Characterization of <Emphasis Type="Italic">SpAPETALA3</Emphasis> and <Emphasis Type="Italic">SpPISTILLATA</Emphasis>, B class floral identity genes in <Emphasis Type="Italic">Spinacia oleracea</Emphasis>, and their relationship to sexual dimorphism

Floral organ identity B class genes are generally recognized as being required for development of petals and stamens in angiosperm flowers. Spinach flowers are distinguished in their complete absence of petals in both sexes, and the absence of a developed stamen whorl in female flowers. As such, we hypothesized that differential expression of B class floral identity genes is integral to the sexual dimorphism in spinach flowers. We isolated two spinach orthologs of Arabidopsis B class genes by 3 and 5 RACE. Homology assignments were tested by comparisons of percent amino acid identities, searches for diagnostic consensus amino acid residues, conserved motifs, and phylogenetic groupings. In situ hybridization studies demonstrate that both spinach B class genes are expressed throughout the male floral meristem in early stages, and continue to be expressed in sepal primordia in reduced amounts at later stages of development. They are also highly expressed in the third whorl primordia when they arise and continue to be expressed in these tissues through the development of mature anthers. In contrast, neither gene can be detected in any stage in female flowers by in situ analyses, although northern blot experiments indicate low levels of SpAP3 within the inflorescence. The early, strong expressions of both B class floral identity genes in male floral primordia and their absence in female flowers demonstrate that B class gene expression precedes the origination of third whorl primordia (stamen) in males and is associated with the establishment of sexual floral dimorphism as it initiates in the first (sepal) whorl. These observations suggest that regulation of B class floral identity genes has a role in the development of sexual dimorphism and dioecy in spinach rather than being a secondary result of organ abortion.Electronic Supplementary Material Supplementary material is available for this article at Edited by G. Jürgens     

The floral volatile,methyl benzoate,from snapdragon (<Emphasis Type="Italic">Antirrhinum majus</Emphasis>) triggers phytotoxic effects in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Previously it has been shown that the floral scent of snapdragon flowers consists of a relatively simple mixture of volatile organic compounds (VOCs). These compounds are thought to be involved in the attraction of pollinators; however, little is known about their effect on other organisms, such as neighboring plants. Here, we report that VOCs from snapdragon flowers inhibit Arabidopsis root growth. Out of the three major snapdragon floral volatiles, myrcene, (E)-β-ocimene, and methyl benzoate (MB), MB was found to be primarily responsible for the inhibition of root growth. Ten micromoles MB reduced root length by 72.6%. We employed a microarray approach to identify the MB target genes in Arabidopsis that were responsible for the root growth inhibition phenotype in response to MB. These analyses showed that MB treatment affected 1.33% of global gene expression, including cytokinin, auxin and other plant-hormone-related genes, and genes related to seed germination processes in Arabidopsis. Accordingly, the root growth of cytokinin (cre1) and auxin (axr1) response mutants was less affected than that of the wild type by the volatile compound: roots of the treated mutants were reduced by 45.1 and 56.2%, respectively, relative to untreated control mutants. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Pleiotropic effects associated with an allele enabling the flea beetle <Emphasis Type="Italic">Phyllotreta nemorum </Emphasis>to use <Emphasis Type="Italic">Barbarea vulgaris</Emphasis> as a host plant

In the Danish region of Kværkeby, a mutation in an, as yet, unknown single autosomal gene has resulted in a dominant resistance (R-) allele in the flea beetle Phyllotreta nemorum L. (Coleoptera: Chrysomelidae: Alticinae). It enables the beetle to overcome the defences of Barbarea vulgaris ssp. arcuata (Opiz.) Simkovics G-type (Brassicaceae) and use it as a host plant. In this study, we investigated the pleiotropic effects associated with the presence of this particular R-allele in female P. nemorum. These females had the R-allele backcrossed into the genetic background of non-resistant beetles. The effects were investigated under both favourable and stressful conditions (cold shock). The presence of the R-allele in a non-resistant genetic background caused a very high mortality in resistant individuals during the early stages of development under both conditions, but it did not affect the adult life-history traits longevity, body size and fecundity, under both conditions. Regardless of temperature treatment, resistant females in general were found to lay significantly more eggs. Developmental stability, as measured by tibia length fluctuating asymmetry, was not correlated with overall developmental stress in this study.     

