and plants influence their interaction networks, but the significance of species' traits for the resulting ecosystem functions is poorly understood. A crucial ecosystem function in the tropics is seed dispersal by animals. While the importance of species' traits for structuring plant–frugivore networks is supported by a number of studies, no study has so far identified the functional traits determining the subsequent processes of fruit removal and seedling recruitment. Here, we conducted a comprehensive field study on fruit removal by frugivorous birds and seedling recruitment along an elevational gradient in the Colombian Andes. We measured morphological traits of birds (body mass, bill width, Kipp's index) and plants (plant height, crop mass, fruit width and seed mass) which we expected to be related to fruit removal and seedling recruitment. We tested 1) which bird and plant traits influence fruit removal, and 2) whether network metrics at plant species level, functional identities of frugivores (community‐based mean trait values) and/or plant traits were the main determinants of seedling recruitment. We found that large‐bodied bird species contributed more to fruit removal than small‐bodied bird species and that small‐sized fruits were more frequently removed than large‐sized fruits. Small plant species and plants with heavy seeds recruited more seedlings than did large plants and plants with light seeds. Network metrics and functional identities of seed dispersers were unrelated to seedling recruitment. Our findings have two important implications. First, large birds are functionally more important than small birds in tropical seed‐removal networks. Second, the detected tradeoff between fruit size and seed mass in subsequent recruitment processes suggests that the adaptability of forest plant communities to a loss of large frugivores is limited by life‐history constraints. Hence, the protection of large‐bodied frugivores is of primary importance for the maintenance of diverse tropical plant communities.     

Seedling emergence responds to both seed source and recruitment site climates: a climate change experiment combining transplant and gradient approaches

Seedling recruitment allows genetic recombination and production of dispersal units. Both the climate experienced by the source populations (seed source effect) and the weather experienced by the seeds during germination and seedling emergence (recruitment site effects) are important for seedling recruitment. Separating these effects in the field is essential to assess potential climate change impacts on plant population. We combine experimental seed transplant and gradient analyses to separate the effects of seed source and recruitment site temperature and precipitation for the seedling emergence of two alpine/lowland species pairs (Viola biflora/Viola palustris, Veronica alpina/Veronica officinalis). Combining these approaches allows us to compare local responses versus responses along environmental gradients, but also tests for local adaptation and/or pre-conditioning effects (adaptive seedling emergence responses). Veronica officinalis emergence increased with increasing seed source temperature in both the experimental and the gradient approaches, and showed adaptive seedling emergence. Viola biflora, Viola palustris and Veronica alpina emergence decreased with recruitment site temperature in both approaches. Both Violas emergences increased with recruitment site precipitation, in both approaches for the alpine violet, and in the gradient approach for lowland one. Emergence was primarily affected by the environment of the recruitment site, whereas seed source climate and adaptive seedling emergence impacted recruitment in only one of our species. The responses to recruitment site temperatures were negative, whereas the response to seed source temperature was positive. Ignoring the distinctions between these different mechanisms can lead to erroneous conclusions regarding potential climate change impacts on plant recruitment.     

Spicing up restoration: can chili peppers improve restoration seeding by reducing seed predation?

Seed predation by rodents presents a significant barrier to native plant recruitment and can impede restoration seeding efforts. In nature, some plants contain secondary defense compounds that deter seed predators. If these natural defense compounds can be applied to unprotected seeds to inhibit rodent granivores, this approach could improve restoration seeding. Capsaicin is the active ingredient in chili pepper (Capsicum spp.) seeds that creates the burning sensation associated with human consumption of hot peppers. This compound has a similar effect on other mammals and is believed to have evolved as a deterrent to rodent seed predators. We used seed‐coating techniques to attach powder ground from Bhut Jolokia (Capsicum chinense) peppers to native plant seeds and evaluated the efficacy of these seed coatings for deterring rodent seed predation and enhancing native plant recruitment using laboratory and field experiments. Laboratory feeding trials demonstrated that native deer mice (Peromyscus maniculatus) consumed far fewer pepper‐coated seeds compared to untreated control seeds. Field seed‐addition experiments consistently demonstrated that rodent seed predation reduced native plant recruitment over the 4‐year study. Coating techniques used in the first 3 years were not persistent enough to reduce rodent seed predation effects on plant recruitment. However, a more persistent coating applied in conjunction with late‐winter sowing negated rodent seed predation effects on recruitment in year 4. Our results demonstrate that coating seeds with natural plant defense compounds may provide an effective, economical way to improve the efficacy of plant restoration by deterring seed predation by ubiquitous rodent granivores.     

