Genetic transformation of Rangpur lime (Citrus limonia osbeck) with thebO (bacterio-opsin) genen and its initial evaluation forPhytophthora nicotianae resistance

Transgenic plants expressing the bacterio-opsin (bO) gene can spontaneously activate programmed cell death (ped) and may enhance broad-spectrum pathogen resistance by activating an intrinsic defense pathway in plant species such as tobacco and potato. In this work, we produced transgenic Rangpur lime plants with thebO gene, viaAgrobacterium tumefaciens-mediated transformation, and evaluated these plants forPhytophthora nicotianae resistance. Two transgenic lines were successfully regenerated and transformation was confirmed by GUS activity assay, PCR analysis, Southern, Northern and Western blot analyses, in addition to detecting the expressed bO protein by an immunological approach. Evaluation forPhytophthora nicotianae resistance was carried out by plant inoculations with the pathogen and quantification of the affected area. One of the two transgenic lines showed greater tolerance to the fungal pathogen as compared to the control, with significantly smaller stem lesions after pathogen challenge. This increase in pathogen tolerance is correlated with a significantly higher level of transgene expression in this line when compared with the other transgenic line. This is the first report of the introduction of a potentially important gene into Rangpur lime to provide novel pathogen tolerance.     

Accumulation of genes for susceptibility to rust fungi for which barley is nearly a nonhost results in two barley lines with extreme multiple susceptibility

Nonhost resistance is the most common type of resistance in plants. Understanding the factors that make plants susceptible or resistant may help to achieve durably effective resistance in crop plants. Screening of 109 barley (Hordeum vulgare L.) accessions in the seedling stage indicated that barley is a complete nonhost to most of the heterologous rust fungi studied, while it showed an intermediate status with respect to Puccinia triticina, P. hordei-murini, P. hordei-secalini, P. graminis f. sp. lolii and P. coronata ff. spp. avenae and holci. Accessions that were susceptible to a heterologous rust in the seedling stage were much more or completely resistant at adult plant stage. Differential interaction between barley accessions and heterologous rust fungi was found, suggesting the existence of rust-species-specific resistance. In particular, many landrace accessions from Ethiopia and Asia, and naked-seeded accessions, tended to be susceptible to several heterologous rusts, suggesting that some resistance genes in barley are effective against more than one heterologous rust fungal species. Some barley accessions had race-specific resistance against P. hordei-murini. We accumulated genes for susceptibility to P. triticina and P. hordei-murini in two genotypes called SusPtrit and SusPmur, respectively. In the seedling stage, these accessions were as susceptible as the host species to the target rusts. They also showed unusual susceptibility to other heterologous rusts. These two lines are a valuable asset to further experimental work on the genetics of resistance to heterologous rust fungi.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00425-004-1319-1Abbreviations ff. spp Formae speciales - RIL Recombinant inbred line - DC Double cross - DC-S Progeny produced by selfing of double-cross plants     

Constitutively activated barley ROPs modulate epidermal cell size, defense reactions and interactions with fungal leaf pathogens

RHO-like monomeric G-proteins of plants (ROPs, also called RACs), are involved in plant development and interaction with the environment. The barley (Hordeum vulgare) ROP protein HvRACB has been shown to be required for entry of the biotrophic powdery mildew fungus Blumeria graminis f.sp. hordei (Bgh) into living host cells. To get a deeper insight into evolutionarily conserved functions of ROPs in cell polarity and pathogen responses, we stably expressed constitutively activated (CA) mutant variants of different barley ROPs (HvRACB, HvRAC1, HvRAC3) in barley. CA HvROPs induced epidermal cell expansion and/or abolished polarity in tip growing root hairs. All three CA HvROPs enhanced susceptibility of barley to penetration by Bgh whereas only CA HvRAC1 supported whole cell H₂O₂ production in non-penetrated cells. Despite increasing penetration by Bgh, CA HvRAC1 promoted callose deposition at sites of fungal attack and resistance to penetration by Magnaporthe oryzae. The data show an involvement of ROPs in polar growth processes of the monocot barley and in responses to fungal pathogens with different life style.     

