The evolution of angiosperm seed proteins: A methionine-rich legumin subfamily present in lower angiosperm Clades

Analysis of legumin-encoding cDNAs fromDioscorea caucasica Lipsky (Dioscoreaceae) and fromAsarum europaeum L. (Aristolochiaceae) shows that there is an especially methionine-rich legumin subfamily present in the lower angiosperm clades including the Monocotyledoneae. It is characterized by a methionine content of 3–4 mol% which is roughly triple the methionine proportion of most other legumins. These “MetR” legumins, if present, still have to be detected in the higher angiosperms including the important seed crops. Evolutionary analysis suggests that the MetR legumins are the result of a gene duplication allowing the differentiation of legumin genes according to their sulfur content. The duplication event must have taken place before the split into mono- and dicotyledonous plants but probably after the separation of angiosperms and gymnosperms. Correspondence to: H. Fischer     

Hypothesis for the evolution of three-helix Chl a/b and Chl a/c light-harvesting antenna proteins from two-helix and four-helix ancestors

The nuclear-encoded Chl a/b and Chl a/c antenna proteins of photosynthetic eukaryotes are part of an extended family of proteins that also includes the early light-induced proteins (ELIPs) and the 22 kDa intrinsic protein of PS II (encoded by psbS gene). All members of this family have three transmembrane helices except for the psbS protein, which has four. The amino acid sequences of these proteins are compared and related to the three-dimensional structure of pea LHC II Type I (Kühlbrandt and Wang, Nature 350: 130–134, 1991). The similarity of psbS to the three-helix members of the family suggests that the latter arose from a four-helix ancestor that lost its C-terminal helix by deletion. Strong internal similarity between the two halves of the psbS protein suggests that it in turn arose as the result of the duplication of a gene encoding a two-helix protein. Since psbS is reported to be present in at least one cyanobacterium, the ancestral four-helix protein may have been present prior to the endosymbiotic event or events that gave rise to the photosynthetic eukaryotes. The Chl a/b and Chl a/c antenna proteins, and the immunologically-related proteins in the rhodophytes may have had a common ancestor which was present in the early photosynthetic eukaryotes, and predated their division into rhodophyte, chromophyte and chlorophyte lineages. The LHC I-LHC II divergence probably occurred before the separation of higher plants from chlorophyte algae and euglenophytes, and the different Types of LHC I and LHC II proteins arose prior to the separation of angiosperms and gymnosperms.Abbreviations CAB Chl a/b-binding - ELIP early light-induced protein - FCP fucoxanthin-Chl a/c protein - PCR polymerase chain reaction - TMH trans-membrane helix     

The origin of Lotus corniculatus

Summary Earlier students of the origin of Lotus corniculatus suggested that this tetraploid species arose as an autotetraploid of the closely related diploid species L. tenuis or L. alpinus. More recent studies suggested that L. alpinus and L. japonicus could be ancestral forms. The present study of tannin content, phenolic content, cyanide production, morphology, cytogenetics, Rhizobium specificity and self-incompatibility in the corniculatus group virtually excludes the possibility that L. corniculatus could have arisen through autopolyploidy of L. tenuis or L. alpinus, and suggests that L. corniculatus arose through hybridization of L. alpinus and/or L. tenuis (probably as female parent) with L. uliginosus (probably as male parent), followed by chromosome doubling in the hybrid.     

Increased chemical resistance explains low herbivore colonization of introduced seaweed

The success of introduced species is often attributed to release from co-evolved enemies in the new range and a subsequent decreased allocation to defense (EICA), but these hypotheses have rarely been evaluated for systems with low host-specificity of enemies. Here, we compare herbivore utilization of the brown seaweed, Fucus evanescens, and its coexisting competitors both in its native and new ranges, to test certain predictions derived from these hypotheses in a system dominated by generalist herbivores. While F. evanescens was shown to be a preferred host in its native range, invading populations supported a less diverse herbivore fauna and it was less preferred in laboratory choice experiments with important herbivores, when compared to co-occurring seaweeds. These results are consistent with the enemy release hypothesis, despite the fact that the herbivore communities in both regions were mainly composed of generalist species. However, in contrast to the prediction of EICA, analysis of anti-grazing compounds indicated a higher allocation to defense in introduced compared to native F. evanescens. The results suggest that the invader is subjected to less intense enemy control in the new range, but that this is due to an increased allocation to defense rather than release from specialized herbivores. This indicates that increased resistance to herbivory might be an important strategy for invasion success in systems dominated by generalist herbivores.     