Caspase-containing complexes in the regulation of cell death and inflammation

Caspases are a family of cysteine proteases that are essential in the initiation and execution of apoptosis and the proteolytic maturation of inflammatory cytokines such as IL-1beta and IL-18. Caspases can be subdivided into those that have a large prodomain and those that have not. In general, apoptotic and inflammatory signalling pathways are initiated when large-prodomain caspases are recruited to large protein complexes via homotypic interactions involving death domain folds. The formation of these specialised multimeric platforms involves three major functions: (1) the sensing of cellular stress, damage, infection or inflammation; (2) multimerisation of the platform; and (3) recruitment and conformational activation of caspases. In this overview we discuss the complexes implicated in the regulation of cell death and inflammatory processes such as the death-inducing signalling complex (DISC), the apoptosome, the inflammasomes and the PIDDosome. We describe their sensing functions, compositions and functional outcomes. Inhibitory protein families such as FLIPs and CARD-only proteins prevent the recruitment of caspases in these sensing complexes, avoiding inappropriate initiation of cell death or inflammation.     

Restoration of a species‐rich flood meadow by topsoil removal and diaspore transfer with plant material

Abstract. In previous studies, limited dispersal was revealed to be the main obstacle to restoration of species‐rich flood‐meadows along the northern Upper Rhine in Germany. To overcome dispersal limitation we transferred freshly mown plant material from species‐rich sources to a restoration site on a former arable field. Before plant material application, topsoil was removed to accelerate nutrient impoverishment and create favourable conditions for seedling recruitment. Topsoil removal led to a drastic reduction in organic matter and essential mineral nutrients to the level of target communities (P) or even below (N, K). At a removal depth of 30 cm content of the soil seed bank that comprised exclusively of annual arable weeds, ruderals and some common grassland species, declined by 60 ‐ 80%, while at a removal depth of 50 cm the seed bank was almost completely eliminated. With few exceptions, all species recorded in source plant material were found established at the restoration site. However, the overall correlation between seed content in plant material and establishment success was not very high. Vegetation development at the restoration site was characterized by a rapid decline in arable weeds and ruderals, while resident grassland species and species transferred with plant material increased rapidly from the third year onwards. After four years as many as 102 species were established that could be exclusively attributed to plant material transfer, among them many rare and highly endangered plants. Establishment of species from plant material was most successful in regularly flooded plots, due to the suppression of competitors as well as the creation of favourable moisture conditions for seedling emergence. Diaspore transfer with plant material proved to be an extremely successful method in restoring species‐rich grassland. However, high quality of plant material and suitable site conditions with low competition in early stages of succession seem to be essential prerequisites.     

hSSB1 rapidly binds at the sites of DNA double-strand breaks and is required for the efficient recruitment of the MRN complex

hSSB1 is a newly discovered single-stranded DNA (ssDNA)-binding protein that is essential for efficient DNA double-strand break signalling through ATM. However, the mechanism by which hSSB1 functions to allow efficient signalling is unknown. Here, we show that hSSB1 is recruited rapidly to sites of double-strand DNA breaks (DSBs) in all interphase cells (G1, S and G2) independently of, CtIP, MDC1 and the MRN complex (Rad50, Mre11, NBS1). However expansion of hSSB1 from the DSB site requires the function of MRN. Strikingly, silencing of hSSB1 prevents foci formation as well as recruitment of MRN to sites of DSBs and leads to a subsequent defect in resection of DSBs as evident by defective RPA and ssDNA generation. Our data suggests that hSSB1 functions upstream of MRN to promote its recruitment at DSBs and is required for efficient resection of DSBs. These findings, together with previous work establish essential roles of hSSB1 in controlling ATM activation and activity, and subsequent DSB resection and homologous recombination (HR).     