Transgenic indica Rice Expressing ns-LTP-Like Protein Shows Enhanced Resistance to Both Fungal and Bacterial Pathogens

Antimicrobial peptides (AMPs) from plant seeds, known to inhibit pathogen growth have a great potential in developing transgenic plants resistant to disease. Some of the nonspecific-lipid transfer proteins (ns-LTP) that facilitate in vitro transport of lipids, show antimicrobial activity in vitro. Rice seeds also contain ns-LTPs; however, these genes are expressed weakly in seedlings. We have transformed Pusa Basmati 1, an elite indica rice cultivar, with the gene for Ace-AMP1 from Allium cepa, coding for an effective antimicrobial protein homologous to ns-LTPs. The gene for Ace-AMP1 was cloned under an inducible rice phenylalanine ammonia-lyase (PAL) or a constitutive maize ubiquitin (UbI) promoter. Ace-AMP1 was expressed in transgenic lines and secreted in the apoplastic space. Protein extracts from leaves of transgenic plants inhibited three major rice pathogens, Magnaporthe grisea, Rhizoctonia solani and Xanthomonas oryzae, in vitro. Enhanced resistance against these pathogens was observed in in planta assays, and the degree of resistance correlating with the levels of Ace-AMP1 with an average increase in resistance to blast, sheath blight, and bacterial leaf blight disease by 86%, 67%, and 82%, respectively. Importantly, transgenic rice plants, with stable integration and expression of Ace-AMP1, retained their agronomic characteristics while displaying enhanced resistance to both fungal and bacterial pathogens.     

Pathogen‐inducible Ta‐Lr34res expression in heterologous barley confers disease resistance without negative pleiotropic effects

Plant diseases are a serious threat to crop production. The informed use of naturally occurring disease resistance in plant breeding can greatly contribute to sustainably reduce yield losses caused by plant pathogens. The Ta‐Lr34res gene encodes an ABC transporter protein and confers partial, durable, and broad spectrum resistance against several fungal pathogens in wheat. Transgenic barley lines expressing Ta‐Lr34res showed enhanced resistance against powdery mildew and leaf rust of barley. While Ta‐Lr34res is only active at adult stage in wheat, Ta‐Lr34res was found to be highly expressed already at the seedling stage in transgenic barley resulting in severe negative effects on growth. Here, we expressed Ta‐Lr34res under the control of the pathogen‐inducible Hv‐Ger4c promoter in barley. Sixteen independent barley transformants showed strong resistance against leaf rust and powdery mildew. Infection assays and growth parameter measurements were performed under standard glasshouse and near‐field conditions using a convertible glasshouse. Two Hv‐Ger4c::Ta‐Lr34res transgenic events were analysed in detail. Plants of one transformation event had similar grain production compared to wild‐type under glasshouse and near‐field conditions. Our results showed that negative effects caused by constitutive high expression of Ta‐Lr34res driven by the endogenous wheat promoter in barley can be eliminated by inducible expression without compromising disease resistance. These data demonstrate that Ta‐Lr34res is agronomically useful in barley. We conclude that the generation of a large number of transformants in different barley cultivars followed by early field testing will allow identifying barley lines suitable for breeding.     

In vitro assay for 2,4-D resistance in transgenic cotton

Summary 2,4-Dichlorophenoxyacetic acid (2,4-D) resistant plants of transgenic cotton (Gossypium hirsutum L.) were produced using Agrobacterium tumefaciens containing a plasmid carrying the neomycin phosphotransferase II (npt II) and 2,4-D monooxygenase (tfd A) genes. An in vitro assay was performed to determine the sensitivity of seed germination, and the growth of seedlings of transgenic and non-transgenic cotton to various concentrations of kanamycin and 2,4-D. The results indicated that kanamycin caused the cotyledons of non-transgenic plants to turn white, but transgenic plants grew normally. Seed germination and seedling growth of non-transgenic plants were strongly inhibited by 2,4-D, but only slightly for transgenic plants. Transgenic plants and non-transgenic plants can be clearly distinguished by the use of 2 mg l⁻¹ 2,4-D in seed germination medium. There was a high correlation between the response of seed germination and the growth of seedlings to kanamycin or 2,4-D, based on the germination ration, albino ratio, dry weight or fresh weight. On this basis, we development a rapid method for identifying transgenic plants that has been verified in the field. These findings will allow identification of cotton transformants at an early stage of plant development, saving time and improving cultivars containing the 2,4-D resistance trait.     

