Phylogenetic relationships in Rosaceae inferred from chloroplast matK and trnL-trnF nucleotide sequence data

 Phylogenetic relationships in Rosaceae were studied using parsimony analysis of nucleotide sequence data from two regions of the chloroplast genome, the matK gene and the trnL-trnF region. As in a previously published phylogeny of Rosaceae based upon rbcL sequences, monophyletic groups were resolved that correspond, with some modifications, to subfamilies Maloideae and Rosoideae, but Spiraeoideae were polyphyletic. Three main lineages appear to have diverged early in the evolution of the family: 1) Rosoideae sensu stricto, including taxa with a base chromosome number of 7 (occasionally 8); 2) actinorhizal Rosaceae, a group of taxa that engage in symbiotic nitrogen fixation; and 3) the rest of the family. The spiraeoid genus Gillenia, not included in the rbcL study, was strongly supported as the sister taxon to Maloideae sensu lato. A New World origin of Maloideae is suggested. The position of the economically important genus Prunus and the status of subfamily Amygdaloideae remain unresolved. Received February 27, 2001 Accepted October 11, 2001     

Phylogeny and classification of Rosaceae

Phylogenetic relationships among 88 genera of Rosaceae were investigated using nucleotide sequence data from six nuclear (18S, gbssi1, gbssi2, ITS, pgip, and ppo) and four chloroplast (matK, ndhF, rbcL, and trnL-trnF) regions, separately and in various combinations, with parsimony and likelihood-based Bayesian approaches. The results were used to examine evolution of non-molecular characters and to develop a new phylogenetically based infrafamilial classification. As in previous molecular phylogenetic analyses of the family, we found strong support for monophyly of groups corresponding closely to many previously recognized tribes and subfamilies, but no previous classification was entirely supported, and relationships among the strongly supported clades were weakly resolved and/or conflicted between some data sets. We recognize three subfamilies in Rosaceae: Rosoideae, including Filipendula, Rubus, Rosa, and three tribes; Dryadoideae, comprising the four actinorhizal genera; and Spiraeoideae, comprising Lyonothamnus and seven tribes. All genera previously assigned to Amygdaloideae and Maloideae are included in Spiraeoideae. Three supertribes, one in Rosoideae and two in Spiraeoideae, are recognized.     

The granule-bound starch synthase (GBSSI) gene in the Rosaceae: multiple loci and phylogenetic utility

We sampled the 5' end of the granule-bound starch synthase gene (GBSSI or waxy) in Rosaceae, sequencing 108 clones from 18 species in 14 genera representing all four subfamilies (Amygdaloideae, Maloideae, Rosoideae, and Spiraeoideae), as well as four clones from Rhamnus catharticus (Rhamnaceae). This is the first phylogenetic study to use the 5' portion of this nuclear gene. Parsimony and maximum-likelihood analyses of 941 bases from seven complete and two partial exons demonstrate the presence of two loci (GBSSI-1 and GBSSI-2) in the Rosaceae. Southern hybridization analyses with locus-specific probes confirm that all four Rosaceae subfamilies have at least two GBSSI loci, even though only one locus has been reported in all previously studied diploid flowering plants. Phylogenetic analyses also identify four clades representing four loci in the Maloideae. Phylogenetic relationships inferred from GBSSI sequences are largely compatible with those from chloroplast (cpDNA: ndhF, rbcL) and nuclear ribosomal internal transcribed spacer (nrITS) DNA. Large clades are marked by significant intron variation: a long first intron plus no sixth intron in Maloideae GBSSI-1, a long fourth intron in Rosoideae GBSSI-1, and a GT to GC mutation in the 5' splice site of the fourth intron in all GBSSI-2 sequences. Our data do not support the long-held hypothesis that Maloideae originated from an ancient hybridization between amygdaloid and spiraeoid ancestors. Instead, Spiraeoideae genera (Kageneckia and Vauquelinia) are their closest relatives in all four GBSSI clades.     

