Speciation process of <Emphasis Type="Italic">Salvia isensis</Emphasis> (Lamiaceae), a species endemic to serpentine areas in the Ise-Tokai district,Japan, from the viewpoint of the contradictory phylogenetic trees generated from chloroplast and nuclear DNA

To understand the speciation process of Salvia isensis (Lamiaceae), a species endemic to a special environment (serpentine areas in the Ise-Tokai district, central Honshu, Japan), chloroplast DNA (cpDNA) and nuclear ribosomal DNA (nrDNA) were employed to analyze the phylogenetic relationships of S. isensis with related species in Japan. Allozymic polymorphisms were also used to analyze genetic relationships among Salvia species. A contradiction in the phylogenetic positions of species studied was detected when phylogenetic trees were constructed using cpDNA or nrDNA, i.e., S. isensis was a sister to the other species in phylogenetic trees generated from cpDNA, while S. japonica was a sister to the other species in the case of nrDNA. Genetic relationships between Salvia species estimated from allozymic polymorphisms did not contradict to the topology for nrDNA. Using the present results, the speciation process of S. isensis is discussed with regard to introgressive gene exchanges between related species. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Phylogeny of <Emphasis Type="Italic">Litsea</Emphasis> and related genera (Laureae-Lauraceae) based on analysis of <Emphasis Type="Italic">rpb2</Emphasis> gene sequences

The relationship between Litsea and related genera is currently unclear. Previous molecular studies on these taxa using cpDNA and nrITS were unable to produce well-resolved phylogenetic trees. In this study, we explored the potential of the rpb2 gene as a source of molecular information to better resolve the phylogenetic analysis. Although rpb2 was believed to be a single-copy gene, our cloning results showed that most species examined possessed several copies of these sequences. However, the genetic distance among copies from any one species was low, and these copies always formed monophyletic groups in our molecular trees. Our phylogenetic analyses of rpb2 data resulted in better resolved tree topologies compared to those based on cpDNA or nrITS data. Our results show that monophyly of the genus Litsea is supported only for section Litsea. As a genus, Litsea was shown to be polyphyletic. The genera Actinodaphne and Neolitsea were resolved as monophyletic groups in all analyses. They were also shown to be sisters and closer to the genus Lindera than to the genus Litsea. Our results also revealed that the genus Lindera is not a monophyletic group.     

Chloroplast DNA phylogeography of <Emphasis Type="Italic">Pedicularis</Emphasis> ser. <Emphasis Type="Italic">Gloriosae</Emphasis> (Orobanchaceae) in Japan

Phylogeographic analyses using chloroplast DNA (cpDNA) variation were performed for Pedicularis ser. Gloriosae (Orobanchaceae). Eighty-one plants of 18 populations of 6 species (P. gloriosa, P. iwatensis, P. nipponica, P. ochiaiana, P. sceptrum-carolinum and P. grandiflora) were analyzed. Fifteen distinct haplotypes were identified based on six cpDNA regions: the intergenic spacer between the trnT and trnL 3′exon, trnL 3′exon-trnF, atpB-rbcL, accD–psaI, the rpl16 intron and the trnK region (including the matK gene). Via phylogenetic analyses of the haplotypes, two continental species, P. sceptrum-carolinum and P. grandiflora, were placed at the most ancestral position in the trees. The former species is widely distributed in the Eurasian continent, and the latter is distributed in Far East Asia. Two robust major cpDNA clades (clades I and II) were revealed in the Japanese archipelago, although the statistical values of monophyly of these clades were weak. Clade I included the haplotypes (A-1, A-2, B-1, B-2 and J) of three species (P. gloriosa, P. iwatensis and P. ochiaiana), and Clade II included seven haplotypes (C-D, E-1, E-2 and F-H) of P. nipponica. These results suggest that this series originated on the Eurasian continent and that subsequently populations at the eastern edge of the continent differentiated into the two Japanese lineages. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The use of <Emphasis Type="Italic">gyrB</Emphasis> sequence analysis in the phylogeny of the genus <Emphasis Type="Italic">Amycolatopsis</Emphasis>