Transgenic mimicry of pathogen attack stimulates growth and secondary metabolite accumulation

Plant secondary metabolites, including pharmaceuticals, flavorings and aromas, are often produced in response to stress. We used chemical inducers of the pathogen defense response (jasmonic acid, salicylate, killed fungi, oligosaccharides and the fungal elicitor protein, cryptogein) to increase metabolite and biomass production in transformed root cultures of the medicinal plant, Withania somnifera, and the weed, Convolvulus sepium. In an effort to genetically mimic the observed effects of cryptogein, we employed Agrobacterium rhizogenes to insert a synthetic gene encoding cryptogein into the roots of C. sepium, W. somnifera and Tylophora tanakae. This genetic transformation was associated with stimulation in both secondary metabolite production and growth in the first two species, and in growth in the third. In whole plants of Convolvulus arvensis and Arabidopsis thaliana, transformation with the cryptogein gene led, respectively, to increases in the calystegines and certain flavonoids. A similar transgenic mimicry of pathogen attack was previously employed to stimulate resistance to the pathogen and abiotic stress. In the present study of biochemical phenotype, we show that transgenic mimicry is correlated with increased secondary metabolite production in transformed root cultures and whole plants. We propose that natural transformation with genes encoding the production of microbial elicitors could influence interactions between plants and other organisms.     

Over-expression of a cacao class I chitinase gene in Theobroma cacao L. enhances resistance against the pathogen, Colletotrichum gloeosporioides

Theobroma cacao L. plants over-expressing a cacao class I chitinase gene (TcChi1) under the control of a modified CaMV-35S promoter were obtained by Agrobacterium-mediated transformation of somatic embryo cotyledons. Southern blot analysis confirmed insertion of the transgene in eight independent lines. High levels of TcChi1 transgene expression in the transgenic lines were confirmed by northern blot analysis. Chitinase activity levels were measured using an in vitro fluorometric assay. The transgene was expressed at varying levels in the different transgenic lines with up to a sixfold increase of endochitinase activity compared to non-transgenic and transgenic control plants. The in vivo antifungal activity of the transgene against the foliar pathogen Colletotrichum gloeosporioides was evaluated using a cacao leaf disk bioassay. The assay demonstrated that the TcChi1 transgenic cacao leaves significantly inhibited the growth of the fungus and the development of leaf necrosis compared to controls when leaves were wound inoculated with 5,000 spores. These results demonstrate for the first time the utility of the cacao transformation system as a tool for gene functional analysis and the potential utility of the cacao chitinase gene for increasing fungal pathogen resistance in cacao.     

High-level secretion of a virally encoded anti-fungal toxin in transgenic tobacco plants

Ustilago maydis killer toxins are small polypeptides (7–14 kDa) whichkill susceptible cells of closely related fungal species. The KP4 toxin is a single polypeptide subunit with a molecular weight of 11.1 kDa. In this work, a transgenic tobacco plant was constructed which secretes the KP4 toxin at a high level. The KP4 toxin expressed in this transgenic plant was of the same size and specificity as the authentic Ustilago KP4 toxin. The expression level was at least 500 times higher than that of the KP6 toxin expressed in plants. Transgenic crop plants producing the KP4 toxin could be rendered resistant to KP4-susceptible fungal pathogens.     

Combined expression of chitinase and lipid transfer protein genes in transgenic carrot plants enhances resistance to foliar fungal pathogens

Two pathogenesis-related (PR) protein genes consisting of a barley chitinase (chi-2) and a wheat lipid-transfer-protein (ltp) were introduced singly and in combination into carrot plants via Agrobacterium-mediated transformation using the phosphinothricin acetyl transferase (bar) gene as a selectable marker. Over 75% of regenerated plants were confirmed to be positive for the transgenes by PCR and RT-PCR and were resistant to the herbicide Liberty (0.2%, v/v). Northern analysis and immunoblotting confirmed the expression of the transgenes in about 70% of the plants, with variable expression levels among individual lines. Southern analysis revealed from one to three copies of each transgene. Transgenic plants were inoculated with two necrotrophic foliar fungal pathogens, Alternaria radicicola and Botrytis cinerea, and showed significantly higher resistance when both PR genes were expressed compared to single-gene transformants. The level of disease reduction in plants expressing both genes was 95% for Botrytis and 90% for Alternaria infection compared to 40–50% for single-gene transformants. The chi2 and ltp genes could be deployed in combination in other crop plants to significantly enhance resistance to necrotrophic fungal pathogens.     