NUCLEAR DNA CONTENT VARIATION WITHIN THE ROSACEAE

Nuclear DNA content has been estimated using flow cytometry for 17 species and eight cultivars of Malus and for 44 species of 29 other genera within the Rosaceae. Compared to other angiosperms, diploid genome sizes vary little within the family Rosaceae and within the genus Malus. C-values of genera within the subfamilies Spiraeoideae and Rosoideae are among the smallest of flowering plants thus far reported. In general, the Maloideae have the largest diploid genomes of the family, consistent with their higher chromosome numbers and presumed polyploid origin.     

Phylogenetic relationships in Maloideae (Rosaceae): evidence from sequences of the internal transcribed spacers of nuclear ribosomal DNA and its congruence with morphology

We used sequences from both internal transcribed spacers (ITS) and a small portion of the 5.8S gene of nuclear ribosomal DNA (nrDNA) for phylogenetic reconstruction of 19 genera of Maloideae and four potential outgroups from the Rosaceae. Parsimony analyses indicate that Maloideae are not monophyletic; Vauquelinia, which is traditionally placed in Spiraeoideae, and two genera of the Maloideae, Eriobotrya and Rhaphiolepis, form a well-supported clade that is the sister to the remainder of the subfamily. Although our ITS phylogenetic hypothesis is highly resolved, there is considerable homoplasy, and support, as indicated by bootstrap values and decay indices, is relatively weak for all groups except four: Eriobotrya-Rhaphiolepis-Vauquelinia, Crataegus-Mespilus, Amelanchier-Peraphyllum-Malacomeles, and Cydonia-Pseudocydonia. Our DNA sequence data do not support a broad interpretation of Sorbus. Intergeneric hybridization, which is prevalent in Maloideae, occurs between genera that are far removed from one another on our most-parsimonious trees. We infer an overall phylogeny from separate analyses of ITS DNA sequences and recently published morphological and wood anatomical studies of Maloideae and from analyses after pooling these data sets. The four most strongly supported clades of the ITS phylogeny appear in the phylogeny based on pooled data.     

Distribution of sorbitol in rosaceae

77 leaf samples representing 68 taxa of Rosaceae were investigated for the presence of sorbitol. A procedure for the quantitative estimation of sorbitol in dry plant tissues was elaborated; it made use of extraction by percolation and capillary GLC analysis of the silylated extracts. All Maloideae and Prunoideae and most Spiraeoideae were found to accumulate sorbitol. The subfamily Rosoideae was found to be heterogeneous in this respect; in most tribes sorbitol is totally lacking, but in Kerrieae, Adenostomeae and part of Dryadeae sorbitol is present in variable amounts. A clear-cut correlation between sorbitol accumulation and basic chromosome number seems to exist in Rosaceae.     

Parasite relationships and disposition of Filipendula

Filipendula spp. are attacked by rust fungi on the genusTriphragmium. Several related genera (tribe Phragmidieae) occur wholly or partly on Rosaceae, and all are restricted to genera in Rosoideae. It appears, by inference, thatFilipendula also belongs to this subfamily. The only recorded rusts of Spiraeoideae are distantly related, and appear, from morphology and total host relationship, to be of much earlier origin.     

Floral morphology of Maloideae (Rosaceae) and its systematic relevance

Flowers of 169 species of Rosaceae subfamily Maloideae, which were chosen to represent the taxonomic and geographic diversity of the group, were studied to ascertain their morphological variation and its systematic relevance. We describe and illustrate variation in size, indumentum, color, and macroscopic structural features. Most maloid species have syncarpous flowers with two to five carpels in which the ovary is at least three-quarters inferior, whereas species of other Rosaceae subfamilies have apocarpous or unicarpellate flowers with superior ovaries. However, maloid flowers show significant variation in the degree of carpel connation and of ovary adnation to the hypanthium. Cotoneaster, Heteromeles, and Pyracantha are completely apocarpous, and Dichotomanthes is perigynous with a completely superior ovary. Thus, no one floral character is sufficient to separate the Maloideae from other subfamilies of Rosaceae. Differences among their flowers support our recognition of Malus, Pyrus, and Sorbus as separate genera. Further, we argue for removal of Docyniopsis and Eriolobus from Malus, division of Sorbus into several genera, and union of Aronia, Photinia, and Stranvaesia. No floral characters support the traditional dichotomy of the subfamily into tribes Crataegeae and Sorbeae.     

