Harald Meimberg

Evolutionary change from induced to constitutive expression of an indirect plant resistance

Induced plant resistance traits are expressed in response to attack and occur throughout the plant kingdom. Despite their general occurrence, the evolution of such resistances has rarely been investigated. Here we report that extrafloral nectar, a usually inducible trait, is constitutively secreted by Central American Acacia species that are obligately inhabited by ants. Extrafloral nectar is secreted as an indirect resistance, attracting ants that defend plants against herbivores. Leaf damage induces extrafloral nectar secretion in several plant species; among these are various Acacia species and other Fabaceae investigated here. In contrast, Acacia species obligately inhabited by symbiotic ants nourish these ants by secreting extrafloral nectar constitutively at high rates that are not affected by leaf damage. The phylogeny of the genus Acacia and closely related genera indicate that the inducibility of extrafloral nectar is the plesiomorphic or ‘original’ state, whereas the constitutive extrafloral nectar flow is derived within Acacia. A constitutive resistance trait has evolved from an inducible one, obviously in response to particular functional demands.

The role of adaptive trans-generational plasticity in biological invasions of plants

High‐impact biological invasions often involve establishment and spread in disturbed, high‐resource patches followed by establishment and spread in biotically or abiotically stressful areas. Evolutionary change may be required for the second phase of invasion (establishment and spread in stressful areas) to occur. When species have low genetic diversity and short selection history, within‐generation phenotypic plasticity is often cited as the mechanism through which spread across multiple habitat types can occur. We show that trans‐generational plasticity (TGP) can result in pre‐adapted progeny that exhibit traits associated with increased fitness both in high‐resource patches and in stressful conditions. In the invasive sedge, Cyperus esculentus, maternal plants growing in nutrient‐poor patches can place disproportional number of propagules into nutrient‐rich patches. Using the invasive annual grass, Aegilops triuncialis, we show that maternal response to soil conditions can confer greater stress tolerance in seedlings in the form of greater photosynthetic efficiency. We also show TGP for a phenological shift in a low resource environment that results in greater stress tolerance in progeny. These lines of evidence suggest that the maternal environment can have profound effects on offspring success and that TGP may play a significant role in some plant invasions.

Identification of a 4-coumarate:CoA ligase gene family in the moss, Physcomitrella patens

Since the early evolution of land plants from primitive green algae, phenylpropanoid compounds have played an important role. In the biosynthesis of phenylpropanoids, 4-coumarate:CoA ligase (4CL; EC 6.2.1.12) has a pivotal role at the divergence point from general phenylpropanoid metabolism to several major branch pathways. Although higher plant 4CLs have been extensively studied, little information is available on the enzymes from bryophytes. In Physcomitrella patens, we have identified a 4CL gene family consisting of four members, taking advantage of the available EST sequences and a draft sequence of the P. patens genome. The encoded proteins of three of the genes display similar substrate utilization profiles with highest catalytic efficiency towards 4-coumarate. Interestingly, the efficiency with cinnamate as substrate is in the same range as with caffeate and ferulate. The deduced proteins of the four genes share sequence identities between 78% and 86%. The intron/exon structures are pair wise similar. Pp4CL2 and Pp4CL3 each consists of four exons and three introns, whereas Pp4CL1 and Pp4CL4 are characterized each by five exons and four introns. Pp4CL1, Pp4CL2 and Pp4CL3 are expressed in both gametophore and protonema tissue of P. patens, unlike Pp4CL4 whose expression could not be demonstrated under the conditions employed. Phylogenetic analysis suggests an early evolutionary divergence of Pp4CL gene family members. Using Streptomyces coelicolor cinnamate:CoA ligase (ScCCL) as an outgroup, the P. patens 4CLs are clearly separated from the spermatophyte proteins, but are intercalated between the angiosperm 4CL class I and class II. A comparison of three P. patens subspecies from diverse geographical locations shows high sequence identities for the four 4CL isoforms.

Chemical composition of epicuticular wax crystals on the slippery zone in pitchers of five Nepenthes species and hybrids

Plants of the carnivorous genus Nepenthes efficiently trap insects in leaf pitchers, mostly employing epicuticular wax crystals on the pitcher walls to make them slippery for the prey. In the present study, the compositions and micromorphologies of the wax crystals of five Nepenthes species and hybrids were analysed in order to test whether the chemical principles underlying this ecological function are widespread within the genus. Three wax layers could be distinguished within the Nepenthes pitcher cuticles: (1) the outermost part of the crystals forming the platelets visible in standard scanning electron microscopy, (2) the bottom portion of the epicuticular wax crystals, and (3) an intracuticular wax layer. The composition of the intracuticular wax differed significantly from that of the neighbouring epicuticular layer. The compositions of corresponding wax mixtures from all five Nepenthes species and hybrids were very similar, with almost equal amounts of very long chain aldehydes and primary alcohols. While triacontanal (C30 aldehyde) was prevailing in the epicuticular crystals of Nepenthes albomarginata and Nepenthes x intermedia, Nepenthes x superba and Nepenthes x henriana were found to have especially high percentages of dotriacontanal (C32 aldehyde). Nepenthes “khasiana” had an intermediate aldehyde composition with almost equal amounts of both chain lengths.

Patterns of introduction and adaptation during the invasion of Aegilops triuncialis (Poaceae) into Californian serpentine soils.