Tissue specificity of the sugarcane bacilliform virus promoter in oat,barley and wheat

The tissue-specificity of the sugarcane bacilliform virus (SCBV) promoter was investigated in oat, barley, and wheat to determine whether its expression pattern in one species was predictive of promoter specificity in the other closely related Gramineae species. Progeny of transgenic plants produced using constructs containing the SCBV promoter driving gusA were sampled at different stages of plant development and stained for GUS activity using a histochemical assay. Overall, the GUS staining patterns were most similar between oat and barley. In all three species, similar GUS staining patterns were observed in mature endosperms, leaves, and floral bracts of developing infloresences. No GUS staining was detected in oat embryos whereas the entire barley embryo was stained, and GUS staining was confined to the scutellum of wheat embryos. Oat and barley stems exhibited GUS staining whereas no GUS staining was observed in stems of the transgenic wheat plants. The SCBV promoter conferred strong GUS staining intensity in most tissues of oat and barley but was generally weaker in wheat. These differences in SCBV promoter specificity indicate that promoter evaluation should be conducted in the target species of interest rather than by extrapolation from expression patterns in other species.     

Overexpression of barley <Emphasis Type="Italic">hva1</Emphasis> gene in creeping bentgrass for improving drought tolerance

The objectives of this study were to test the feasibility of introducing barley hva1 gene, a LEA3 member, into perennial grass species using the Agrobacterium-mediated transformation technique and to determine whether heterologous expression of hva1 would alleviate water-deficit injury in grass species. Creeping bentgrass (Agrostis stolonifera var. palustris), a drought-intolerant grass species, was transformed transiently or stably using three different promoters in conjunction with the downstream report/target genes. Two abscisic acid (ABA)-inducible promoters, ABA1 and ABA2 derived from ABA-response complex (ABRC3) were used to examine stress-responsive expression of the green fluorescent protein (GFP). Transient expression of GFP demonstrated the inducibility of ABA1 and ABA2 promoters in response to exogenous ABA application. The ABA2 promoter was further studied for stress-responsive expression of hva1 and a maize Ubi-1 promoter was tested for constitutive expression of the gene. In the T₀ generation, the Ubi-1::hva1 transformants displayed variable expression levels of HVA1 protein under normal growth conditions. The hva1 gene in the ABA2::hva1 transformants maintained low expression under well-watered conditions, but was upregulated under water-deficit conditions. The tolerance to water deficit of T₀ transgenic lines was assessed by measuring leaf relative water content and visually rating the severity of leaf wilting during to water stress. Under water-stressed conditions, some transgenic lines maintained high water content in leaves and showed significantly less extent of leaf wilting compared with non-transgenic control plants. These results indicated that the introduction of barley hva1 gene using constitutive or stress-inducible promoters lessened water-deficit injury in creeping bentgrass, suggesting that heterologous expression of LEA3 protein genes may enhance the survival ability of creeping bentgrass in water limiting environments.     

Transgenic tobacco and peanut plants expressing a mustard defensin show resistance to fungal pathogens

Defensins are small positively charged, antimicrobial peptides (~5 kDa in size) and some of them exhibit potent antifungal activity. We have cloned the complete cDNA containing an ORF of 243 bp of a defensin of mustard. The deduced amino acid sequence of the peptide showed more than 90% identity to the amino acid sequence of the well-characterized defensins, RsAFP-1 and RsAFP-2 of Raphanus sativus. We have generated and characterized transgenic tobacco and peanut plants constitutively expressing the mustard defensin. Transgenic tobacco plants were resistant to the fungal pathogens, Fusarium moniliforme and Phytophthora parasitica pv. nicotianae. Transgenic peanut plants showed enhanced resistance against the pathogens, Pheaoisariopsis personata and Cercospora arachidicola, which jointly cause serious late leaf spot disease. These observations indicate that the mustard defensin gene can be deployed for deriving fungal disease resistance in transgenic crops.     