Development and bin mapping of strawberry genic-SSRs in diploid <Emphasis Type="Italic">Fragaria</Emphasis> and their transferability across the Rosoideae subfamily

Cultivated strawberry (Fragaria × ananassa) together with other economically important genera such as Rosa (roses) and Rubus (raspberry and blackberry) belongs to the subfamily Rosoideae. There is increasing interest in the development of transferable markers to allow genome comparisons within the Rosaceae family. In this report, 122 new genic microsatellite (SSR) markers have been developed from cultivated strawberry and its diploid ancestor Fragaria vesca. More than 77% of the sequences from which the markers were developed show significant homology to known or predicted proteins and more than 92% were polymorphic among strawberry cultivars, representing valuable markers in transcribed regions of the genome. Sixty-three SSRs were polymorphic in the diploid Fragaria reference population and were bin-mapped together with another five previously reported but unmapped markers. In total, 72 loci were distributed across the seven linkage groups. In addition, the transferability of 174 Fragaria SSRs to the related Rosa and Rubus genera was investigated, ranging from 28.7% for genic-SSRs in rose to 16.1% for genomic-SSRs in raspberry. Among these markers, 33 and 16 were both localized in the diploid Fragaria reference map and cross-amplified in rose and raspberry, respectively. These results indicate that transferability of SSRs across the Rosoideae subfamily is limited. However, we have identified a set of Fragaria markers, polymorphic in the diploid reference population, which cross-amplified in both Rosa and Rubus, which represents a valuable tool for comparative mapping and genetic diversity analyses within the Rosoideae subfamily.     

VARIATION IN STRUCTURE AMONG FRUITS OF MALOIDEAE (ROSACEAE)

Fruits of Rosaceae subfamily Maloideae are known as pomes, a fruit type unique to the Maloideae. Using light microscopy we examined the pomes of 173 species, broadly representing the taxonomic diversity of the subfamily. Significant variation occurs among pomes in retention, orientation, and texture of calyx lobes on the distal end of the fruit; density and distribution of sclereids in the flesh; heterogeneity among flesh parenchyma cells; carpel number and number of ovules per carpel; degree of connation among the carpels and adnation between ovary and hypanthium; and texture of the core. Phenetic clustering closely links congeneric fruits. Sorbus is a notable exception; fruits of the compound-leaved species form a cluster unrelated to fruits of the simple-leaved species. Fruits of Malus are also heteromorphic. Division of the Maloideae into two tribes, Crataegeae and Sorbeae, based largely on texture of the core is not substantiated. We hypothesize that the ancestral pome had five carpels, minimal connation of carpels, minimal adnation of ovaries to the hypanthium, two ovules per carpel, and a leathery core. Various adaptations for frugivore dispersal of the seeds partially explain trends in pome evolution.     

A phylogenetic analysis of Prunus and the Amygdaloideae (Rosaceae) using ITS sequences of nuclear ribosomal DNA

The economically important plum or cherry genus (PRUNUS:) and the subfamily Amygdaloideae of the Rosaceae have a controversial taxonomic history due to the lack of a phylogenetic framework. Phylogenetic analysis using the ITS sequences of nuclear ribosomal DNA (nrDNA) was conducted to construct the evolutionary history and evaluate the historical classifications of PRUNUS: and the Amygdaloideae. The analyses suggest two major groups within the Amygdaloideae: (1) PRUNUS: s.l. (sensu lato) and MADDENIA:, and (2) EXOCHORDA:, Oemleria, and PRINSEPIA: The ITS phylogeny supports the recent treatment of including EXOCHORDA: (formerly in the Spiraeoideae) in the Amygdaloideae. MADDENIA: is found to be nested within PRUNUS: s.l. in the parsimony and distance analyses, but basal to PRUNUS: s.l. in the maximum likelihood analysis. Within PRUNUS:, two major groups are recognizable: (1) the AMYGDALUS:-PRUNUS: group, and (2) the CERASUS:-LAUROCERASUS:-PADUS: group. The clades in the ITS phylogeny are not congruent with most subgeneric groups in the widely used classification of PRUNUS: by Rehder. A broadly defined PRUNUS: is supported.     

