Maxim S. Nuraliev

Exploring the limits for reduction of plastid genomes: a case study of the mycoheterotrophic orchids Epipogium aphyllum and Epipogium roseum.

The question on the patterns and limits of reduction of plastid genomes in nonphotosynthetic plants and the reasons of their conservation is one of the intriguing topics in plant genome evolution. Here, we report sequencing and analysis of plastid genome in nonphotosynthetic orchids Epipogium aphyllum and Epipogium roseum, which, with sizes of 31 and 19 kbp, respectively, represent the smallest plastid genomes characterized by now. Besides drastic reduction, which is expected, we found several unusual features of these “minimal” plastomes: Multiple rearrangements, highly biased nucleotide composition, and unprecedentedly high substitution rate. Only 27 and 29 genes remained intact in the plastomes of E. aphyllum and E. roseum—those encoding ribosomal components, transfer RNAs, and three additional housekeeping genes (infA, clpP, and accD). We found no signs of relaxed selection acting on these genes. We hypothesize that the main reason for retention of plastid genomes in Epipogium is the necessity to translate messenger RNAs (mRNAs) of accD and/or clpP proteins which are essential for cell metabolism. However, these genes are absent in plastomes of several plant species; their absence is compensated by the presence of a functional copy arisen by gene transfer from plastid to the nuclear genome. This suggests that there is no single set of plastid-encoded essential genes, but rather different sets for different species and that the retention of a gene in the plastome depends on the interaction between the nucleus and plastids.

The Plastid Genome of Mycoheterotrophic Monocot Petrosavia stellaris Exhibits Both Gene Losses and Multiple Rearrangements

Plastid genomes of nonphotosynthetic plants represent a perfect model for studying evolution under relaxed selection pressure. However, the information on their sequences is still limited. We sequenced and assembled plastid genome of Petrosavia stellaris, a rare mycoheterotrophic monocot plant. After orchids, Petrosavia represents only the second family of nonphotosynthetic monocots to have its plastid genome examined. Several unusual features were found: retention of the ATP synthase genes and rbcL gene; extensive gene order rearrangement despite a relative lack of repeat sequences; an unusually short inverted repeat region that excludes most of the rDNA operon; and a lack of evidence for accelerated sequence evolution. Plastome of photosynthetic relative of P. stellaris, Japonolirion osense, has standard gene order and does not have the predisposition to inversions. Thus, the rearrangements in the P. stellaris plastome are the most likely associated with transition to heterotrophic way of life.

Flower structure and development in Tupidanthus calyptratus (Araliaceae): an extreme case of polymery among asterids

Flowers of Tupidanthus show an extreme case of floral polymery among asterids. Floral development and gynoecium structure have been examined. The floral meristem has a complex folded shape. The tiny calyx is initiated as a continuous ring primordium. The corolla is initiated as a lobed ring and develops into a calyptra. All stamen primordia appear simultaneously as a single whorl. The carpels, also in a single whorl, tend to alternate with the stamens. Some Schefflera species related to Tupidanthus are also studied. The flower of Tupidanthus is interpreted as a result of fasciation. Further investigation should determine whether mutation(s) in gene(s) of the CLAVATA family are responsible for the fasciation here. The significance of Tupidanthus for understanding spatial pattern formation in flowers of Araliaceae, and both functional and developmental constraints in angiosperm flowers with a single polymerous carpel whorl are discussed.