The Sweet Pepper Ferredoxin-Like Protein (pflp) Conferred Resistance Against Soft Rot Disease in Oncidium Orchid

Genetic engineering to date has not been used to introduce disease resistance genes into the orchid gene pool. The ferredoxin-like protein gene originally isolated from sweet pepper is thought to function as a natural defense against infection due to its antimicrobial properties. Hence it was reasoned that introduction of this gene might produce Oncidium plants resistant to Erwinia carotovora, the causal agent for the soft rot disease. An expression vector containing sweet pepper ferredoxin-like protein (pflp) cDNA, hph and gusA coding sequence was successfully transformed into protocorm-like bodies (PLBs) of Oncidium orchid, using Agrobacterium tumefaciens strain EHA105. A total of 17 independent transgenic orchid lines was obtained, out of which six transgenic lines (-glucuronidase (GUS) positive) were randomly selected and confirmed by Southern, northern and western blot analyses. A bioassay was conducted on the transgenic lines. Transgenic plants showed enhanced resistance to E. carotovora, even when the entire plant was challenged with the pathogen. Our results suggest that pflp may be an extremely useful gene for genetic engineering strategies in orchids to confer resistance against soft rot disease.     

Production of transgenic potato exhibiting enhanced resistance to fungal infections and herbicide applications

Potato (Solanum tuberosum L.), one of the most important food crops, is susceptible to a number of devastating fungal pathogens in addition to bacterial and other pathogens. Producing disease-resistant cultivars has been an effective and useful strategy to combat the attack of pathogens. Potato was transformed with Agrobacterium tumefaciens strain EHA101 harboring chitinase, (ChiC) isolated from Streptomyces griseus strain HUT 6037 and bialaphos resistance (bar) genes in a binary plasmid vector, pEKH1. Polymerase chain reaction (PCR) analysis revealed that the ChiC and bar genes are integrated into the genome of transgenic plants. Different insertion sites of the transgenes (one to six sites for ChiC and three to seven for bar) were indicated by Southern blot analysis of genomic DNA from the transgenic plants. Expression of the ChiC gene at the messenger RNA (mRNA) level was confirmed by Northern blot analysis and that of the bar gene by herbicide resistance assay. The results obviously confirmed that the ChiC and bar genes are successfully integrated and expressed into the genome, resulting in the production of bialaphos-resistant transgenic plants. Disease-resistance assay of the in vitro and greenhouse-grown transgenic plants demonstrated enhanced resistance against the fungal pathogen Alternaria solani (causal agent of early blight).     

The Saccharomyces cerevisiae chitinase,encoded by the CTS1-2 gene,confers antifungal activity against Botrytis cinerea to Transgenic tobacco

The Saccharomyces cerevisiae chitinase, encoded by the CTS1-2 gene has recently been confirmed by in vitro tests to possess antifungal abilities. In this study, the CTS1-2 gene has been evaluated for its in planta antifungal activity by constitutive overexpression in tobacco plants to assess its potential to increase the plant's defence against fungal pathogens. Transgenic tobacco plants, generated by Agrobacterium-mediated transformation, showed stable integration and inheritance of the transgene. Northern blot analyses conducted on the transgenic tobacco plants confirmed transgene expression. Leaf extracts from the transgenic lines inhibited Botrytis cinerea spore germination and hyphal growth by up to 70% in a quantitative in vitro assay, leading to severe physical damage on the hyphae. Several of the F₁ progeny lines were challenged with the fungal pathogen, B. cinerea, in a detached leaf infection assay, showing a decrease in susceptibility ranging from 50 to 70%. The plant lines that showed increased disease tolerance were also shown to have higher chitinase activities.     

Transgenic tobacco plants which express thechiA gene fromSerratia marcescens have enhanced tolerance toRhizoctonia solani

We have prepared independent lines of transgenic tobacco plants which express high levels of theSerratia marcescens ChiA protein intracellulary or extracellularly (in glycosylated or unglycosylated forms). We have measured the susceptibility, of these plants toRhizoctonia solani infection in greenhouse trials and in the field. Transgenic tobacco plants which constitutively express theS. marcescens ChiA protein exhibit tolerance to the fungal pathogenR. solani. Disease tolerance is observed in transgenic tobacco plants which express the bacterial chitinase intra-or extracellulary. This is the first report to document disease reduction in the field in transgenic plants engineered for fungal disease tolerance.     