Arbuscular mycorrhizal fungi as support systems for seedling establishment in grassland

Recruitment of new seedlings into the vegetation is essential for maintaining species rich plant communities. Hence it is of pivotal importance to understand factors determining seedling recruitment. Here it is tested whether arbuscular mycorrhizal fungi (AMF) promote seedling recruitment in perennial grassland communities. Seeds of four plant species (two grasses and two forbs) were added to patches within 1‐year old grassland microcosms that were inoculated with different AMF taxa or to control microcosms that were not inoculated. The seedlings grew larger and obtained more phosphorus when AMF were present. Moreover, the seedlings obtained different amounts of phosphorus in microcosms inoculated with different AMF taxa. The results indicate that AMF promote seedling establishment by integrating emerging seedlings into extensive hyphal networks and by supplying nutrients to the seedlings. AMF, thus, act as a symbiotic support system that promotes seedling establishment and reduces recruitment limitation in grassland.     

Diversity of essential oil glands of clary sage (Salvia sclarea L., Lamiaceae)

The Lamiaceae is rich in aromatic plant species. Most of these species produce and store essential oils in specialised epidermal oil glands, which are responsible for their specific flavour. Two types of glands producing essential oil and possessing different morphological structure can be found in Salvia sclarea : peltate and capitate glands. The content of single oil glands from different positions on the plant (corolla, calyx and leaf) were sampled using an SPME fibre and analysed by gas chromatography in order to study variability of the essential oil composition. It was found that the composition of terpenoids is quite variable within an individual plant. Capitate oil glands mainly produce three essential oil compounds: the monoterpenes linalool and linalyl acetate, and the diterpene sclareol. Peltate oil glands, however, accumulate noticeable concentrations of sesquiterpenes and an unknown compound (m/z = 354). Furthermore, the oil composition varies within each gland type according to the plant organ. Linalool and linalyl acetate are characteristic substances of flowers, whereas the sesquiterpenes occur in higher proportions in leaves. Even within one gland type on a single leaf, the chemical variability is exceedingly high.     

Molecular and biochemical characterization of 2-hydroxyisoflavanone dehydratase. Involvement of carboxylesterase-like proteins in leguminous isoflavone biosynthesis

Isoflavonoids are ecophysiologically active secondary metabolites of the Leguminosae and known for health-promoting phytoestrogenic functions. Isoflavones are synthesized by 1,2-elimination of water from 2-hydroxyisoflavanones, the first intermediate with the isoflavonoid skeleton, but details of this dehydration have been unclear. We screened the extracts of repeatedly fractionated Escherichia coli expressing a Glycyrrhiza echinata cDNA library for the activity to convert a radiolabeled precursor into formononetin (7-hydroxy-4'-methoxyisoflavone), and a clone of 2-hydroxyisoflavanone dehydratase (HID) was isolated. Another HID cDNA was cloned from soybean (Glycine max), based on the sequence information in its expressed sequence tag library. Kinetic studies revealed that G. echinata HID is specific to 2,7-dihydroxy-4'-methoxyisoflavanone, while soybean HID has broader specificity to both 4'-hydroxylated and 4'-methoxylated 2-hydroxyisoflavanones, reflecting the structures of isoflavones contained in each plant species. Strikingly, HID proteins were members of a large carboxylesterase family, of which plant proteins form a monophyletic group and some are assigned defensive functions with no intrinsic catalytic activities identified. Site-directed mutagenesis with soybean HID protein suggested that the characteristic oxyanion hole and catalytic triad are essential for the dehydratase as well as the faint esterase activities. The findings, to our knowledge, represent a new example of recruitment of enzymes of primary metabolism during the molecular evolution of plant secondary metabolism.     

Mutagenicity of plant flavonoids: structural requirements for mutagenic activity in Salmonella typhimurium.