Floral Anatomy of Asian Schefflera (Araliaceae, Apiales): Comparing Variation of Flower Groundplan and Vascular Patterns

Floral morphology and vascular anatomy in members of the Asian Schefflera clade (Araliaceae) are studied. This clade is of special interest because of secondary loss of flower groundplan stability and increase of merism. Among five species studied, three have isomerous pentamerous flowers, one has (almost) isomerous polymerous flowers, and one has nonisomerous flowers as a result of increased carpel number. Loss of calyx innervation and reduction of sepals are suggested as apomorphic for the subclade Heptapleurum s.l. Tupidanthus calyptratus, a member of this subclade with the most polymerous gynoecium among asterids, shares those features, too. Range of petal venation diversity within the species examined exceeds what was previously estimated for the family Araliaceae and the order Apiales. Formation of anastomoses between the bundles of petals and stamens in bisexual flowers of Schefflera venulosa is suggested as an effect of high auxin production in developing anthers. A shift of the ovule supply from ventral bundles to lateral ones occurs in different lineages of Apiales. Fusion between peripheral and dorsal bundles is an effect of flower topography that may not be considered an advanced character state. Strong differences in floral vasculature between closely related species with the same flower groundplan are highlighted.

Aspidistra cylindrica (Asparagaceae), a New Species from Southern Vietnam

Abstract Aspidistra cylindrica, a new species from southern Vietnam (Kon Tum province), is described and illustrated. The new species possesses a unique combination of cylindrical shape of pistil and shoot system with foliage leaves crowded in groups and not divided into petiole and lamina. Aspidistra cylindrica resembles A. muricata but differs in longer leaves, shorter and wider perigone, shorter pistil, shape and colour of perigone lobes, anther position, and stigma shape. The conservation status of A. cylindrica is assessed. A key for species of Aspidistra in southern Vietnam is provided.

Gradual vs. abrupt reduction of carpels in syncarpous gynoecia: A case study from Polyscias subg. Arthrophyllum (Araliaceae: Apiales)

PREMISE OF THE STUDY Revealing the relative roles of gradual and abrupt transformations of morphological characters is an important topic of evolutionary biology. Gynoecia apparently consisting of one carpel have evolved from pluricarpellate syncarpous gynoecia in several angiosperm clades. The process of reduction can involve intermediate stages, with one fertile and one or more sterile carpels (pseudomonomery). The possible origin of monomery directly via an abrupt change of gynoecium merism has been a matter of dispute. We explore the nature of gynoecium reduction in a clade of Araliaceae. METHODS The anatomy and development of unilocular gynoecia are investigated using light and scanning electron microscopy in two members of Polyscias subg. Arthrophyllum. Gynoecium diversity in the genus is discussed in a phylogenetic framework. KEY RESULTS Unilocular gynoecia with one fertile ovule have evolved at least four times in Polyscias, including one newly discovered case. The two unilocular taxa investigated are unicarpellate, without any traces of reduced sterile carpels. Carpel orientation is unstable, and the ovary roof and style contain numerous vascular bundles without clearly recognizable dorsals or ventrals. In contrast to pluricarpellate Araliaceae and Apiaceae, the cross zone is apparently oblique in the unicarpellate species. CONCLUSIONS No support was found for gradual gynoecium reduction via pseudomonomery. The abrupt origin of monomery via direct change of gynoecium merism and the unstable carpel orientation observed are related to the general lability of the flower groundplan in Polyscias. The apparent occurrence of the unusual oblique cross zone in unicarpellate Araliaceae can be explained by developmental constraints.

Genus Huberantha (Annonaceae) Revisited: Erection of Polyalthiopsis, a New Genus for H. floribunda, with a New Combination H. luensis

The identity of an enigmatic species Huberantha floribunda (Annonaceae) is reassessed using molecular phylogenetic analyses of up to seven combined plastid markers (matK, ndhF, rbcL, ycf1 exons; trnL intron; trnL-trnF, psbA-trnH intergenic spacers), constituting up to ca. 7 kbp. Huberantha floribunda does not fall into Huberantha clade, but is retrieved as the sister group of Miliusa with no support, necessitating the recognition of a new genus, to accommodate this species. Polyalthiopsis Chaowasku gen. nov. along with Huberantha and Miliusa form an unsupported to weakly supported clade within the tribe Miliuseae. Morphology of Polyalthiopsis is somewhat intermediate between morphologies of Huberantha and Miliusa. It primarily differs from Huberantha by often possessing unequal petal whorls and a seed raphe that is broadly grooved and partially slightly raised in the middle. Polyalthiopsis differs from Miliusa mainly by having a dilated truncate connective apex of the stamens and outer petals that are much larger than the sepals. In addition, Huberantha luensis (Pierre) Chaowasku, a new combination for Polyalthia luensis is made based on an integrative approach of morphological examination coupled with molecular phylogenetic inferences.