Origin and Evolution of Rosaceae

Rosaceae. consisting of about 126 genera and 3200 species, is widely distributed in warm temperate and subtropical regions of the Northern Hemisphere, while more than half of the genera are Asiatic and more then 80% of the total number of Asiatic occur in China (Table 1). In this paper, the origin and evolution of Chinese genera is discussed mainly. The principal tendency of the whole family is also described from the point of view of evolution. First of all, the systematic position of Rosaceae in Angiospermae is reviewed. According to the records of paleobotany, rosaceous plants occurred first in the Tertiary, from the early period of Eocene (genera such as Spiraea and Prunus) to the late period of Miocene (e.g. Crataegus, Malus amd Rosa). They have quite a long history in geological data. Where has this big and old family originated and what steps does it stand in the long course of evolution of flowering plants? There are several opinions and explanations by different authors. In this paper, a general survey of the six prevailing classical systems (Table 2) is made to give a brief idea of the position of this family in the Angiospermae and of the relationships between the subfamilies and also the relationships between different genera in each subfamily. At the end of this paper, an attempt is made to analyse and sum up the major evolutionary tendency of the whole family. As generally condidered, Rosaceae originated from Magnoliales, and woody plants of the family still hold a dominant position. For instance, subfamily Spiraeoideae consists of only one herbaceous genus (i.e., Aruncus) and subfamily Rosoideae only a few herbaceous genera. All of these herbaceous genera are derived from the closely related woody genera of the same subfamily. In the course of evolution of Angiospermae, Rosaceae stands at the initial to the middle stages of development. All parts of plant body in this family are at the chang ing and developing stages, with carpels, fruits and inflorescences being the most active. The primitive types in this family, such as the members of subfamily Spiraeoideae, usually have 5 and free carpels, the number of which are either reduced to 2-1 or increased to 10-numerous. They have different levels of union and are either completely free from each other or coherent at base. The carpels usually occur on the upper part of the receptacle, because the shapes of receptacle are variable, sometimes disk-shaped, cupshaped, tube-shaped or even bottle-shaped. In the last case carpels grow inside the receptacle. Thus the position of carpels has changed from superior to inferior through halfsuperior. In accordance with the development of the carpels, various kinds of fruits are produced. The primitive types of fruit are follicles, with dry, dehiscent carpels opened along different sutures. The next step, the carpels have developed into an indehiscent, I-celled and l-seeded fruit, the so-caned achene. In different genera, the achenes have different coat types and appendages to facilitate dispersing the seeds. Some of the achenes grow upon the fleshy receptacle (like strawberry) and some of them inside the fleshy receptacle (like rose). Sometimes a few carpels are united with the receptacle and develop into a pome (like apple and pear). Another direction of the fruit development is the single carpel with fleshy exocarp and mesocarp, and a bony endocarp, then becoming a drupe (like peach and plum). In addition to fleshy receptacle of thickened fruit coats, they usually have showy colour, fragrant smell and also plenty of sugars, acids, vitamins, etc. which are edible and attract animals and human beings to assist the dispersion of seeds. In this family, there are various types of flower arrangements, both indefinite inflorescences including raceme, umbel, corymb and panicle, and the definite inflorescence, such as solitary flower, cyme and compound cyme. In the evolution course, they tend to change mostly from multiflowered compound inflorescence towards few-flowered simple inflorescence, and finally becoming a solitary flower: simultaneously with the decreasing of number of flowers on the inflorescence, the increasing of size of petals, which become very showy for attraction of insects so as to guarantee pollination and fertilization of the plants concerned. Another tendency, if the bisexual flowers change to unisexual, either monoecious- or dioecious-polygamous, then they form a dense spike which is beneficial to cross pollination. The abundance, diversity, and wide range of distribution of the species and genera of Rosaceae are considered mainly resulted from their highly developed reproductive organs.     