Multiple introductions can play a prominent role in explaining the success of biological invasions. One often cited mechanism is that multiple introductions of invasive species prevent genetic bottlenecks by parallel introductions of several distinct genotypes that, in turn, provide heritable variation necessary for local adaptation. Here, we show that the invasion of Aegilops triuncialis into California, USA, involved multiple introductions that may have facilitated invasion into serpentine habitats. Using microsatellite markers, we compared the polymorphism and genetic structure of populations of Ae. triuncialis invading serpentine soils in California to that of accessions from its native range. In a glasshouse study, we also compared phenotypic variation in phenological and fitness traits between invasive and native populations grown on loam soil and under serpentine edaphic conditions. Molecular analysis of invasive populations revealed that Californian populations cluster into three independent introductions (i.e. invasive lineages). Our glasshouse common garden experiment found that all Californian populations exhibited higher fitness under serpentine conditions. However, the three invasive lineages appear to represent independent pathways of adaptation to serpentine soil. Our results suggest that the rapid invasion of serpentine habitats in California may have been facilitated by the existence of colonizing Eurasian genotypes pre‐adapted to serpentine soils.

Development of phylogenetic markers from single-copy nuclear genes for multi locus, species level analyses in the mint family (Lamiaceae).

The use of single copy nuclear markers is of increasing importance in plant phylogenetics. The generally higher level of variability compared to chloroplast DNA and the ability to use incongruence in a multilocus analysis to determine reticulation patterns makes these kinds of sequence based markers especially useful for species level investigations. However, the prevalence of gene duplication that results from the high frequency of polyploidization events during the evolution of higher plants can impede marker development especially for groups lacking model organisms. Here, we present the strategy and results of marker development for phylogenetic analysis in Micromeria, using publicly available DNA sequences and ESTs from related genera from Lamiaceae, subfamily Nepetoideae. By eliminating markers with signatures of duplication during four steps of marker development, we were able to select 19 primer pairs that resulted in orthologous products for all the species studied. This corresponds to 23% of the initial 84 primer pairs designed. Using an initial sampling of eight individuals, we tested the markers for support of phylogenetic hypotheses related to the evolution of Micromeria on the Canary Islands. While some hypotheses were supported by all markers, an east west split, with a closer relationship between the species of Tenerife and Madeira on one hand and the ones from Gran Canaria and the eastern islands on the other is supported by 12 markers but contradicted by the remaining seven. This indicates that reticulation and inter-island gene flow played a role in the evolution of Micromeria.

New Names in Old World Clinopodium: The Transfer of the Species of Micromeria Sect. Pseudomelissa to Clinopodium

Micromeria has recently been revealed polyphyletic by molecular analyses, with members of sect. Pseudomelissa placed in close relationship to Clinopodium vulgare. Morphological data suport transferring the section to Clinopodium. A list of names under Clinopodium (including 15 new combinations) is provided for the taxa hitherto included in Micromeria sect. Pseudomelissa. Three species names are typified.

Evidence for species differentiation within the Ancistrocladus tectorius complex (Ancistrocladaceae) in Southeast Asia: a molecular approach

Representatives of the genus Ancistrocladus, woody lianas of tropical Africa and Asia, contain pharmaceutically interesting alkaloids and have been the subjects of intensive phytochemical investigations. In Southeast Asia, Ancistrocladus tectorius, previously regarded as the only species of the genus from this region, is extremely polymorphic with respect to naphthylisoquinoline alkaloids, indicating that this taxon might be comprised of several morphologically similar species. We performed a comparative study of the ITS region of nuclear rDNA and of the trnK intron of cpDNA as well as an ISSR fingerprint analysis. Using 75 samples of A. tectorius from 21 locations in comparison to samples of other Ancistrocladus species from Asia and from West and Central Africa, we investigated patterns of species differentiation within this taxon. We found the high variability of chemical compounds described for A. tectorius to be paralleled by a high genetic variability of the units that have been assigned to this taxon. Samples assigned to A. tectorius were paraphyletic with respect to species from the Indian subcontinent, and intraspecific variability was comparable to interspecific variability among the African taxa. In addition, groups of individuals occurring in sympatry were found to be more similar to those from other locations, suggesting low levels of gene flow between those sympatric groups. This indicates either a considerable number of hybridization events during the evolution of A. tectorius or the existence of several distinguishable species not yet recognized. Our results are a first step in the development of species or population-specific markers for the prediction of the alkaloid spectrum of samples. This will help to improve the reproducibility of phytochemical research on Ancistrocladus.

SYNTHESIS: The role of adaptive trans-generational plasticity in biological invasions of plants

High‐impact biological invasions often involve establishment and spread in disturbed, high‐resource patches followed by establishment and spread in biotically or abiotically stressful areas. Evolutionary change may be required for the second phase of invasion (establishment and spread in stressful areas) to occur. When species have low genetic diversity and short selection history, within‐generation phenotypic plasticity is often cited as the mechanism through which spread across multiple habitat types can occur. We show that trans‐generational plasticity (TGP) can result in pre‐adapted progeny that exhibit traits associated with increased fitness both in high‐resource patches and in stressful conditions. In the invasive sedge, Cyperus esculentus, maternal plants growing in nutrient‐poor patches can place disproportional number of propagules into nutrient‐rich patches. Using the invasive annual grass, Aegilops triuncialis, we show that maternal response to soil conditions can confer greater stress tolerance in seedlings in the form of greater photosynthetic efficiency. We also show TGP for a phenological shift in a low resource environment that results in greater stress tolerance in progeny. These lines of evidence suggest that the maternal environment can have profound effects on offspring success and that TGP may play a significant role in some plant invasions.

Ancistrocladus benomensis (Ancistrocladaceae): a new species from Peninsular Malaysia

Ancistrocladus benomensis Rischer & G. Bringmann, a new species from Gunung Benom, Malaysia is described and illustrated. Diagnostic notes concerning morphology, occurrence of specific naphthylisoquinoline alkaloids, and support from molecular analyses are provided.