40 compounds structurally related to the plant flavonol quercetin were tested for mutagenic activity in Salmonella typhimurium strain TA98. 10 flavonols, quercetin, myricetin, rhamnetin, galangin, kaempferol, tamarixetin, morin, 3'-O-methylquercetin, 7,4'-di-O-methylquercetin and 5,7-di-O-methyl-quercetin, exhibited unequivocal mutagenic activity. 4 compounds, quercetin, myricetin, rhamnetin and 5,7-di-O-methylquercetin, were active without metabolic activation, although metabolic activation markedly enhanced their activity. All 4 have free hydroxyl groups at the 3' and 4' positions of the B ring. The other active compounds required an in vitro rat-liver metabolizing system for significant activity. Structural features which appear essential for mutagenic activity in this strain are a basic flavanoid ring structure with (1) a free hydroxyl group at the 3 position, (2) a double bond at the 2, 3 position, (3) a keto group at the 4 position, and (4) a structure which permits the proton of the 3-hydroxyl group to tautomerise to a 3-keto compound. The data are consistent with the requirement for a B ring structure that permits oxidation to quininoid intermediates. Free hydroxyl groups in the B ring are not essential for activity if a rat-liver metabolic activating system is employed. Data from 12 compounds which differ only at the essential sites described above indicate that the structural requirements for mutagenicity in strain TA100 are the same as those for activity in strain TA98. Based on the above structural requirements, a metabolic pathway for flavonol activation to DNA-reactive species is proposed.     

Reliability of macaques as seed dispersers

Seed dispersal is an ecological process crucial for forest regeneration and recruitment. To date, most studies on frugivore seed dispersal have used the seed dispersal effectiveness framework and have documented seed-handling mechanisms, dispersal distances and the effect of seed handling on germination. In contrast, there has been no exploration of “disperser reliability” which is essential to determine if a frugivore is an effective disperser only in particular regions/years/seasons or across a range of spatio-temporal scales. In this paper, we propose a practical framework to assess the spatial reliability of frugivores as seed dispersers. We suggest that a frugivore genus would be a reliable disperser of certain plant families/genera if: (a) fruits of these plant families/genera are represented in the diets of most of the species of that frugivore, (b) these are consumed by the frugivore genus across different kinds of habitats, and (c) these fruits feature among the yearly staples and preferred fruits in the diets of the frugivore genus. Using this framework, we reviewed frugivory by the genus Macaca across Asia to assess its spatial reliability as seed dispersers. We found that the macaques dispersed the seeds of 11 plant families and five plant genera including at least 82 species across habitats. Differences in fruit consumption/preference between different groups of macaques were driven by variation in plant community composition across habitats. We posit that it is essential to maintain viable populations of macaques across their range and keep human interventions at a minimum to ensure that they continue to reliably disperse the seeds of a broad range of plant species in the Anthropocene. We further suggest that this framework be used for assessing the spatial reliability of other taxonomic groups as seed dispersers.     

Synchronized reproduction promotes species coexistence through reproductive facilitation

Theories for species coexistence often emphasize niche differentiation and temporal segregation of recruitment to avoid competition. Recent work on mutualism suggested that plant species sharing pollinators provide mutual facilitation when exhibit synchronized reproduction. The facilitation on reproduction may enhance species persistence and coexistence. Theoretical ecologists paid little attention to such indirect mutualistic systems by far. We propose a new model for a two-species system using difference equations. The model focuses on adult plants and assumes no resource competition between these well-established individuals. Our formulas include demographic parameters, such as mortality and recruitment rates, and functions of reproductive facilitation. Both recruitment and facilitation effects reach saturation levels when flower production is at high levels. We conduct mathematical analyses to assess conditions of coexistence. We establish demographical conditions permitting species coexistence. Our analyses suggest a “rescue” effect from a “superior” species to a “weaker” species under strong recruitment enhancement effect when the later is not self-sustainable. The facilitation on rare species may help to overcome Allee effect.     