Spider cocoons and their suspension systems as barriers to generalist and specialist predators

Summary This study tests hypotheses regarding spider cocoons and their suspension systems as barriers to generalist and specialist predators. Evidence presented here suggests that the suspension systems ofMecynogea lemniscata andArgiope aurantia cocoons are effective barriers against small generalists such as ants, but fail to stop large generalists such as birds. Cocoon covers were found to be generally ineffective against generalist predators. Various component layers of these cocoons are shown, however, to be an effective barrier against the attack modes of specific predator guilds. Cocoon covers function primarily as barriers to specialists that use active “burrowing” larvae to gain entrance into the cocoon, while the flocculent silk layer is shown to be an effective barrier against specialists which use a long ovipositor to attack cocoons. These findings support suggestions that the primary role of the cocoon is to provide protection from predators and parasites. These results also support a close evolutionary relationship between cocoon architecture and specialized predators.     

Embryology and relationships ofGyrocarpus andHernandia (Hernandiaceae)

Two representative genera of Hernandiaceae,Gyrocarpus andHernandia, were investigated embryologically to contribute to a better understanding of their respective evolutionary position. Comparisons with other lauralean families using Chloranthaceae or Annonaceae (as a representative of Magnoliales) as an outgroup of Laurales (if present, plus other related taxa) support a lauraceous affinity for the two genera because of the presence of ramified raphal vascular bundles at the chalaza (a synapomorphy), but do not provide evidence for the separation of Hernandiaceae from Lauraceae.Hernandia rather shares with Lauraceae two apomorphies (i.e., the seed pachychalazy and the ruminate seed) which may be homoplasies judged from results of cladistic and molecular studies published elsewhere.Hernandia is greatly divergent from an ancestral line common withGyrocarpus and is even diversified within the genus. Based on evidence from embryology as well as from other sources, it seems best to accept two separate subfamilies in Hernandiaceae as usually have been accepted: one is a derived subfamily Hernandioideae, and the other a less specialized Gyrocarpoideae.     

Generic delimitation and phylogeny of theCarduncellus-Carthamus complex (Asteraceae) based on ITS sequences

Within the Mediterranean complexCarduncellus-Carthamus, taxonomic classification has proven problematic. Numerous attempts to clarify the relative systematic boundaries have included splittingCarduncellus andCarthamus into several genera, but none of these proposed classifications have been generally accepted. For a comprehensive resolution of the relationships within this group, we used sequences of the Internal Transcribed Spacers (ITS) of nuclear ribosomal DNA. The results indicate that the complex should be classified into four genera:Carduncellus, Carthamus, Femeniasia andPhonus. The relationship between the western group (Carduncellus, Femeniasia andPhonus) and the eastern genusCarthamus are not resolved by analysis of ITS sequences, but the two groups are probably not close relatives. The ITS classifications corresponded with biogeography and less with morphological characters, which have also been the main source of confusion in traditional classifications. Most of the unusual morphological features in theCarduncellus-Carthamus complex appear to be reversals to ancestral character states.     