Transgenic Tobacco Plants Constitutively Overexpressing a Rice Thaumatin-like Protein (PR-5) Show Enhanced Resistance to Alternaria alternata

Overexpression of antifungal pathogenesis-related (PR) proteins in crop plants has the potential for enhancing resistance against fungal pathogens. Thaumatin-like proteins (TLPs) are one group (PR-5, permatins) of antifungal PR-proteins isolated from various plants. In the present study, a plasmid containing a cDNA of rice tlp (D34) under the control of the CaMV-35S promoter was introduced into tobacco plants through Agrobacterium-mediated transformation system. A considerable overproduction of TLP was observed in transformed tobacco plants by Western blot analysis. There was a large accumulation of tlp mRNA in transgenic plants as revealed by Northern blot analysis. Southern blot analysis of the DNA from transgenic tobacco plants confirmed the presence of the rice tlp gene in the genomic DNA of transgenic tobacco plants. Immunoblot analysis of intracellular and extracellular proteins of transgenic tobacco leaves using a Pinto bean TLP antibody demonstrated that the 23-kDa TLP was secreted into the extracellular matrix. T₂ progeny of regenerated plants transformed with TLP gene were tested for their disease reaction to Alternaria alternata, the brown spot pathogen. Transgenic tobacco plants expressing TLP at high levels showed enhanced tolerance to necrotization caused by the pathogen. This revised version was published online in July 2006 with corrections to the Cover Date.     

Constitutive expression of two endochitinases from root nodules ofElaeagnus umbellata confers resistance on transgenicArabidopsis plants against the fungal pathogenBotrytis cinerea

Plant chitinases have been known as pathogenesis-related (PR) proteins, but recent studies suggest that they play functional roles during normal plant growth and development. We previously isolated two cDNA clones encoding endochitinases,EuNOD-CHT1 and -CHT2, from the root nodules ofElaeagnus umbellata. These genes show differential expression patterns, with theEuNOD-CHT1 gene being active in the root nodules and meristems, whileEuNOD-CHT2 is preferentially expressed in the infected cells of those nodules. To elucidate the functional roles of these two endochitinases, we have now constitutively expressed each gene in a heterologous plant system,Arabidopsis thaliana. Stable inheritance and expression of the transgenes were confirmed by genomic Southern hybridization and RT-PCR. Our transgenic plants did not differ morphologically from the wild types. However, constitutive expression ofEuNOD-CHT1 and -CHT2 inArabidopsis resulted in increased resistance against a fungal pathogen,Botrytis cinerea, but not against a bacterial agent,Pseudomonas syringae pv. Tomato DC3000. Expression levels were enhanced by both wounding and jasmonic acid treatments (forEuNOD-CHT1), or by jasmonic acid only (forEuNOD-CHT2). These data suggest thatEuNOD-CHT1 and -CHT2 primarily play defensive roles during root nodule development inE. umbellata.     

Photoregulation of germination in seed of transgenic lines of tobacco and Arabidopsis which express an introduced cDNA encoding phytochrome A or phytochrome B

Photoinduction and photoinhibition of germination in seed from a homozygous tobacco (Nicotiana tabacum L.) line containing an introduced oat phyA cDNA (encoding phytochrome A) is compared with that of isogenic wild-type (WT) tobacco. Under continuous irradiation by a light source with a low redfar-red (RFR) ratio the transgenic tobacco seed appeared to be less susceptible to photoinhibition of germination compared with WT seed. However, induction of germination following a short pulse by R (666 nm) was not enhanced in the genotype transformed by oat phyA cDNA compared with the WT; neither did germination of the transgenic tobacco seed show an increased sensitivity to saturating pulses of light of longer wavelengths (666–730 nm). In seeds of transgenic Arabidopsis thaliana (L.) Heynh. which contained an introduced phytochrome-B-encoding cDNA, levels of dark germination were enhanced, consistent with mediation of response by phytochrome B-P_fr. The germination behaviour of Arabidopsis genotypes wich contained an introduced cDNA encoding phytochrome A, however, did not significantly differ from that of the WT.Abbreviations ABO seed transformed with Arabidopsis phyB - cDNA; CaMV cauliflower mosaic virus - FR far-red light - P_fr far-red-absorbing form of phytochrome - P_tot total phytochrome - P_fr/P_tot phytochrome photoequilibrium - R red light - RBO seed transformed with rice phyB cDNA - RFR quantum ratio of red and far-red light - WL white light - WL + FR whitelight supplemented with far-red light - WT wild type The authors wish to thank R.D. Vierstra (Department of Horticulture, University of Wisconsin-Madison, USA) for providing the transgenic tobacco line, and M.T. Boylan, D. Wagner and P.H. Quail (U.C. Berkeley/USDA Plant Gene Expression Center, Albany, Calif. USA) for providing the transgenic Arabidopsis lines. The work presented in this paper was funded by grants from the Agricultural and Food Research Council (H.S., A.C.M., G.C.W.).