Numerous cultivars of cyclamen have been developed by improving wild plants of Cyclamen persicum, and they are now among the most important pot plants. However, no cultivars have yet been produced in the other 21 Cyclamen species. Furthermore, these 21 wild species have not yet been used for improving C. persicum cultivars due to hybrid inviability and hybrid sterility. In recent studies, hybrid inviability caused by abortion of hybrid embryos was overcome by an embryo rescue technique involving culture of ovules with placenta, which resulted in the production of interspecific hybrids between C. persicum and each of ten wild species. Hybrid sterility caused by abnormal meiotic chromosome behavior in hybrids (allodiploids) between diploid C. persicum and each of two diploid wild species was overcome by chromosome doubling using in vitro colchicine treatment, resulting in the production of two types of fertile amphidiploids (allotetraploids). On the other hand, three types of allotetraploids were produced between autotetraploid cultivars of C. persicum and each of three autotetraploid wild species by the embryo rescue technique without chromosome doubling. Embryo rescue and in vitro chromosome doubling are simple and useful methods for overcoming hybrid inviability and hybrid sterility in interspecific hybridization in the genus Cyclamen. Some of the fertile amphidiploids thus produced have already been incorporated into commercial breeding of novel types of cyclamens with important traits such as flower fragrance and disease resistance.
The genus Primula (Primulaceae) consists of approximately 420 species that mainly inhabit temperate to cold regions of the Northern hemisphere. Although most species have attractive flowers with high ornamental value, few have been cultivated as ornamental plants. To develop novel ornamental crops and to introduce novel useful characters, these unexploited rich germplasms of the genus Primula have the potential to serve as breeding materials through the use of interspecific hybridization. However, interspecific hybrids of this genus have rarely been produced, and embryo rescue is one of the most useful strategies to overcome the difficulty of achieving successful hybridization, especially in wide crosses. In recent studies, we successfully obtained various interspecific hybrids in wide cross combinations in Primula using the embryo rescue technique, and showed that unexpected polyploid hybrids were frequently produced by the fertilization of unreduced female and/or male gametes, which were formed in most of the species examined. Some of the resultant hybrids have useful and attractive characters, and they have already been used directly as novel cultivars or incorporated into commercial breeding of novel types of primulas.
In the genus Hydrangea, H. macrophylla is the most popular species. For this species, numerous cultivars with showy colorful flowers have been bred since the early 1900s through selection of natural mutants and intraspecific crosses among a limited number of early ancestral varieties. Although breeding of H. macrophylla has been successful, further improvements in flower shape, flower color, and growth habit are desirable. H. scandens ssp. chinensis is a small shrub that is native to South and Southeast Asia and valued for its evergreen foliage, winter flowering and broad adaptability in mild climates. Cross-pollination between H. scandens ssp. chinensis and H. macrophylla, and subsequent ovule culture, resulted in the production of an interspecific hybrid plant. The hybridity of this plant was confirmed by RAPD analysis. The hybrid plant had flower and leaf morphologies intermediate between the two parental species. Since the hybrid showed more vigorous growth than both parents, had evergreen foliage, and flowered in winter, it has sufficient horticultural merit for commercialization and may be suitable for greenhouse culture.
To diversify flower color and growth habit of marguerite (Argyranthemum frutescens), intergeneric crossing was carried out using marguerite as the seed parent and annual chrysanthemum (Glebionis carinatum) or crown daisy (G. coronaria) as the pollen parent. After cross-pollination, seedlings were successfully obtained by applying ovule culture. Ovule culture-derived plants showed novel characteristics in flower shape and color (orange, reddish brown, or wisteria pink) that are not observed in marguerite. Some also showed novel flowering habits such as perpetual flowering. The results indicate that these ovule culture-derived plants were intergeneric hybrids and that the hybrids obtained in the present study may be useful for further breeding of marguerite, especially for introducing valuable characteristics such as a wide range of flower color.
Torenia is an annual plant of the family Scrophulariaceae that is used as an ornamental summer bedding plant. Torenia is also an experimental plant with several useful characteristics, i.e., ease of genetic transformation, ability to differentiate adventitious structures, protruding embryo sac, and capacity for in vitro flowering. Genetic transformation of torenia was first reported in 1995, and it has been used in various transgenic studies. Torenia is a useful model plant for transgenic studies on ornamental plant characteristics such as the color, shape, and longevity of flowers. In this paper, the characteristics of torenia as an experimental plant and the transgenic studies performed with torenia are reviewed.
The reaction of 9-hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid (KODA) and catecholamine in water (pH 8.0) in vitro generates many products, and we have shown that the major adduct FN1 among the reactants of KODA and norepinephrine is a potent inducer of floral differentiation in Lemna (L.) paucicostata 151 [Yokoyama et al. (2000) Plant Cell Physiol 41: 110–113, Yamaguchi et al. (2001) ibid 42: 1201–1209]. Since such reactants may be involved in flower induction in vivo, it is of interest to elucidate the structure-activity relationships among the reactants to throw light on the nature of the putative active site. Here, we report two other adducts, designated as FN7 and FN10. They are structurally similar to FN1, having a tricyclic structure with 12-cis-olefin conjugated with noradrenochrome. FN10 was a more potent inducer than FN1. These results are consistent with the hypothesis that tricyclic KODA/norepinephrine adducts play an important role in flower-induction in L. paucicostata, strain 151.