Reconstructing the history of Campanulaceae with a Bayesian approach to molecular dating and dispersal–vicariance analyses

We reconstruct here the spatial and temporal evolution of the Campanula alliance in order to better understand its evolutionary history. To increase phylogenetic resolution among major groups (Wahlenbergieae–Campanuleae), new sequences from the rbcL region were added to the trnL-F dataset obtained in a previous study. These phylogenies were used to infer ancestral areas and divergence times in Campanula and related genera using a Bayesian approach to molecular dating and dispersal–vicariance analyses that takes into account phylogenetic uncertainty. The new phylogenetic analysis confirms Platycodoneae as the sister group of Wahlenbergieae–Campanuleae, the two last ones inter-graded into a well-supported clade. Biogeographic and dating analyses suggest that Western Asia and the Eastern Mediterranean have played a major role as centers of migration and diversification within the Campanula alliance, probably in relation to the intense orogenic activity that took place in this region during the Late Neogene, and that could have promoted isolation and allopatric speciation within lineages. Diversification rates within several Campanula lineages would have increased at the end of the Miocene, coinciding with the Messinian Stage. Strong selective pressures from climate changes and the expansion of mountainous regions during this period are suggested to explain the adaptation to drought, cold or disturbed environments observed in many Campanula species. Several independent long-distance dispersal events to North America are inferred within the Rapunculus clade, which seem to be related to high ploidy levels.     

Effect of larval host food substrate on egg load dynamics, egg size and adult female size in four species of braconid fruit fly (Diptera: Tephritidae) parasitoids

Life history theory predicts that individuals will allocate resources to different traits so as to maximize overall fitness. Because conditions experienced during early development can have strong downstream effects on adult phenotype and fitness, we investigated how four species of synovigenic, larval-pupal parasitoids that vary sharply in their degree of specialization (niche breadth) and life history (Diachasmimorpha longicaudata, Doryctobracon crawfordi, Opius hirtus and Utetes anastrephae), allocate resources acquired during the larval stage towards adult reproduction. Parasitoid larvae developed in a single host species reared on four different substrates that differed in quality. We measured parasitoid egg load at the moment of emergence and at 24 h, egg numbers over time, egg size, and also adult size. We predicted that across species the most specialized would have a lower capacity to respond to changes in host substrate quality than wasps with a broad host range, and that within species, females that emerged from hosts that developed in better quality substrates would have the most resources to invest in reproduction. Consistent with our predictions, the more specialized parasitoids were less plastic in some responses to host diet than the more generalist. However, patterns of egg load and size were variable across species. In general, there was a remarkable degree of reproductive effort-allocation constancy within parasitoid species. This may reflect more “time-limited” rather than “egg-limited” foraging strategies where the most expensive component of reproductive success is to locate and handle patchily-distributed and fruit-sequestered hosts. If so, egg costs, independent of degree of specialization, are relatively trivial and sufficient resources are available in fly larvae stemming from all of the substrates tested.     

Taxonomic studies ofAsarum sensu lato

The floral vascular anatomy of 12 species representing each ofAsarum s. str.,Asiasarum, Geotaenium, Heterotropa andHexastylis are compared to clarify intergeneric relationships. The five genera have basically similar structures in floral morphology and vasculature, and consistently have a six-carpelled compound ovary and the associated similar placental vasculature. They show, however, a significant difference in the position and the constituent of the “ventral” carpellary bundles in the placental axis betweenAsiasarum-Heterotropa-Hexastylis andAsarum-Geotaenium. InAsiasarum, Heterotropa andHexastylis the ventral bundles of each carpel are basically free and antilocular as expected in the least specialized compound ovary of angiosperms; in contrast, inAsarum andGeotaenium the ventral carpellary bundles are antiseptal and heterogenous (i.e., formed by the lateral fusion of ventral bundles of adjacent carpels). Shared probable apomorphic floral vasculature, as well as shared single style-column, suggests the closest mutual relationships betweenAsarum andGeotaenium. In terms of floral morphology and anatomy,Asiasarum, Heterotropa andHexastylis retain plesiomorphies. Possible chromosomal evolution in the related genera is also discussed.     