Fruit abortion in the Chihuahuan-Desert endemic cactus <Emphasis Type="Italic">Opuntia microdasys</Emphasis>

Resource and pollen limitation, as well as pollen/ovule incompatibility, have been proposed as causes to explain fruit abortion. To assess whether abortion in Opuntia microdasys was due to resource and/or pollen limitation and could therefore be reversed fruit set and seed set were studied using controlled pollination experiments on 60 plants that had been randomly assigned a combination of watering and fertilization treatments. On the other hand, to test whether fruit abortion was irreversible, due to pollen/ovule incompatibility, we examined the reproductive biology of the species. This included observations on floral phenology, nectar production, flower visitors, numbers of pollen grains and ovules, and self-pollination experiments. Results showed that O. microdasys is a fully self-incompatible species and its floral biology and the activity of the main pollinator allow constant deposition of incompatible pollen onto stigmas, which may contribute to fruit abortion. Reproductive success was limited by nutrients and pollen, but the fruit set increased only by 58%, compared to 47% of the control, after the experimental addition of pollen, nutrients and water. The magnitude of pollen and resource limitation suggests that similar levels of abortion will be present in good as well as in bad years. Selfing as well as incompatibility between ramets from the same clone and between closely related plants seem plausible candidates to explain the large proportion of fruit abortion, and experimental cross pollination between genotypes identified through molecular markers are necessary to fully understand the considerable abortion rate that remains unexplained after pollen and resource addition. Interestingly, the possible reason why the abortion of energetically expensive fruits has not been eliminated by natural selection is that the aborted fruits are propagules able to root and produce new plants with the same genotype of the mother. Abortion would have a dramatic effect on cross-fertilized genotypes because they result in zero fitness, but it would have a positive effect on the fitness of the maternal genotype because a clonal offspring is produced. Evidently, the exact fitness consequences to the maternal plant will depend on the differences in survival and reproduction of these different offspring types.     

The interplay of pollination,costs of reproduction and plant size in maternal fertility limitation in perennial <Emphasis Type="Italic">Paeonia officinalis</Emphasis>

Although several factors can limit female fertility in perennial plants, rarely have they been jointly studied in a single species over several years. In this study we experimentally manipulate seed production and simultaneously analyse the potential contribution of pollen limitation, costs of reproduction and plant size to variation in seed output over a 3-year period in the perennial herb Paeonia officinalis, in southern France. Since this rare species is threatened by forest closure in many sites we also examine the causes of female fertility variation in relation to habitat closure (open habitat vs. woodland). P. officinalis has a partial self-incompatibility system and only very low ability for autonomous self pollination in the absence of pollinators. However, supplementary pollination of individual plants in three consecutive years did not significantly increase seed production above natural levels. Forest closure was associated with a decline in ovule and seed production, which again was not due to pollen limitation since supplementary pollination had no significant effect on seed set in the woodland habitat. Comparison of the maternal fertility of plants which were previously excluded from reproduction with those which were hand pollinated to maximise seed set in two previous years produced no evidence that seed production in year three is limited by costs associated with prior reproduction. Likewise, flowering probability was not related to prior seed production but was however positively related to plant size. The absence of any influence of pollen limitation or prior reproduction on seed production suggests that sub-maximal seed production in long-lived perennial herbs may be part of a size-dependent strategy that maximises life-time seed production and fitness without compromising survival.     

Florivory affects pollinator visitation and female fitness in <Emphasis Type="Italic">Nemophila menziesii</Emphasis>

While herbivory has traditionally been studied as damage to leaves, florivory – herbivory to flowers prior to seed set – can also have large effects on plant fitness. Florivory can decrease fitness directly, either through the destruction of gametes or through alterations to plant physiology during fruit set, and can also change the appearance of a flower, deterring pollinators and reducing seed set. In order to distinguish between these hypotheses, it is necessary to both damage flowers and add pollen in excess to study the effects of damage on pollen limitation. Very few studies have used this technique over the lifetime of a plant. Here I describe a series of experiments showing the effects of natural and artificial damage on reproductive success in the annual plant Nemophila menziesii (Hydrophyllaceae, sensu lato). I show that natural and artificial petal damage decreased radial symmetry relative to controls and that both types of damage deterred pollinator activity. Both naturally damaged flowers and artificially damaged flowers in the field set fewer fruit or seed relative to undamaged control flowers. Finally, in an experiment crossing artificial petal damage with pollen addition, petal damage alone over the lifetime of this plant decreased female fitness, but only after a threshold of damage was reached. The fitness effect appeared to be direct because there was no detectable effect of pollen addition on the relationship between florivory and fitness. This result implies that both damaged and undamaged plants show similar amounts of pollen limitation and suggests that pollinator-mediated effects contributed little to the negative effects of florivory on female fitness. Florivores may thus be an under-appreciated agent of selection in certain plants, although more experimental manipulation of florivory is needed to determine if it is important over a range of taxa.     