Gynoecium Evolution in Angiosperms: Monomery, Pseudomonomery, and Mixomery

The presence of a gynoecium composed of carpels is a key feature of angiosperms. The carpel is often regarded as a homologue of the gymnosperm megasporophyll (that is, an ovule-bearing leaf), but higher complexity of the morphological nature of carpel cannot be ruled out. Angiosperm carpels can fuse to form a syncarpous gynoecium. A syncarpous gynoecium usually includes a well-developed compitum, an area where the pollen tube transmitting tracts of individual carpels unite to enable the transition of pollen tubes from one carpel to another. This phenomenon is a precondition to the emergence of carpel dimorphism manifested as the absence of a functional stigma or fertile ovules in part of the carpels. Pseudomonomery, which is characterized by the presence of a fertile ovule (or ovules) in one carpel only, is a specific case of carpel dimorphism. A pseudomonomerous gynoecium usually has a single plane of symmetry and is likely to share certain features of the regulation of morphogenesis with the monosymmetric perianth and androecium. A genuine monomerous gynoecium consists of a single carpel. Syncarpous gynoecia can be abruptly transformed into monomerous gynoecia in the course of evolution or undergo sterilization and gradual reduction of some carpels. Partial or nearly complete loss of carpel individuality that precludes the assignment of an ovule (or ovules) to an individual carpel is observed in a specific group of gynoecia. We termed this phenomenon mixomery, since it should be distinguished from pseudomonomery.

Staminate flower of Prunus s. l. (Rosaceae) from Eocene Rovno amber (Ukraine)

The late Eocene ambers provide plethora of animal and plant fossils including well-preserved angiosperm flowers from the Baltic amber. The Rovno amber from NW Ukraine resembles in many aspects the Baltic amber; however, only fossilized animals and some bryophytes have yet been studied from the Rovno amber. We provide the first detailed description of an angiosperm flower from Rovno amber. The flower is staminate with conspicuous hypanthium, double pentamerous perianth and whorled androecium of 24 stamens much longer than the petals. Sepals are sparsely pubescent and petals are densely hirsute outside. The fossil shares important features with extant members of Prunus subgen. Padus s. l. (incl. Laurocerasus, Pygeum and Maddenia), especially with its evergreen paleotropical species. It is described here as a new species Prunus hirsutipetala D.D.Sokoloff, Remizowa et Nuraliev. Our study provides the first convincing record of fossil flowers of Rosaceae from Eocene of Europe and the earliest fossil flower of Prunus outside North America. Our record of a plant resembling extant tropical species supports palaeoentomological evidences for warm winters in northwestern Ukraine during the late Eocene, as well as suggesting a more significant role of tropical insects in Rovno amber than inferred from Baltic amber.

Jasminanthes tuyetanhiae (Apocynaceae, Asclepiadoideae), a New Species from Vietnam, and J. pilosa New for Vietnam

Jasminanthes tuyetanhiae T.B. Tran & Rodda (Apocynaceae, Asclepiadoideae) is described as a new species from Vietnam. It differs from the morphologically similar J. chunii by its shorter peduncles and by the triangular-ovate calyx lobes. Jasminanthes pilosa, earlier known from China and Thailand, is lectotypified and newly recorded for the flora of Vietnam, fully described and for the first time colour photographs are provided. An appendix with key characters for the separation of all seven Jasminanthes species as well as the key to the species of Jasminanthes are included.