Phylogeny of subtribe Pyrinae (formerly the Maloideae, Rosaceae): Limited resolution of a complex evolutionary history

Generic relationships in the Pyrinae (equivalent to subfamily Maloideae) were assessed with six chloroplast regions and five nuclear regions. We also plotted 12 non-molecular characters onto molecular phylogenies. Chloroplast DNA trees are incongruent with those from nuclear regions, as are most nuclear regions with one another. Some of this conflict may be the result of hybridization, which occurs between many genera of Pyrinae in the present and may have occurred in the past, and duplication of nuclear loci. Sequence divergence between genera of Pyrinae, which is significantly less than that between genera of another large clade in Rosaceae, the Rosoideae, is concentrated in terminal branches, with short internal branches. This pattern is consistent with an ancient, rapid radiation, which has also been hypothesized from the fossil record. Even with about 500,000 bp of sequence, our results resolve only several small groups of genera and leave much uncertainty about phylogenetic relationships within Pyrinae.     

The origin of the apple subfamily (Maloideae; Rosaceae) is clarified by DNA sequence data from duplicated GBSSI genes

For 70 yr the leading hypothesis for the origin of the Maloideae has involved wide hybridization between ancestors of two other subfamilies. The basis of this hypothesis is that Maloideae have a base chromosome number of 17, whereas other Rosaceae are mostly x = 7, 8, or 9. To investigate this hypothesis we cloned and sequenced approximately 1.8 kilobases from the 5' portion of granule-bound starch synthase (GBSSI, or waxy) genes for 89 clones from 32 Rosaceae genera. Previous studies demonstrate the presence of two copies in all Rosaceae (GBSSI-1 and GBSSI-2) and four in Maloideae (GBSSI-1A, GBSSI-1B, GBSSI-2A, and GBSSI-2B). Parsimony and maximum likelihood analyses nest Gillenia, a genus of the southeastern United States with a base chromosome number of 9, within either Maloideae GBSSI-1 or GBSSI-2. Monophyly of Maloideae plus Gillenia is well supported by bootstrap values, loss of the sixth intron in all GBSSI-1 sequences, intron alignability between genera, and numerous nonmolecular characters. Our results falsify the wide-hybridization hypothesis and are consistent with a polyploid origin involving only members of a lineage that contained the ancestors of Gillenia. Under this hypothesis, the subfamily originated in North America, and the high Maloideae chromosome number arose via aneuploidy from x = 18.     

Rosaceae chemotaxonomy and the origins of the Pomoideae

The results of a chemotaxonomic survey of the Rosaceae for the occurrence of flavone C-g!ycosides, together with a general literature review of Rosaceae chemotaxonomy, are compared with the hypotheses of classical botanical taxonomy relating to the origins and evolution of the subfamilies of the Rosaceae. A tentative phyiogenetic scheme is presented, based upon all available taxonomic evidence. The chemotaxonomic data is consistent with the hypothesis that the Pomoideae are of allopolyploid origin, produced by ancient hybridization between primitive forms of the subfamilies Prunoideae and Spiraeoideae, although the possibility cannot completely be excluded that primitive Spiraeoideae only were involved. Flavone C-glycosides, hitherto thought to be restricted in the Rosaceae to Crataegus , have also been detected in the following genera: Pyracantha, Osteomeles, Aronia, Hesperomeles, Malacomeles, Chamaemetes, Dichotomanthes (Pomoideae); Quillafa (Spiraeoideae); Agrimonia, Adenostoma , doubtful traces in Sanguisorba, Potentilla, Alchemilla (Rosoideae). None could be detected in the Prunoideae. The chemotaxonomic evidence supports the hypothesis that Quillaja is a relict of an apocarpous ancestor of the Pomoideae and that Dichotomanthes is a relict of the primitive Pomoideae.     