Partial gyrB sequences (>1 kb) were obtained from 34 type strains of the genus Amycolatopsis. Phylogenetic trees were constructed to determine the effectiveness of using this gene to predict taxonomic relationships within the genus. The use of gyrB sequence analysis as an alternative to DNA–DNA hybridization was also assessed for distinguishing closely related species. The gyrB based phylogeny mostly confirmed the conventional 16S rRNA gene-based phylogeny and thus provides additional support for certain of these 16S rRNA gene-based phylogenetic groupings. Although pairwise gyrB sequence similarity cannot be used to predict the DNA relatedness between type strains, the gyrB genetic distance can be used as a means to assess quickly whether an isolate is likely to represent a new species in the genus Amycolatopsis. In particular a genetic distance of >0.02 between two Amycolatopsis strains (based on a 315 bp variable region of the gyrB gene) is proposed to provide a good indication that they belong to different species (and that polyphasic taxonomic characterization of the unknown strain is worth undertaking). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. The GenBank accession numbers for the gyrB gene sequences obtained in this study are shown in Table 1.     

Geographic variability in mitochondrial introgression among hybridizing populations of Golden-winged (<Emphasis Type="Italic">Vermivora chrysoptera</Emphasis>) and Blue-winged (<Emphasis Type="Italic">V.opinus</Emphasis>) Warblers

The rapidly declining Golden-winged Warbler (Vermivora chrysoptera) is of conservation concern owing in part to hybridization with the closely related Blue-winged Warbler (V. pinus). These species hybridize extensively in eastern North America and over the past century the Blue-winged Warbler has displaced the Golden-winged Warbler from substantial regions of its historic breeding range. A previous study suggested that these genetic interactions result in rapid and asymmetric introgression of Blue-winged Warbler mitochondrial DNA (mtDNA) into Golden-winged phenotype populations within the zones of contact, but more recent and extensive surveys have documented a more complex pattern of genetic interchange between these taxa. We surveyed mtDNA/phenotype associations in 104 individuals of known phenotype drawn from two locations with different histories of contact and found substantial variation between sites in the extent of introgression. Where both species have co-existed for more than a century, we found evidence of bi-directional introgression and the long-term persistence of Golden-winged mtDNA haplotypes. At the leading edge of the northward expansion of Blue-winged Warblers, we found predominantly Golden-winged Warbler mtDNA haplotypes in both Golden-winged and hybrid-phenotype individuals. Across both sites, genetic swamping does not appear to be occurring via the early immigration of Blue-winged Warbler females into populations dominated by Golden-winged Warbler phenotypes. Instead, the differing patterns of mitochondrial introgression may be driven by the relative local population sizes of the parental species coupled with subtle between-species differences in mate choice and habitat preferences.     

<Emphasis Type="Italic">Drosophila</Emphasis><Emphasis Type="Italic">P</Emphasis> transposons of the urochordata <Emphasis Type="Italic">Ciona intestinalis</Emphasis>

P transposons belong to the eukaryotic DNA transposons, which are transposed by a cut and paste mechanism using a P-element-coded transposase. They have been detected in Drosophila, and reside as single copies and stable homologous sequences in many vertebrate species. We present the P elements Pcin1, Pcin2 and Pcin3 from Ciona intestinalis, a species of the most primitive chordates, and compare them with those from Ciona savignyi. They showed typical DNA transposon structures, namely terminal inverted repeats and target site duplications. The coding region of Pcin1 consisted of 13 small exons that could be translated into a P-transposon-homologous protein. C. intestinalis and C. savignyi displayed nearly the same phenotype. However, their P elements were highly divergent and the assumed P transposase from C. intestinalis was more closely related to the transposase from Drosophila melanogaster than to the transposase of C. savignyi. The present study showed that P elements with typical features of transposable DNA elements may be found already at the base of the chordate lineage. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

<Emphasis Type="Italic">RNase</Emphasis>-Based Gametophytic Self-Incompatibility Evolution: Questioning the Hypothesis of Multiple Independent Recruitments of the <Emphasis Type="Italic">S</Emphasis>-Pollen Gene

