Bacteria have devised phosphotransfer signaling mechanisms for eliciting a variety of adaptive responses to their environment. These mechanisms are collectively referred to as two-component regulatory systems. Each system generally consists of a sensor protein histidine kinase, which is anchored in the cell membrane, and a cytoplasmic response regulator, whose activity is modulated by the sensor. Most response regulators are transcription factors. In this review, we briefly introduce the established concept on bacterial two-component regulatory systems, using the Agrobacterium VirA-VirG system as an example, and give the evidence for the existence of quite similar systems in higher plants, such as the signal transduction induced by the phytohormone cytokinin. The Arabidopsis CRE1 histidine kinase and its related proteins AHK2 and AHK3 perceive cytokinins in the environment and transduce a signal, presumably through the AHP bridge components that carry the histidine-containing phosphotransfer (HPt) domain, to the ARR1 response regulator that transcriptionally activates genes immediately responsive to cytokinins. In addition, this signal transfer process appears to participate in cross-talk with signaling systems that respond to daylight and another phytohormone, ethylene, through an intracellular pool of several ARR1-like molecular species and the AHP components.

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The dioecious plant Silene latifolia has both X and Y sex chromosomes. Male-specific random amplified polymorphic DNA (RAPD) fragments were analyzed to identify Y-chromosome-linked sequences. One of the RAPD fragments, MS4, was converted into a more reliable and reproducible sequence-tagged site (STS) marker. A set of MS4 STS primers was used to amplify two genomic DNA fragments (MS4a and MS4b) from a male plant and one (MS4a) from a female plant, which indicates that MS4b is located on the Y chromosome. Sequence analysis revealed that MS4a encoded a gag protein of a Ty3-gypsy-like retrotransposon. A 147-bp region from the middle of MS4a was deleted in MS4b. The MS4b sequence was not detected in the most closely related dioecious species, S. dioica. This suggests that a retrotransposon with the MS4b sequence has degenerated recently on the Y chromosome.

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Two new Fagopyrum (Polygonaceae) species, F. gracilipedoides and F. jinshaense, are described. Fagopyrum gracilipedoides was only found at Baoshan village, Lijiang district, Yunnan province, China. This species resembles the weedy species, F. gracilipes in morphology but they differ in both mating system and ploidy level; F. gracilipedoides is a heterostylous self-incompatible diploid species (2n = 16), whereas F. gracilipes is a self-compatible tetraploid species (2n = 32). Fagopyrum jinshaense was found along the Jinsha River valley near the border of Sichuan, Yunnan, and Tibet in China. Fagopyrum jinshaense is morphologically similar to F. gilesii, but they differ in the morphology of their inflorescences. Fagopyrum jinshaense has long spike-like inflorescences, whereas F. gilesii has a compact head-like one. Both F. jinshaense and F. gilesii are self-incompatible with heterostylous flowers and are diploid. Interspecific crosses between the two new species and already known species in the urophyllum group of Fagopyrum resulted in the production of self- and cross-sterile hybrids in the species combinations attempted. These results indicated that both new species are reproductively isolated from other Fagopyrum species. Molecular phylogenetic analysis based on the nucleotide sequence of the trnK gene intron in chloroplast DNA revealed the following points: 1) F. gracilipedoides , F. rubifolium and F. gracilipes / F. capillatum showed a trifurcating relationship and 2) F. jinshaense formed a clade with F. pleioramosum, F. callanthum, and F. macrocarpum, and was only distantly related to F. gilesii. In the clade of F. capillatum, F. gracilipes, F. gracilipedoides and F. rubifolium, the breakdown of self-incompatibility accompanying genome duplication seems to have occurred twice independently.

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This article comprises our final remarks on the phenotypic effects of alien plasmons on common wheat. Twenty-one vegetative, reproductive, and seed characters of 551 alloplasmic lines of 12 common wheat genotypes with 46 alloplasmons, and as the control, their euplasmic lines were investigated. Effects of genotype, plasmon, and their interaction had high statistical significance for all the characters investigated, whereas phenotypic variations attributable to the alien plasmons were relatively small. Individual plasmon types are characterized by their primary effects on 21 characters. Genotype x plasmon effects on two representative characters, heading date and plant height, are described in detail. Cluster and principal component analyses of the phenotypic effects of the 47 plasmons yielded 22 groups. The relationships between these phenotype-based groups and those defined by molecular differences in organellar genomes were examined. A significant correlation was found with some explainable discrepancies. For efficient plasmon identification, use of six of the present 12 genotypes is proposed. The key for plasmon classification is provided. Our findings indicate that alien plasmons may be of limited value in future wheat breeding, but that the plasmon diversity that exists in Triticum and Aegilops species is of great significance for understanding the evolution of these genera.

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With the aim of broadening the gene pool of Triticeae for crop improvement, the genetic diversity of three hexaploid Elymus species indigenous to Japan and East Asia (E. tsukushiensis, E. humidus and E. dahuricus) was evaluated using amplified fragment length polymorphism (AFLP) markers. A total of 34 accessions: five of E. tsukushiensis, 13 of E. humidus, 15 of E. dahuricus, and one tetraploid Elymus species as an outgroup, were analyzed. The AFLP analysis was conducted with 12 selective primer combinations. In all, 329 bands were scored. The average number of bands scored per accession was 135.3. Among the 34 accessions, no polymorphism was detected among 10 accessions of E. humidus and among three accessions of E. tsukushiensis. Each species showed a diagnostic band pattern. One accession of E. humidus showed a band pattern intermediate between those of E. humidus and E. tsukushiensis, suggesting the occurrence of interspecific introgression. The level of intraspecific variation was highest in E. dahuricus (1-psb = 0.17, π = 0.010), followed by E. tsukushiensis (1-psb = 0.14, π = 0.008) and E. humidus (1-psb = 0.03, π = 0.002). The level of interspecific variation was higher than that of intraspecific variation in all the pairs compared. The level of divergence between E. humidus and E. tsukushiensis was relatively low, but even so it was two times higher than that of the intraspecific variation for each species. The phylogenetic tree constructed here showed clear separations of all the species. The results of this study indicate a clear divergence of E. humidus from E. tsukushiensis in spite of the morphological similarity between these two species. Based on the values of nucleotide diversity, the time of divergence between E. humidus and E. tsukushiensis was estimated to be 0.9-1.2 million years ago.

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