Flowering phenology and compensation for herbivory in<Emphasis Type="Italic"> Ipomopsis aggregata</Emphasis>

The mechanisms and circumstances that affect a plant's ability to tolerate herbivory are subjects of ongoing interest and investigation. Phenological differences, and the timing of flowering with respect to pollinators and pre-dispersal seed predators, may provide one mechanism underlying variable responses of plants to herbivore damage. The subalpine wildflower, Ipomopsis aggregata, grows across a wide range of elevations and, because phenology varies with elevation, phenological delays associated with elevation may affect the ability of I. aggregata to compensate for or tolerate browsing. Thus, we examined the response of I. aggregata to herbivory across an elevation gradient and addressed the interactions among phenological delays imposed by damage, elevation, pre-dispersal seed predation and pollination, on I. aggregata's compensatory response. Among high and low elevation populations in areas near the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado, we compared the responses of naturally browsed, artificially browsed (clipped), and unbrowsed (control) plants of I. aggregata. We compared responses in the date of initiation of flowering, timing of peak bloom, floral display, nectar production and sugar concentration, oviposition and fruit destruction by the pre-dispersal seed predator Hylemya sp. (Anthomyiidae), fruit production, and aboveground biomass production. Clipping had the greatest effect on reproductive success and clipped plants at high elevation exhibited the lowest tolerance for herbivory. The effects of browsing appear to be mediated by flowering phenology, and both browsing and elevation delayed flowering phenology. Time needed for regrowth delays flowering, and thus affects the overlap with seed predators and pollinators. As a result of delayed flowering, naturally browsed and clipped plants incurred lower rates of seed predation. In the absence of seed predation, plants would exhibit a lower tolerance to herbivory since naturally and artificially browsed plants had fewer fruits destroyed by Hylemya larvae. We provide additional evidence that, for populations near the RMBL, clipping and natural browsing do not have the same effect on I. aggregata plants. This may be due to the selection of larger plants by herbivores. Although under some conditions plants may tolerate browsing, in areas where the growing season is short a phenological delay imposed by damage is likely to significantly reduce plant fitness. Identifying the mechanisms that allow plants to tolerate herbivore damage will help to develop a general framework for understanding the role of tolerance in plant population and community dynamics, as well as plant-herbivore interactions.     

Prezygotic barriers to gene flow between <Emphasis Type="Italic">Taraxacum ceratophorum</Emphasis> and the invasive <Emphasis Type="Italic">Taraxacum officinale</Emphasis> (Asteraceae)

Prezygotic reproductive barriers limit interspecific gene flow between congeners. Here, I examine the strength of floral isolation and interspecific pollen-pistil barriers between an invasive apomictic, Taraxacum officinale, and the indigenous sexual alpine dandelion, Taraxacum ceratophorum. Experimental arrays of either native inflorescences or a mixture of native and exotic inflorescences were used to examine insect preference and to track movement of a pollen analog. Using hand-pollinations, conspecific and heterospecific pollen germination success on native stigmas was compared. To additionally test for interspecific pollen competition, T. ceratophorum plants received one of three possible hand-pollinations: control conspecific pollination, concomitant conspecific and heterospecific pollination (mixed), or conspecific pollen followed by heterospecific pollen 15 min later (staggered). Floral isolation was negligible as no insect preference was detected. On a presence/absence basis, florets on native inflorescences received slightly less pollen analog from heterospecific donors than from conspecific donors; however, the amount of dye particles transferred from either Taraxacum species to stigmas on recipient T. ceratophorum inflorescences was equivalent. In contrast to weak floral isolation, strong pollen germination and pollen competition barriers should reduce the potential for hybridization. Heterospecific T. officinale pollen exhibited reduced germination success on T. ceratophorum stigmas in comparison to conspecific pollen. Furthermore, a significant pollen-competition effect on the percentage of hybrid offspring was detected only when T. officinale preceded T. ceratophorum pollen by 15 min. This result indicates that conspecific pollen out-competes heterospecific pollen but further suggests that biotic and abiotic factors reducing pollen accrual rates may partially remove barriers to natural hybridization.     