The Evolution and Distribution of Subfam. Spiraeoideae (Rosaceae) of China,with Special Reference to Distribution of the Subfamily in the World

The subfam. Spiraeoideae, consisting of 22 genera and more than 260 species in the world,is the most primitive subfamily of Rosaceae. It has developed into two groups,i.e. evergreen and deciduous ones, of which eight genera and 100 species in China are totally deciduous. In the present paper, the origin,evolution and distribution of the Chinese genera is discussed mainly, and the distribution of the whole subfamily in the floristic regions of the world is also mentioned. Based on evolutionary trends of morphological characters, Spiraea L. is considered as the most primitive genus in the deciduous group of subfam. Spiraeoideae, from which some genera are been derived, the systematic position and evolutionary relationships between different genera are elucidated in this paper. Through the analysis on the geographical distribution of the genera in China, the areal types may be divided as follows: (1) North Temperate Type: Spiraea, Physocarpus, Aruncus. (2) East Asian and North American Disjunct Type: Sorbaria. (3) Mediterranean, West Asian (or Central Asia) and East Asian Type: Sibiraea. (4) Temperate Asian Type: Exochorda.(5) East Asian Type: (a) Sino Himalayan Distribution: Neillia; (b) Sino Japan Distribution: Stephanandra. After analysis of the distribution of subfam. Spiraeoideae in the world, it is shown that the Eastern Asiatic Region, being the richest in genera, species and endemic species of the world,is not only the center of distribution and differentiation,but also an important region for occurrence and development of some deciduous genera of this subfamily, while in North America, the Madrean Region and Rocky Mountain Region, genera, species and endemic species are abundant, which indicates that the western part of North America is also the distribution center of this subfamily at the present, but it may be the secondary center of distribution. It can be seen that the relatively primitive and evergreen g enera, i.e. Quillaja and Kageneckia, are now confined to South America. The fact implies that the South America may be the region for early differentiation and development of the evergreen genera in Subfam. Spiraeoideae. The analysis of Chinese plants has shown that China has the most members of the subfamily in Eastern Asiatic Region, with eight genera, 82 species and 62 endemic species and that the maximum concentration is in western Sichuan, northwestern Yunnan and their adjacent areas. It is very obvious that the center of distribution and diversity of Subfam. Spiraeoideae in China lies in the Hengduan Mountain Region of Sino Himalayan Forest Subkingdom and the western part of Sino Japan Forest Subkingdom, where may be the birthplace of some genera in China. It may be considered that the deciduous genera of Subfam. Spiraeoideae might have originated in Laurasia.According to the fossil records, the time of origin of Subfam.Spiraeoideae dates back to the Lower Cretaceous.     

中国蔷薇科绣线菊亚科的演化、分布——兼述世界绣线菊亚科植物的分布

绣线菊亚科是蔷薇科最原始的亚科,共有22属260余种, 包括常绿和落叶两大类群,前者是 原始类型。我国有8属100种,全都为落叶性。本文着重讨论中国各属的起源、演化和分布等 ,同时也概述全亚科植物在世界各植物区的分布等问题。绣线菊属Spiraea是该亚科落叶类群中最原始的属,它在早期发生趋异进化,衍生出形态各异而亲缘关系密切 的不同属,本文阐明了中国各属的系统位置和属间的亲缘关系。通过对我国各属地理分布的 分析对比,属的分布区可归纳为5个类型。对全球绣线菊亚科植物在世界各植物区中的属、种数统计表明,东亚区有8属105种,其中有96个特有种,是该亚科植物分布最多而又最集中 地区,具有在系统发育上处于各主要演化阶段的落叶类型,因此,东亚区是全球绣线菊亚科植 物的现代分布和分化中心,也是落叶类群发生和发展的关键地区。在北美洲,从马德雷区至落基山区一带分布着11属46种,均为特有种,显然北美洲西部也是该亚科植物的现代分布中心,但可能是第二分布中心。南美洲至今保存2个较古老的常绿属,即Quillaja和K ageneckia,基于此,南美洲可能是绣线菊亚科某些常绿属早期分化和发展的关键地区 。中国绣线菊亚科植物在东亚区占绝对优势,有8属82种,其中有62个特有种,分别占该区属 、种和 特有种数的100%、82%、和65%, 这些类群分布最密集地区是在中国喜马拉雅森林植物亚区 中的横断山脉地区和中国日本森林植物亚区的西部,这一带是中国绣线菊亚科的现代分布和多样性中心,很可能是某些属的发源地。由此看来,绣线菊亚科的落叶属可能起源于劳亚古陆。据化石记载,该亚科植物的起源时间可以追溯到白垩纪早白垩世。     