Male Gametic Cell-specific Histone <Emphasis Type="Italic">gH2A</Emphasis> Gene of <Emphasis Type="Italic">Lilium longiflorum</Emphasis>: Genomic Structure and Promoter Activity in the Generative Cell

A genomic clone containing the gH2A gene, a histone variant specifically expressed in male gametic cells within the pollen of Lilium longiflorum, was isolated. Sequence analysis revealed that the coding region of the gene is interrupted by one intron, as is the case with the somatic type of plant histone H2A genes, suggesting derivation from the same ancestral gene containing one intron. In addition, a 2.8-kbp fragment of the 5′ upstream region of gH2A contained TATA and CAAT boxes, but neither a plant histone-specific regulatory DNA element nor vegetative cell-specific cis-elements were found. A histochemical study of stable transformants demonstrated that the 5′ upstream region of the gene can drive gene expression specifically in the generative cell of pollen; no activity was detectable in the vegetative cell or in other reproductive and vegetative tissues of transgenic Nicotiana tabacum. These results strongly suggest that the generative cell can direct specific gene expression, that this expression may be regulated by a putative male gametic factor, and that the gH2A promoter may therefore serve as a useful male gametic cell fate marker in angiosperms.     

Phylogeny of the avian genus Pitohui and the evolution of toxicity in birds

Bird species in the avian genus Pitohui contain potent neurotoxic alkaloids that may be used for defense. The genus comprises multiple species that are endemic to New Guinea and were presumed to belong to the family Pachycephalidae or Colluricinclidae, within the core corvoidea, an ancient Australasian radiation of crow-like birds. In order to understand the evolution of toxicity within the genus Pitohui, we sequenced three mitochondrial and two nuclear gene segments and reconstructed a phylogeny of the genus Pitohui and its putative relatives. We show that the genus Pitohui is polyphyletic, and consists of five different lineages. Using Bayesian ancestral state reconstruction, we estimate that toxicity likely evolved multiple times within this group. Furthermore, because the morphological and behavioral similarity among these poisonous birds appears to have evolved convergently, we hypothesize that this may be a possible example of Müllerian mimicry in birds. The Morningbird of Palau, Micronesia, that has often been included in the genus Pitohui, actually belongs in the genus Pachycephala and offers an intriguing case of pronounced evolution on a remote oceanic island.     

Summer food of sympatric red fox and pine marten in the German Alps

Based on fecal analyses, we compared summer diet composition and trophic niche breadth for the sympatric red fox Vulpes vulpes (n=55 scats) and pine marten Martes martes (n=64) in the foothills of the German Alps. Mammals accounted for 41 and 51% of the consumed biomass by pine martens and red foxes, respectively, and no single mammal species exceeded 8% of the diet. The larger red fox consumed a wider range of prey sizes than the smaller pine marten, and both consumed large amounts of plants and also insects. Whereas the Levins index suggested that both predators have specialist feeding niches, the Shannon-Wiener index showed that both predators were relatively generalist. Despite its preliminary nature, our study suggests that a strict distinction between generalist and specialist trophic niches is not justified for medium-sized carnivores in the Alps, particularly as results greatly depend on the indices used.     

Hypoxia tolerance and air-breathing ability correlate with habitat preference in coral-dwelling fishes

Hypoxia tolerance and air-breathing occur in a range of freshwater, estuarine and intertidal fishes. Here it is shown for the first time that coral reef fishes from the genera Gobiodon, Paragobiodon and Caracanthus, which all have an obligate association with living coral, also exhibit hypoxia tolerance and a well-developed air-breathing capacity. All nine species maintained adequate respiration in water at oxygen concentrations down to 15–25% air saturation. This hypoxia tolerance is probably needed when the oxygen levels in the coral habitat drops sharply at night. Air-breathing abilities of the species correlated with habitat association, being greatest (equaling oxygen uptake in water) in species that occupy corals extending into shallow water, where they may become air exposed during extreme low tides. Air-breathing was less well-developed or absent in species inhabiting corals from deeper waters. Loss of scales and a network of subcutaneous capillaries appear to be key adaptations allowing cutaneous respiration in air. While hypoxia tolerance may be an ancestral trait in these fishes, air-breathing is likely to be a more recent adaptation exemplifying convergent evolution in the unrelated genera Gobiodon and Caracanthus in response to coral-dwelling lifestyles.     