Expression of <Emphasis Type="Italic">cspH</Emphasis> upon nutrient up-shift in <Emphasis Type="Italic">Salmonella enterica</Emphasis> serovar Typhimurium

The gene cspH , which encodes one of the cold-shock proteins in Salmonella enterica serovar Typhimurium, has previously been reported to be induced during early exponential phase at 37°C. In the present study, the expression of cspH upon nutrient up-shift at 37°C was investigated and found to be affected by DNA gyrase and DNA-binding protein Fis. When cells at stationary phase were subcultured into a rich medium, the mRNA level of cspH increased dramatically prior to the first cell division. However, when the cells were treated with DNA gyrase inhibitors, cspH mRNA was not induced upon nutrient up-shift. The low level of DNA superhelical density at the cspH promoter in part affected the expression of cspH mRNA in vitro. In addition, a fis-deficient strain had a lower level of cspH mRNA than the wild-type upon nutrient up-shift. Finally, a cspH–lacZ construct, in which the putative binding region for Fis was deleted in the cspH promoter, expressed a low level of LacZ, in contrast to the native cspH–lacZ construct.This revised version was published online in July 2004 with corrections to Fig. 4.     

Sequence evolution and sex-specific expression patterns of the C class floral identity gene, <Emphasis Type="Italic">SpAGAMOUS</Emphasis>, in dioecious <Emphasis Type="Italic">Spinacia oleracea</Emphasis> L

Development in dioecious cultivated spinach, Spinacia oleracea, is distinguished by the absence of alternative reproductive organ primordia in male and female flowers. Given the highly derived floral developmental program in spinach, we wished to characterize a spinach C class floral identity gene and to determine the patterns of sequence evolution as well as compare the spatial and temporal expression patterns with those of AGAMOUS. The isolated cDNA sequence clusters phylogenetically within the AGAMOUS/FARINELLI C class clade. In comparison with the SLM1 sequence from the related Silene latifolia, amino acid replacements are highly conservative and non-randomly distributed, being predominantly found in hinge regions or on exposed surfaces of helices. The spinach gene (SpAGAMOUS) appears to be exclusively expressed in reproductive tissues and not in vegetative organs. Initial expression of SpAGAMOUS is similar in male and female floral primordia. However, upon initiation of the first whorl organs, SpAGAMOUS becomes restricted to meristemic regions from which the reproductive primordia will develop. This results in an early gender-specific pattern. Thus, the spinach C class gene is differentially expressed prior to reproductive organ development and is, at least, correlated with, if not directly involved in, the sexual dimorphism in spinach.Electronic Supplementary Material Supplementary material is available for this article at     

Variation in resource limitation of plant reproduction influences natural selection on floral traits of <Emphasis Type="Italic">Asclepias syriaca</Emphasis>

The availability of both pollen and resources can influence natural selection on floral traits, but their relative importance in shaping floral evolution is unclear. We experimentally manipulated pollinator and resource (fertilizer and water) availability in the perennial wildflower Asclepias syriaca L. Nine floral traits, one male fitness component (number of pollinia removed), and two female fitness components (number of pollinia inserted and number of fruits initiated) were measured for plants in each of three treatments (unmanipulated control, decreased pollinator access, and resource supplementation). Although decreasing pollinators’ access to flowers did result in fewer pollinia inserted and removed, fruit set and phenotypic selection on floral traits via female and male fitness did not differ from the control. In contrast, resource supplementation increased fruit set, and phenotypic selection on seven out of nine floral traits was stronger via female than male fitness, consistent with the prediction that selection via female fitness would be greater when reproduction was less resource-limited. Our results support the hypothesis that abiotic resource availability can influence floral evolution by altering gender-specific selection.     