Multiple independent recruitments of the S-pollen component (always an F-box gene) during RNase-based gametophytic self-incompatibility evolution have recently been suggested. Therefore, different mechanisms could be used to achieve the rejection of incompatible pollen in different plant families. This hypothesis is, however, mainly based on the interpretation of phylogenetic analyses, using a small number of divergent nucleotide sequences. In this work we show, based on a large collection of F-box S-like sequences, that the inferred relationship of F-box S-pollen and F-box S-like sequences is dependent on the sequence alignment software and phylogenetic method used. Thus, at present, it is not possible to address the phylogenetic relationship of F-box S-pollen and S-like sequences from different plant families. In Petunia and Malus/Pyrus the putative S-pollen gene(s) show(s) variability patterns different than expected for an S-pollen gene, raising the question of false identification. Here we show that in Petunia, the unexpected features of the putative S-pollen gene are not incompatible with this gene’s being the S-pollen gene. On the other hand, it is very unlikely that the Pyrus SFBB-gamma gene is involved in specificity determination. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The genetic structure of endangered indigenous populations of the amago salmon, <Emphasis Type="Italic">Oncorhynchus</Emphasis><Emphasis Type="Italic">masou</Emphasis><Emphasis Type="Italic">ishikawae</Emphasis>, in Japan

The amago salmon, Oncorhynchus masou ishikawae, is an endemic subspecies of O. masou in Japan. Owing to the extensive stocking of hatchery fish throughout Japan, indigenous populations of O. m. ishikawae are now on the verge of extinction. We examined the genetic effects of stocking hatchery fish on wild populations in the River Koza, Japan, using microsatellite and mitochondrial DNA (mtDNA) markers. For mtDNA, haplotype mt1, which is common in wild populations, was present exclusively in isolated wild populations assumed to be unaffected by previous stocking, while it was never observed in hatchery fish. Genetic diversity was much higher in wild populations in the stocked area, which shared many mtDNA haplotypes with hatchery fish, than in isolated wild populations with haplotype mt1. Pairwise F _ST estimates based on microsatellites showed significant differentiation among the isolated populations with many microsatellite loci monomorphic. Significant deviation from Hardy–Weinberg equilibrium was observed in wild populations in the area subject to stocking, where a Bayesian-based assignment test showed a high level of introgression with hatchery fish. These results suggest that wild populations with haplotype mt1, which became isolated through anthropogenic environmental change in the 1950–1960s, represent indigenous populations of O. m. ishikawae in the River Koza. They have low genetic diversity, most likely caused by genetic bottlenecks following damming and environmental deterioration, while stocking of hatchery fish over the past 30 years apparently had a large impact on the genetic structure of wild populations in the main channel of the River Koza.     

Mutational analysis of the <Emphasis Type="Italic">gum</Emphasis> gene cluster required for xanthan biosynthesis in <Emphasis Type="Italic">Xanthomonas</Emphasis><Emphasis Type="Italic">oryzae</Emphasis> pv <Emphasis Type="Italic">oryzae</Emphasis>

Genome sequence analysis of Xanthomonas oryzae pv. oryzae has revealed a cluster of 12 ORFs that are closely related to the gum gene cluster of Xanthomonas campestris pv. campestris. The gum gene cluster of X. oryzae encodes proteins involved in xanthan production; however, there is little experimental evidence supporting this. In this study, biochemical analyses of xanthan produced by a defined set of X. oryzae gum mutant strains allowed us to preliminarily assign functions to most of the gum gene products: biosynthesis of the pentasaccharide repeating unit for GumD, GumM, GumH, GumK, and GumI, xanthan polymerization and transport for GumB, GumC, GumE, and GumJ, and modification of the pentasaccharide repeating unit for GumF, GumG, and GumL. In addition, we found that the exopolysaccharides are essential but not specific for the virulence of X. oryzae. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Sang-Yoon Kim and Jeong-Gu Kim contributed equally to this work.     

Phylogenetic relationships among subgenera,species, and varieties of Japanese <Emphasis Type="Italic">Salvia</Emphasis> L. (Lamiaceae)

To determine evolutionary relationships among all Japanese members of the genus Salvia (Lamiaceae), we conducted molecular phylogenetic analyses of two chloroplast DNA (cpDNA) regions (rbcL and the intergenic spacer region of trnL−trnF:trnL−trnF) and one nuclear DNA (nrDNA) region (internal transcribed spacer, ITS). In cpDNA, nrDNA, and cpDNA+nrDNA trees, we found evidence that all Japanese and two Taiwanese Salvia species are included in a clade with other Asian Salvia, and Japanese Salvia species were distributed among three subclades: (1) S. plebeia (subgenus Sclarea), (2) species belonging to subg. Salvia, and (3) species belonging to subg. Allagospadonopsis. At the specific level our findings suggest: a close relationship between S. nipponica and S. glabrescens, no support for monophyly of S. lutescens and its varieties in cpDNA, nrDNA and cpDNA+nrDNA trees, and that S. pygmaea var. simplicior may be more closely related to S. japonica than to other varieties of S. pygmaea.     