Generalized plant defense: effects on multiple species

Summary Two species of lepidopteran herbivores, Manduca sexta (Sphingidae) and Trichoplusia ni (Noctuidae), were reared on synthetic diet containing either the alkaloid nicotine or the flavonoid rutin. Survival and pupal weight of the specialist M. sexta did not differ when larvae were reared on diet containing nicotine or rutin. In contrast, the generalist T. ni did not survive on diet containing 0.125% nicotine or greater, whereas larvae survived on all concentrations of rutin. These data demonstrate that the alkaloid nicotine is inhibitory toward generalist, but not specialist herbivores, whereas the flavonoid rutin has no effect on specialist herbivores and limited effects on generalist herbivores. Five species of Pseudomonas bacterial pathogens: P. syringae, P. syringae pv. angulata, P. syringae pv. tabaci, P. fluorescens, and P. solanacearum were grown on nutrient agar containing nicotine or rutin at concentrations ranging from 0.0 to 1.0% wet weight in 0.1% intervals. No species of Pseudomonas grew at concentrations greater than 0.5% nicotine when 10⁶ colony forming units (cfu) were used, but growth occurred at all concentrations of rutin when 10² cfu were used. These data indicate that nicotine was inhibitory to growth of both herbivores and pathogens, suggesting that certain plant secondary chemicals with high toxicity are of a generalized nature and affect multiple species. Differences in the sensitivity of organisms to allelochemicals such as generalist or specialist can make it appear that specific allelochemicals affect specific organisms, when in fact it is the tolerance of the organism to the plant chemical that is responsible. In four separate studies, the growth of M. sexta, T. ni and Helicoverpa zea was significantly lower on plants inoculated with P. solanacearum. Alteration in leaf quality by P. solanacearum was due to either reductions in leaf nutrients or increases in allelochemicals. We speculate that localized or systemic induction by both herbivores and pathogens can cause changes in leaf quality, effecting each other's subsequent colonization. The generalized nature of plant secondary compounds and potential reciprocal effects on induction by both species suggests that herbivores and pathogens may affect plant quality through induction and diffuse interactions of disparate species can alter the community of organisms colonizing a plant.     

Identification of two differentially regulated isoforms of protochlorophyllide oxidoreductase (POR) from tobacco revealed a wide variety of light- and development-dependent regulations of POR gene expression among angiosperms

NADPH-protochlorophyllide oxidoreductase (POR) catalyzes the light-dependent reduction of protochlorophyllide a in the chlorophyll biosynthetic pathway. Here, we identified two distinct POR cDNAs from tobacco. Both POR isoforms are encoded by a respective single copy gene in tobacco genome. The overall deduced amino acid sequences of two tobacco cDNAs, designated here POR1 and POR2, displayed significant identities (∼75%), but showed different patterns of light and developmental regulation. In contrast to the previously isolated POR isoforms of Arabidopsis thaliana and barley, the expression of both tobacco POR isoforms were not negatively regulated by light and persisted in matured green tissues. Furthermore, the expression of both genes appeared to be regulated by a diurnal regulation. These results show a wide variety of light- and development-dependent regulations of POR gene expression among angiosperms. Furthermore, phylogenetic analysis including tobacco revealed that POR gene family is differentially represented by angiosperms, most of which is probably caused by independent gene duplication in individual plant. Present results imply a modification of the previous concept that chlorophyll biosynthesis and chloroplast differentiation in angiosperms are ubiquitously controlled by unique functions of two POR isoforms. This revised version was published online in June 2006 with corrections to the Cover Date.     