Use of <Emphasis Type="Italic">Quercus ilex</Emphasis> subsp. <Emphasis Type="Italic">ballota</Emphasis> phenological and pollen-production data for interpreting <Emphasis Type="Italic">Quercus</Emphasis> pollen curves

Although aerobiological data are often used in phenological research as an indicator of flowering, airborne pollen concentrations are influenced by a number of factors that could affect pollen curves. This paper reports on a study of various aspects of reproductive biology in Q. ilex subsp. ballota, together with environmental factors influencing pollen release and transport, with a view of achieving reliable interpretation of Quercus pollen curves in Ourense (NW Spain). Aerobiological data were recorded from 2002 to 2004 at two sites in the province of Ourense. From 1st February to the end of the flowering period, phenological observations were carried out on 19 trees from the Q. ilex subsp. ballota population found in the Ourense area. Pollen production was calculated for the same trees. The chilling and heating requirements for triggering development were also calculated. The mean flowering period lasted 11-15 days. Reduced pollen output per catkin and, especially, a reduced number of catkins per tree in 2003 and 2004, prompted a marked decline in overall pollen production. Major differences observed in Q. ilex subsp. ballota pollen curves were attributed to the considerable influence both of weather conditions during pollination and pollen production. In years with high pollen production and weather conditions favouring pollen release, Q. ilex subsp. ballota contributed almost 10% to the total Quercus pollen curve. Around 20% of the pollen trapped was captured before or after flowering periods.     

Post-pollination hybridization barriers in <Emphasis Type="Italic">Nicotiana</Emphasis> section <Emphasis Type="Italic">Alatae</Emphasis>

Nicotiana section Alatae contains eight species with variable flower sizes and morphologies. Section members readily hybridize in the glasshouse, but no hybrids have been observed in natural sympatric and parapatric populations. To investigate interspecific crossing relationships with respect to mechanisms preventing hybridization, all members of section Alatae were intercrossed in a complete diallel. We found positive correlation between the pistil length of the pollen donor and interspecific seed set relative to the conspecific cross. Pollen tube growth rate and pollen donor pistil length were positively correlated as well. Furthermore, pollen from short-pistil members of section Alatae could only grow a maximum distance proportional to, but greater than, their own pistil lengths. Our results show that pollen tube growth capacity (i.e., rate and distance), provides a hybridization barrier in long-pistil species × short-pistil species crosses. We also found another hybridization barrier not specifically related to pollen tube growth capacity in short-pistil species × long-pistil species. Taken together, these barriers can generally be described by a ‘pistil-length mismatch’ rule; in section Alatae, pollen has the most success fertilizing ovules from species with pistil lengths similar to their own. This rule could contribute to hybridization barriers in Section Alatae because the species display dramatically different pistil lengths. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Fruit production and floral traits: correlated evolution in <Emphasis Type="Italic">Govenia</Emphasis> (Orchidaceae)

The most common estimate of reproductive success in orchids is usually fruit set. Factors such as resource limitation and certain floral traits may influence reproductive success in animal-pollinated plants. Correlated evolution of reproductive success vs. seven floral traits (inflorescence length, flower number, flower distribution along inflorescence, dorsal sepal length, lateral sepal length, flower color, and column position) was studied in eight species of Govenia. Taxa represented three lineages in the genus. Independent contrasts were calculated on a phylogeny inferred from chloroplast (trnL-F IGS) DNA sequences, and a correlation test and multiple regression were then performed. Two data sets were evaluated, one including all eight species and another excluding G. utriculata, which is autogamous. The historical analyses showed that there is a correlation between reproductive success and dorsal sepal length, column position, and flower number, these correlations suggest that changes in these floral traits usually accompany evolutionary shifts in reproductive success. Multiple regression tests suggest that changes in reproductive success can be explained by shifts in flower number, inflorescence length, column position and by dorsal sepal length. When phylogeny is taken into account, our analyses showed that evolutionary shifts in these floral traits were correlated with changes in reproductive success. Evolutionary correlation between reproductive success and floral traits might be explained by the natural selection of certain floral phenotypes by pollinators.     