Pollen-expressed F-box gene family and mechanism of S-RNase-based gametophytic self-incompatibility (GSI) in Rosaceae

Many species of Rosaceae, Solanaceae, and Plantaginaceae exhibit S-RNase-based self-incompatibility (SI) in which pistil-part specificity is controlled by S locus-encoded ribonuclease (S-RNase). Although recent findings revealed that S locus-encoded F-box protein, SLF/SFB, determines pollen-part specificity, how these pistil- and pollen-part S locus products interact in vivo and elicit the SI reaction is largely unclear. Furthermore, genetic studies suggested that pollen S function can differ among species. In Solanaceae and the rosaceous subfamily Maloideae (e.g., apple and pear), the coexistence of two different pollen S alleles in a pollen breaks down SI of the pollen, a phenomenon known as competitive interaction. However, competitive interaction seems not to occur in the subfamily Prunoideae (e.g., cherry and almond) of Rosaceae. Furthermore, the effect of the deletion of pollen S seems to vary among taxa. This review focuses on the potential differences in pollen-part function between subfamilies of Rosaceae, Maloideae, and Prunoideae, and discusses implications for the mechanistic divergence of the S-RNase-based SI.     

Implications ofrbcL sequence data for higher order relationships of theLoasaceae and the anomalous aquatic plantHydrostachys (Hydrostachyaceae)

Subclass and ordinal relationships ofLoasaceae, a small predominately New World family, are examined usingrbcL sequence data. Sequences were examined for eight of the fifteen genera of theLoasaceae and the morphologically anomalous aquatic genusHydrostachys (Hydrostachyaceae). Parsimony analyses of these sequences, combined with previously publishedrcbL data, indicate thatLoasaceae belong in theCornales, and are the sister group ofHydrangeaceae. This agrees with phylogenies based on chloroplast DNA inverted repeat restriction site, morphological and chemical data. TherbcL trees support the monophyly of theLoasaceae and most generic relationships correspond to current subfamily divisions. TherbcL phylogeny also provides the first suggestion thatHydrostachys is allied with theHydrangeaceae in theCornales.     

Cloning and characterization of cDNAs encoding S-RNases from almond ( Prunus dulcis ): primary structural features and sequence diversity of the S-RNases in Rosaceae

cDNAs encoding three S-RNases of almond (Prunus dulcis), which belongs to the family Rosaceae, were cloned and sequenced. The comparison of amino acid sequences between the S-RNases of almond and those of other rosaceous species showed that the amino acid sequences of the rosaceous S-RNases are highly divergent, and intra-subfamilial similarities are higher than inter-subfamilial similarities. Twelve amino acid sequences of the rosaceous S-RNases were aligned to characterize their primary structural features. In spite of␣their high level of diversification, the rosaceous S-RNases were found to have five conserved regions, C1, C2, C3, C5, and RC4 which is Rosaceae-specific conserved region. Many variable sites fall into one region, named RHV. RHV is located at a similar position to that of the hypervariable region a (HVa) of the solanaceous S-RNases, and is assumed to be involved in recognizing S-specificity of pollen. On the other hand, the region corresponding to another solanaceous hypervariable region (HVb) was not variable in the rosaceous S-RNases. In the phylogenetic tree of the T2/S type RNase, the rosaceous S-RNase fall into two subfamily-specific groups (Amygdaloideae and Maloideae). The results of sequence comparisons and phylogenetic analysis imply that the present S-RNases of Rosaceae have diverged again relatively recently, after the divergence of subfamilies. Received: 28 May 1998 / Accepted: 13 August 1998