mtDNA Diversity and genetic lineages of eighteen cattle breeds from <Emphasis Type="Italic">Bos taurus </Emphasis>and<Emphasis Type="Italic"> Bos indicus</Emphasis> in China

In order to clarify the origin and genetic diversity of indigenous cattle breeds in China, we carried out phylogenetic analysis of representatives of those breeds by employing mitochondrial gene polymorphism. Complete cyt b gene sequences, 1140 bp in length, were determined for a total of 136 individuals from 18 different breeds and these sequences were clustered into two distinct genetic lineages: taurine (Bos taurus) and zebu (Bos indicus). In analysis of the cyt b gene diversity, Chinese cattle showed higher nucleotide (0.00923) and haplotype diversity (0.848) than the reports from other studies, and the animals from the taurine lineage indicated higher nucleotide diversity (0.00330) and haplotype diversity (0.746) than the ones from the zebu lineage (0.00136; 0.661). The zebu mtDNA dominated in the southern breeds (63.3–100%), while the taurine dominated in the northern breeds (81.8–100%). Six cattle breeds from the central area of China exhibited intermediate frequencies of zebu mtDNA (25–71.4%). This polymorphism revealed a declining south-to-north gradient of female zebu introgression and a geographical hybrid zone of Bos taurus and Bos indicus in China.     

Marked Intragenomic Heterogeneity and Geographical Differentiation of nrDNA ITS in <Emphasis Type="BoldItalic">Larix</Emphasis><Emphasis Type="BoldItalic">potaninii</Emphasis> (Pinaceae)

Nuclear ribosomal DNA (nrDNA) of gymnosperms, especially Pinaceae, is characterized by slow concerted evolution and exhibits substantial ITS-region length variation (975–3663 bp), in sharp contrast to the narrow range (565–700 bp) in angiosperms. Here we examined intra- and intergenomic heterogeneity of the nrDNA internal transcribed spacer (ITS) region in four varieties of Larix potaninii, a species from the mountainous areas of western China. Two clones with more than a 100-bp deletion in ITS1 were detected in L. potaninii var. chinensis and L. potaninii var. australis, respectively. The deletion resulted in the loss of most part, including the motif sequence, of subrepeat 1 (SR1). Sequence divergence and phylogenetic analyses showed that some clones would be pseudogenes given their low GC content, high substitution rates, unique positions in the phylogenetic trees, or significant length variation. These clones might represent orphons or paralogues at minor loci resulting from large-scale gene or chromosome reorganization. Some recombinants characterized by chimeric structure and discordant phylogenetic positions in partitioned sequence analyses indicate that unequal crossing-over plays an important role in the process of nrDNA concerted evolution. In addition, some varieties of L. potaninii might have experienced an nrDNA founder effect parallel to their geographical isolation.     

Comparison of Defense Body Movements of <Emphasis Type="Italic">Apis laboriosa</Emphasis>, <Emphasis Type="Italic">Apis dorsata dorsata</Emphasis> and <Emphasis Type="Italic">Apis dorsata breviligula</Emphasis> Honey Bees

Defense behavior of three, free living giant (Megapis) honey bee subspecies, Apis laboriosa, A. dorsata dorsata and A. dorsata breviligula, was compared. Disturbed worker bees responded with characteristic dorso-ventral defense body twisting (DBT). Workers of A. laboriosa twisted the thorax by 55°, and the two other A. dorsata subspecies by about 10° more. A. laboriosa workers raised the tip of the abdomen by 90° and workers of the two other bee subspecies by about 20° higher. Differences in those traits were highly significant between A. laboriosa and both A. dorsata subspecies, but were not significant between those two subspecies. The whole cycle of DBT was the most vigorous in A. d. breviligula (0.11 s), and it was twice as vigorous as in A. d. dorsata (0.26 s) and trice as in A. laboriosa (0.32 s). A. laboriosa twisted the body together with wings folded over the abdomen, while the two A. dorsata subspecies raised the abdomen between spread wings. This supports the opinion to treat A. laboriosa as a separate species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Ectomycorrhizal characterization of an American chestnut <Emphasis Type="SmallCaps">(</Emphasis><Emphasis Type="Italic">Castanea dentata</Emphasis><Emphasis Type="SmallCaps">)</Emphasis>-dominated community in Western Wisconsin