<Emphasis Type="Italic">Ty</Emphasis>1<Emphasis Type="Italic">/copia</Emphasis>- and <Emphasis Type="Italic">Ty</Emphasis>3<Emphasis Type="Italic">/gypsy</Emphasis>-like DNA sequences in <Emphasis Type="Italic">Helianthus </Emphasis>species

Two repeated DNA sequences isolated from a partial genomic DNA library of Helianthus annuus, p HaS13 and p HaS211, were shown to represent portions of the int gene of a Ty3 /gypsy retroelement and of the RNase-Hgene of a Ty1 /copia retroelement, respectively. Southern blotting patterns obtained by hybridizing the two probes to BglII- or DraI-digested genomic DNA from different Helianthus species showed p HaS13 and p HaS211 were parts of dispersed repeats at least 8 and 7 kb in length, respectively, that were conserved in all species studied. Comparable hybridization patterns were obtained in all species with p HaS13. By contrast, the patterns obtained by hybridizing p HaS211 clearly differentiated annual species from perennials. The frequencies of p HaS13- and p HaS211-related sequences in different species were 4.3x10(4)-1.3x10(5) copies and 9.9x10(2)-8.1x10(3) copies per picogram of DNA, respectively. The frequency of p HaS13-related sequences varied widely within annual species, while no significant difference was observed among perennial species. Conversely, the frequency variation of p HaS211-related sequences was as large within annual species as within perennials. Sequences of both families were found to be dispersed along the length of all chromosomes in all species studied. However, Ty3 /gypsy-like sequences were localized preferentially at the centromeric regions, whereas Ty1/ copia-like sequences were less represented or absent around the centromeres and plentiful at the chromosome ends. These findings suggest that the two sequence families played a role in Helianthusgenome evolution and species divergence, evolved independently in the same genomic backgrounds and in annual or perennial species, and acquired different possible functions in the host genomes.     

<Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated genetic transformation of <Emphasis Type="Italic">Perilla frutescens</Emphasis>

A reproducible plant regeneration and an Agrobacterium tumefaciens-mediated genetic transformation protocol were developed for Perilla frutescens (perilla). The largest number of adventitious shoots were induced directly without an intervening callus phase from hypocotyl explants on MS medium supplemented with 3.0 mg/l 6-benzylaminopurine (BA). The effects of preculture and extent of cocultivation were examined by assaying -glucuronidase (GUS) activity in explants infected with A. tumefaciens strain EHA105 harboring the plasmid pIG121-Hm. The highest number of GUS-positive explants were obtained from hypocotyl explants cocultured for 3 days with Agrobacterium without precultivation. Transgenic perilla plants were regenerated and selected on MS basal medium supplemented with 3.0 mg/l BA, 125 mg/l kanamycin, and 500 mg/l carbenicillin. The transformants were confirmed by PCR of the neomycin phosphotransferase II gene and genomic Southern hybridization analysis of the hygromycin phosphotransferase gene. The frequency of transformation from hypocotyls was about 1.4%, and the transformants showed normal growth and sexual compatibility by producing progenies.     

The tyrosine <Emphasis Type="Italic">O</Emphasis>-prenyltransferase SirD catalyzes <Emphasis Type="Italic">O</Emphasis>-, <Emphasis Type="Italic">N</Emphasis>-, and <Emphasis Type="Italic">C</Emphasis>-prenylations

Recently, the prenyltransferase SirD was found to be responsible for the O-prenylation of tyrosine in the biosynthesis of sirodesmin PL in Leptosphaeria maculans. In this study, the behavior of SirD towards phenylalanine/tyrosine and tryptophan derivatives was investigated. Product formation has been observed with 12 of 19 phenylalanine/tyrosine derivatives. It was shown that the alanine structure attached to the benzene ring and an electron donor, e.g., OH or NH₂, at its para-position are essential for the enzyme activity. Modifications were possible both at the side chain and the benzene ring. Enzyme products from seven phenylalanine/tyrosine derivatives were isolated and characterized by MS and NMR analyses including HSQC and HMBC and proven to be O- or N-prenylated derivatives at position C4 of the benzene rings. K _M values of six selected derivatives were found in the range of 0.10–0.68 mM. Catalytic efficiencies (K _cat/K _M ) were determined in the range of 430–1,110 s⁻¹·M⁻¹ with l-tyrosine as the best substrate. In addition, 7 of 14 tested tryptophan analogs were also accepted by SirD and converted to C7-prenylated derivatives, which was confirmed by comparison with products obtained from enzyme assays using a 7-dimethylallyltryptophan synthase 7-DMATS from Aspergillus fumigatus.