Microhabitat use,seasonal activity and diet of the snake-eyed skink (<Emphasis Type="Italic">Ablepharus kitaibelii fitzingeri</Emphasis>) in comparison with sympatric lacertids in Hungary

Microhabitat selection and seasonal activity of the snake-eyed skink, Ablephaus kitaibelii fitzingeri, are compared to the two lacertid lizards (Lacerta viridis and Podarcis muralis) that co-occur in many of its habitats. The food composition of A. k. fitzingeri is also described. Significant differences in microhabitat selection and seasonal activity among the three species were found. The snake-eyed skink was associated with open grasslands, and with a low level of scrub, bare soil and rock cover. The microhabitat preference of L. viridis was quite similar to that of the skink, but with a higher preference for scrub. P. muralis occurred in places with greater rock and bare soil cover, and more scrub than A. k. fitzingeri. Activity of the snake-eyed skink decreased dramatically in summer, probably because of the reduced thermal inertia originating from the extremely small size of this species, but its seasonal activity overlapped with those of the lacertids. Stomach content analysis of the snake-eyed skink suggests that it is a generalist predator of small, mainly flightless arthropod prey. Competition with juvenile lacertids and predation by adult L. viridis are conceivable for the snake-eyed skink.     

A comparison of tapetal structure and function in pteridophytes and angiosperms

This article is based on a survey of literature with particular reference to the structure and functioning of the tapetum during sporogenesis in angiosperms and pteridophytes. Some original observations onSchizaea pectinata andSelaginella japonica are also included. In the past, superficial similarities in the structure and function of pollen grains and spores have dominated the research approach, but patterns of development and the functioning of the tapetum during sporogenesis in angiosperms and pteridophytes are shown to differ quite significantly and raises questions relating to homologies. It is suggested that direct comparisons may no longer be appropriate.     

Entwicklungsgeschichte und Ultrastruktur von Pollenkitt und Exine bei nahe verwandten entomophilen und anemophilen Angiospermensippen:Ranunculaceae,Hamamelidaceae, Platanaceae undFagaceae

Transfer of fresh pollen either by wind or by insects is strongly related to the degree of its stickiness. The sticky substances involved should be understood as pollenkitt. Ultrastructural investigations indicate that the sticky pollen of entomophilous angiosperms (in this publicationHamamelis vernalis andH. virginiana, Corylopsis platypetala) results from the deposition of usually electron-dense, homogeneous pollenkitt mainly on the outside layer of the exine. In contrast, the pollen of anemophilous angiosperms (in this publicationParrotia persica, Platanus orientalis, Thalictrum flavum andQuercus robur), but also of some entomophilous angiosperms with special pollination ecology (e.g.Aquilegia vulgaris) is rather dry and powdery. In these cases the pollenkitt often is electron-transparent and inhomogeneous and is mainly removed into the cavities of the exine. Ultrastructure and deposition of pollen and pollenkitt in ambophilous angiosperms (in this publicationThalictrum minus, Castanea sativa) are ± intermediate.

     

Guanylyl cyclases in unicellular organisms

Guanylyl cyclases in eukaryotic unicells were biochemically investigated in the ciliates Paramecium and Tetrahymena, in the malaria parasite Plasmodium and in the ameboid Dictyostelium. In ciliates guanylyl cyclase activity is calcium-regulated suggesting a structural kinship to similarly regulated membrane-bound guanylyl cyclases in vertebrates. Yet, cloning of ciliate guanylyl cyclases revealed a novel combination of known modular building blocks. Two cyclase homology domains are inversely arranged in a topology of mammalian adenylyl cyclases, containing two cassettes of six transmembrane spans. In addition the protozoan guanylyl cyclases contain an N-terminal P-type ATPase-like domain. Sequence comparisons indicate a compromised ATPase function. The adopted novel function remains enigmatic to date. The topology of the guanylyl cyclase domain in all protozoans investigated is identical. A recently identified Dictyostelium guanylyl cyclase lacks the N-terminal P-type ATPase domain. The close functional relation of Paramecium guanylyl cyclases to mammalian adenylyl cyclases has been established by heterologous expression, respective point mutations and a series of active mammalian adenylyl cyclase/Paramecium guanylyl cyclase chimeras. The unique structure of protozoan guanylyl cyclases suggests that unexpectedly they do not share a common guanylyl cyclase ancestor with their vertebrate congeners but probably originated from an ancestral mammalian-type adenylyl cyclase.