Mitogen-activated protein kinase signaling in plant-interacting fungi: distinct messages from conserved messengers

Mitogen-activated protein kinases (MAPKs) are evolutionarily conserved proteins that function as key signal transduction components in fungi, plants, and mammals. During interaction between phytopathogenic fungi and plants, fungal MAPKs help to promote mechanical and/or enzymatic penetration of host tissues, while plant MAPKs are required for activation of plant immunity. However, new insights suggest that MAPK cascades in both organisms do not operate independently but that they mutually contribute to a highly interconnected molecular dialogue between the plant and the fungus. As a result, some pathogenesis-related processes controlled by fungal MAPKs lead to the activation of plant signaling, including the recruitment of plant MAPK cascades. Conversely, plant MAPKs promote defense mechanisms that threaten the survival of fungal cells, leading to a stress response mediated in part by fungal MAPK cascades. In this review, we make use of the genomic data available following completion of whole-genome sequencing projects to analyze the structure of MAPK protein families in 24 fungal taxa, including both plant pathogens and mycorrhizal symbionts. Based on conserved patterns of sequence diversification, we also propose the adoption of a unified fungal MAPK nomenclature derived from that established for the model species Saccharomyces cerevisiae. Finally, we summarize current knowledge of the functions of MAPK cascades in phytopathogenic fungi and highlight the central role played by MAPK signaling during the molecular dialogue between plants and invading fungal pathogens.     

Jump‐starting coastal wetland restoration: a comparison of marsh and mangrove foundation species

During coastal wetland restoration, foundation plant species are critical in creating habitat, modulating ecosystem functions, and supporting ecological communities. Following initial hydrologic restoration, foundation plant species can help stabilize sediments and jump‐start ecosystem development. Different foundation species, however, have different traits and environmental tolerances. To understand how these traits and tolerances impact restoration trajectories, there is a need for comparative studies among foundation species. In subtropical and tropical climates, coastal wetland restoration practitioners can sometimes choose between salt marsh and/or mangrove foundation species. Here, we compared the early life history traits and environmental tolerances of two foundation species: (1) a salt marsh grass (Spartina alterniflora) and (2) a mangrove tree (Avicennia germinans). In an 18‐month study of a recently restored coastal wetland in southeastern Louisiana (USA), we examined growth and survival along an elevation gradient and compared expansion and recruitment rates. We found that the rapid growth, expansion, and recruitment rates of the salt marsh grass make it a better species for quickly establishing ecological structure at suitable elevations. The slower growth, limited expansion, and lower recruitment of the mangrove species show its restricted capacity for immediate structural restoration, especially in areas where it co‐occurs with perennial salt marsh species. Our findings suggest that the structural attributes needed in recently restored areas can be achieved sooner using fast‐growing foundation species. Following salt marsh grass establishment, mangroves can then be used to further assist ecosystem development. This work highlights how appropriate foundation species can help jump‐start ecosystem development to meet restoration objectives.     

Terpenoid biomaterials

Terpenoids (isoprenoids) encompass more than 40 000 structures and form the largest class of all known plant metabolites. Some terpenoids have well-characterized physiological functions that are common to most plant species. In addition, many of the structurally diverse plant terpenoids may function in taxonomically more discrete, specialized interactions with other organisms. Historically, specialized terpenoids, together with alkaloids and many of the phenolics, have been referred to as secondary metabolites. More recently, these compounds have become widely recognized, conceptually and/or empirically, for their essential ecological functions in plant biology. Owing to their diverse biological activities and their diverse physical and chemical properties, terpenoid plant chemicals have been exploited by humans as traditional biomaterials in the form of complex mixtures or in the form of more or less pure compounds since ancient times. Plant terpenoids are widely used as industrially relevant chemicals, including many pharmaceuticals, flavours, fragrances, pesticides and disinfectants, and as large-volume feedstocks for chemical industries. Recently, there has been a renaissance of awareness of plant terpenoids as a valuable biological resource for societies that will have to become less reliant on petrochemicals. Harnessing the powers of plant and microbial systems for production of economically valuable plant terpenoids requires interdisciplinary and often expensive research into their chemistry, biosynthesis and genomics, as well as metabolic and biochemical engineering. This paper provides an overview of the formation of hemi-, mono-, sesqui- and diterpenoids in plants, and highlights some well-established examples for these classes of terpenoids in the context of biomaterials and biofuels.