Circa 1900, a farmer from the eastern US planted 11 American chestnut (Castanea dentata) seeds on a newly established farm near West Salem in western Wisconsin. These trees were very successful, producing a large stand of over 6,000 trees. Since this area is well outside the natural range of chestnut, these trees remained free from chestnut blight until 1987. In the West Salem stand, chestnuts are the dominant species of a mixed forest community, reminiscent of the chestnut–oak ecosystems of pre-1900 Appalachia. To identify putative mycorrhizal associates of chestnut in this unique forest, our approach was twofold: (1) an extensive fruiting body survey was conducted for four seasons that yielded approximately 100 putative mycorrhizal species and (2) a belowground molecular approach was used to generate DNA sequences of the internal transcribed spacer region from ectomycorrhizae. Unexpectedly, chestnut did not appear to be the dominant underground ectomycorrhizal-forming plant species. This study highlights the need to identify the plant host species when conducting belowground molecular-based surveys and provides preliminary identification of ectomycorrhizal fungi associated with a disjunct stand of American chestnut. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Chloroplast DNA inheritance and variation in <Emphasis Type="Italic">Leucadendron</Emphasis> species (Proteaceae) as revealed by PCR-RFLP

The inheritance of chloroplast DNA (cpDNA) in Leucadendron species was studied by polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) analysis. A total of 100 progeny from five interspecific crosses involving seven parental species were tested, and all progeny exhibited the cpDNA restriction fragment pattern of the female parent, indicating that cpDNA in Leucadendron is maternally inherited. PCR-RFLP was also employed to study cpDNA variation among 21 Leucadendron species. Parsimony analysis using a heuristic search resulted in a phylogenetic tree that showed limited agreement to the taxonomic classification of Leucadendron species, based on morphological characteristics. The incongruence between cpDNA phylogenetic and taxonomic groupings in Leucadendron may be due to reticulate evolution involving a combination of hybridization and introgression, convergent evolution and/or lineage sorting at the interspecific, intersubsectional and intersectional levels.     

A PCR survey of <Emphasis Type="Italic">Hox</Emphasis> genes in the myzostomid <Emphasis Type="Italic">Myzostoma cirriferum</Emphasis>

Using degenerate primers, we were able to identify seven Hox genes for the myzostomid Myzostoma cirriferum. The recovered fragments belong to anterior class (Mci_lab, Mci_pb), central class (Mci_Dfd, Mci_Lox5, Mci_Antp, Mci_Lox4), and posterior class (Mci_Post2) paralog groups. Orthology assignment was verified by phylogenetic analyses and presence of diagnostic regions in the homeodomain as well as flanking regions. The presence of Lox5, Lox4, and Post2 supports the inclusion of Myzostomida within Lophotrochozoa. We found signature residues within flanking regions of Lox5, which are also found in annelids, but not in Platyhelminthes. As such the available Hox genes data of myzostomids support an annelid relationship. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A new strain of <Emphasis Type="Italic">Arthrinium phaeospermum</Emphasis> isolated from <Emphasis Type="Italic">Carex kobomugi</Emphasis> Ohwi is capable of gibberellin production

Plant growth-promoting endophytic fungi with gibberellin-producing ability were isolated from the roots of Carex kobomugi Ohwi, a common sand-dune plant, and bioassayed for plant growth-promotion. A new strain, Arthrinium phaeospermum KACC43901, promoted growth of waito-c rice and Atriplex gemelinii. Analysis of its culture filtrate showed the presence of bioactive GA₁ (0.5 ng/ml), GA₃ (8.8 ng/ml), GA₄ (4.7 ng/ml) and GA₇ (2.2 ng/ml) along with physiologically inactive GA₅ (0.4 ng/ml), GA₉ (0.6 ng/ml), GA₁₂ (0.4 ng/ml), GA₁₅ (0.4 ng/ml), GA₁₉ (0.9 ng/ml) and GA₂₄ (1.8 ng/ml). The fungal isolate was identified through sequence homology and phylogenetic analysis of 18S rDNA (internal transcribed region). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Study of tauopathies by comparing <Emphasis Type="Italic">Drosophila</Emphasis> and human <Emphasis Type="Italic">tau</Emphasis> in <Emphasis Type="Italic">Drosophila</Emphasis>