Untranslated regions of eukaryotic genes contain elements that in combination with proteins/RNAs modulate translation of individual messenger RNAs. Elements present in 5′-UTRs that influence translational efficiency include AUG sequence context, and presence of uAUGs/uORFs. To assess the level of 5′-UTR mediated translational regulation in rice, a genome-wide computational analysis of rice 5′-UTRs was carried out in comparison with 5′-UTRs of Arabidopsis. Rice 5′-UTRs were generally longer and more GC-rich than those of Arabidopsis. 30% of rice and 34% of Arabidopsis cDNAs contained upstream AUG triplets (uAUGs). For both organisms, a higher proportion of uAUG-less cDNAs possessed start codons which conformed to the consensus sequence context compared to uAUG-containing cDNAs. Although the GC composition of the start codon context varied between and within rice and Arabidopsis, the critical positions, +4 and −3, were conserved. 24% of rice and 30% of Arabidopsis cDNAs possessed upstream open reading frames (uORFs). Combinatorial analyses of start-codon context, uAUG context and context of uAUGs of upstream open reading frames of individual genes indicate that about 30–34% of genes in rice and Arabidopsis are likely to be influenced at translational level by signals present in 5′-UTR as they possess uAUG/uORFs with sequence context conforming to the consensus sequence There was very little conservation of uAUG positions or uORFs between rice and Arabidopsis. However, there was conservation of uAUG positions between rice, wheat and barley.
Pharbitis [Ipomoea] nil cv. Violet is an excellent model plant for the study of photoperiodic induction of flowering because it can be induced flowering by a single short-day. However there are few molecular-level studies of the induction of flowering in Pharbitis. To gain insight into the photoperiodic induction of flowering, we isolated an APETALA1-like gene (PnAP1), which showed high similarity to SQUAMOSA (SQUA) and AP1. PnAP1 expression at the shoot apex was induced only under flowering-inductive conditions, and PnAP1 expression was induced from 24 h after the start of the inductive dark period. Both night-break and low ambient temperature during the dark period effectively repressed PnAP1 expression and flowering. Timing of PnAP1 expression assessed through induced cotyledon removal indicated that the floral stimulus began to move from cotyledons 14 h after the start of the inductive dark period. The results indicate that floral transitions begin immediately after the inductive dark period and that PnAP1 is a good molecular marker of floral transition.
Up-regulation of the Arabidopsis gene AHL29/SOB3 (At1g76500), encoding a protein with an AT-hook DNA-binding protein motif, is known to function as a suppressor of the phyB phenotype and to cause delayed senescence. We over-expressed the full-length cDNA of AHL29/SOB3 under the cauliflower mosaic virus 35S promoter in Arabidopsis suspension-cultured T87 cells. Preliminary DNA array experiments suggested down-regulation of many genes of the carotenoid synthesis pathway in the transgenic cells. Metabolite analysis with a liquid chromatography-coupled mass spectrometer demonstrated that the accumulation of the carotenoids lycopene, α-carotene, β-carotene, lutein, zeaxanthin, antheraxanthin, violaxanthin and neoxanthin was suppressed in the transgenic cells. These results suggest that up-regulation of AHL29/SOB3 down-regulates the mechanism of carotenoid biosynthesis at the transcriptional level.
The floral meristem identity gene LEAFY (LFY) in Arabidopsis plays a key role in flower development. We isolated two LFY-like genes from radish, designated RsLFY1 and RsLFY2. Comparison of genomic and cDNA sequences revealed that the number and positions of introns are precisely conserved in RsLFY1, RsLFY2 and LFY. Using RsLFY1 full-length cDNA as a probe, genomic DNA blot hybridization analysis detected two hybridizing fragments under high stringency, suggesting that there are two RsLFY loci within radish genome. Both genes were expressed during vegetative growth, reproductive growth, flower development and seed development. RsLFY1 was expressed slightly in leaf primordia and strongly in early floral meristem. It was expressed successively in primordia of sepals, petals, stamens, gynoecium, ovule integument and mature seeds. These results suggest that RsLFY1 plays a similar role to LFY in floral initiation and the developmental stages of floral organs, and that it also may regulate radish seed development, unlike LFY.
From a list of 3087 Arabidopsis putative transcription associated factor (TAF) genes including those possibly involved in transcription processes via their protein interaction, five TAF genes were related to genes upstream of isopentenyl diphosphate biosynthesis, i.e., the mevalonate pathway, by analyzing their network relationships with gene-to-gene Pearson's correlation coefficients calculated from 1388 DNA microarray results. We up-regulated the five candidate genes under the control of a cauliflower mosaic virus 35S promoter in Arabidopsis suspension-cultured T87 cells, and evaluated gene expression in the transgenic cells by DNA microarray analysis. All five of the genes were substantially up-regulated in each transgenic cell line, whereas none of the enzyme genes for the mevalonate pathway exhibited any considerable up-regulation. The inconsistency between the co-expression relationship and lack of consequent up-regulation suggests that it is difficult to find genes controlling isoprenoid upstream metabolites through co-expression analysis. Nevertheless, the results of this study are a basis for further study of isoprenoid synthesis.
Numerous adventitious embryos of Cycas revoluta were successfully induced and grown on the mature zygotic embryos in the well-ripe, naked seeds used on Schenk and Hildebrandt (SH) medium supplemented with 3.0% sucrose, 20% coconut milk, 0.6% agar and the growth regulators of 0.20 to 2.00 mg l−1 BAP and 0.00 to 0.20 mg l−1 2,4-D in combination at pH 5.9 42 to 84 days after the beginning of the culture. Maximum proliferation of 88.7±40.5 adventitious embryos per zygotic embryo was obtained on SH basal medium supplemented with 0.20 mg l−1 BAP and 0.02 mg l−1 2,4-D. Root formation was seen on all of the adventitious embryos by continuous culture on the same medium. Each rooted plantlet was isolated individually and then, grew big enough to juvenile stage that had one to three leaves with pinnate leaflets, thick trunk and primary tap root on SH basal medium without any growth regulator 196 days after the beginning of the culture and was ready for acclimatization.