The microtubule-binding protein tau has been investigated for its contribution to various neurodegenerative disorders. However, the findings from transgenic studies, using the same tau transgene, vary widely among different laboratories. Here, we have investigated the potential mechanisms underlying tauopathies by comparing Drosophila (d-tau) and human (h-tau) tau in a Drosophila model. Overexpression of a single copy of either tau isoform in the retina results in a similar rough eye phenotype. However, co-expression of Par-1 with d-tau leads to lethality, whereas co-expression of Par-1 with h-tau has little effect on the rough eye phenotype. We have found analogous results by comparing larval proteomes. Through genetic screening and proteomic analysis, we have identified some important potential modifiers and tau-associated proteins. These results suggest that the two tau genes differ significantly. This comparison between species-specific isoforms may help to clarify whether the homologous tau genes are conserved. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. This study was supported by the National Science Foundation of China (30270341; 30630028), the Multidisciplinary Program (Brain and Mind) of the Chinese Academy of Sciences, the Major State Basic Research Program (“973 program”; G2000077800; G2006CB806600; 2006CB911003), the Precedent Project of Important Intersectional Disciplines in the Knowledge Innovation Engineering of the Chinese Academy of Sciences (KJCX1-09-03).     

Discrimination among <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> H serotypes,serovars and strains based on 16S rRNA, <Emphasis Type="Italic">gyrB</Emphasis> and <Emphasis Type="Italic">aroE</Emphasis> gene sequence analyses

Our aim was to investigate the capability of each of three genes, 16S rRNA, gyrB and aroE, to discriminate, first, among Bacillus thuringiensis H serotypes; second, among B. thuringiensis serovars from the same H serotype; and third, among B. thuringiensis strains from the same serovar. The 16S rRNA, gyrB and aroE genes were amplified from 21 B. thuringiensis H serotypes and their nucleotide sequences determined. Additional strains from four B. cereus sensu lato species were included for comparison purposes. These sequences were pair-wise compared and phylogenetic relationships were revealed. Each of the three genes under study could discriminate among B. thuringiensis H serotypes. The gyrB and aroE genes showed a discriminatory power among B. thuringiensis H serotypes up to nine fold greater than that of the 16S rRNA gene. The gyrB gene was retained for subsequent analyses to discriminate B. thuringiensis serovars from the same H serotype and to discriminate strains from same serovar. A total of 42 B. thuringiensis strains, which encompassed 25 serovars from 12 H serotypes, were analyzed. The gyrB gene nucleotide sequences were different enough as to be sufficient to discriminate among B. thuringiensis serovars from the same H serotype and among B. thuringiensis strains from the same serovar. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

<Emphasis Type="Italic">FORMOSA</Emphasis> controls cell division and expansion during floral development in <Emphasis Type="Italic">Antirrhinum</Emphasis><Emphasis Type="Italic">majus</Emphasis>

Control of organ size is the product of coordinated cell division and expansion. In plants where one of these pathways is perturbed, organ size is often unaffected as compensation mechanisms are brought into play. The number of founder cells in organ primordia, dividing cells, and the period of cell proliferation determine cell number in lateral organs. We have identified the Antirrhinum FORMOSA (FO) gene as a specific regulator of floral size. Analysis of cell size and number in the fo mutant, which has increased flower size, indicates that FO is an organ-specific inhibitor of cell division and activator of cell expansion. Increased cell number in fo floral organs correlated with upregulation of genes involved in the cell cycle. In Arabidopsis the AINTEGUMENTA (ANT) gene promotes cell division. In the fo mutant increased cell number also correlates with upregulation of an Antirrhinum ANT-like gene (Am-ANT) in inflorescences that is very closely related to ANT and shares a similar expression pattern, suggesting that they may be functional equivalents. Increased cell proliferation is thought to be compensated for by reduced cell expansion to maintain organ size. In Arabidopsis petal cell expansion is inhibited by the BIGPETAL (BPE) gene, and in the fo mutant reduced cell size corresponded to upregulation of an Antirrhinum BPE-like gene (Am-BPE). Our data suggest that FO inhibits cell proliferation by negatively regulating Am-ANT, and acts upstream of Am-BPE to coordinate floral organ size. This demonstrates that organ size is modulated by the organ-specific control of both general and local gene networks. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.