Plasticity and environment-specific covariances: an investigation of floral-vegetative and within flower correlations

Floral traits are commonly thought to be more canalized than vegetative ones. In addition, floral and vegetative traits are hypothesized to be genetically decoupled, enabling vegetative structures to respond plastically to environmental heterogeneity, and to evolve in response to selection without disrupting the reproductive function of flowers. To test these hypotheses, we evaluate the genetic architecture of floral and vegetative traits in natural populations of Arabidopsis thaliana raised under variable light-quality environments. Plants were grown either under high or low ratios of red to far-red (R:FR) light, an aspect of light quality that varies with neighbor proximity and regulates competitive shade-avoidance responses. Across environments, we detected significant genetic variation for the average expression of all measured floral traits (petal length and width, stamen length, pistil length, stigma-anther separation, and exsertion of both the stamen and pistil beyond the corolla). Light quality significantly influenced the absolute size of several floral traits as well as the allometry (i.e., relative scaling) of all floral traits, and genotypes differed in the plasticity of floral traits to the light treatments. Exposure to low relative to high R:FR resulted in significantly greater elongation in the vegetative trait, petiole length, and genotypes again differed in the plasticity of this trait to R:FR. Consistent with prior studies, most floral traits were less plastic than the vegetative trait; herkogamy (i.e., stigma-anther separation) was the exception and expressed more variable trait values across environments than petiole length, apparently as a consequence of the independent responses of stamens and pistils. Flowers also showed strong phenotypic integration; genotypic correlations were significantly positive among floral traits within each light treatment. Although floral-vegetative correlations were not significant in the high R:FR light treatment, significant correlations were detected between petal traits, pistil length, and petiole length under low R:FR, in contrast to the widely held hypothesis that floral and vegetative traits are genetically independent. Finally, we detected selection for reduced herkogamy in the low R:FR light treatment. The observed correlation between functional trait groups suggest that vegetative plasticity may affect the expression of floral traits in some environments, and that environment-specific constraints may exist on the evolution of floral and vegetative traits.     

Selected Components of the Shade-Avoidance Syndrome Are Displayed in a Normal Manner in Mutants of Arabidopsis thaliana and Brassica rapa Deficient in Phytochrome B

Several growth parameters associated with the phytochrome-mediated shade avoidance syndrome have been measured in seedlings and mature plants of a wild-type and a hy3 mutant of Arabidopsis thaliana deficient in phytochrome B. Growth parameters were compared in plants grown in either white light (high red:far-red [R:FR] ratio) or white light plus added far-red (FR) light (low R:FR ratio). Wild-type Arabidopsis exhibited increased hypocotyl and petiole extension under a low, compared with a high, R:FR ratio. The hy3 mutant did not respond to low R:FR ratio by increase in hypocotyl or petiole length. Extension growth of wild-type plants was stimulated by brief end-of-day FR pulses, but similar treatment had no effect on extension growth of hy3 mutant plants. However, some responses to low R:FR ratio seen in the wild-type plants were also evident in the hy3 mutants. The number of days to bolting, the developmental stage at bolting, the leaf area, and the specific stem weight (weight per unit of length) all decreased in the wild-type and hy3 seedlings in response to low R:FR ratio. Low R:FR ratio caused a larger decrease in leaf area and specific stem weight in the mutant seedlings than in wild-type seedlings. The effects of low R:FR ratio on leaf area and specific stem weight were opposite to those of the hy3 lesion, which resulted in increased leaf area and specific stem weight in comparison with the wild type. Both leaf area and specific stem weight responses to low R:FR ratio also were unchanged in the ein mutant of Brassica rapa, known to be deficient in phytochrome B. These responses represent components of the shade-avoidance syndrome, and, consequently, the results indicate that phytochrome B cannot be solely responsible for the perception of R:FR ratio and the induction of shade-avoidance responses. The hypothesis is proposed that different phytochromes may be responsible for the regulation of extension growth and the regulation of lateral or radial expansion.     

Flowering responses to altered expression of phytochrome in mutants and transgenic lines of Arabidopsis thaliana (L.) Heynh.

The long-day plant Arabidopsis thaliana (L.) Heynh. flowers early in response to brief end-of-day (EOD) exposures to far-red light (FR) following a fluorescent short day of 8 h. FR promotion of flowering was nullified by subsequent brief red light (R) EOD exposure, indicating phytochrome involvement. The EOD response to R or FR is a robust measure of phytochrome action. Along with their wild-type (WT) parents, mutants deficient in either phytochrome A or B responded similarly to the EOD treatments. Thus, neither phytochrome A nor B exclusively regulated flowering, although phytochrome B controlled hypocotyl elongation. Perhaps a third phytochrome species is important for the EOD responses of the mutants and/or their flowering is regulated by the amount of the FR-absorbing form of phytochrome, irrespective of the phytochrome species. Overexpression of phytochrome A or phytochrome B resulted in differing photoperiod and EOD responses among the genotypes. The day-neutral overexpressor of phytochrome A had an EOD response similar to all of the mutants and WTs, whereas R EOD exposure promoted flowering in the overexpressor of phytochrome B and FR EOD exposure inhibited this promotion. The comparisons between relative flowering times and leaf numbers at flowering of the over-expressors and their WTs were not consistent across photoperiods and light treatments, although both phytochromes A and B contributed to regulating flowering of the transgenic plants.     

Phytochrome B and at Least One Other Phytochrome Mediate the Accelerated Flowering Response of Arabidopsis thaliana L. to Low Red/Far-Red Ratio

We have investigated the involvement of phytochrome B in the early-flowering response of Arabidopsis thaliana L. seedlings to low red:far-red (R/FR) ratio light conditions. The phytochrome B-deficient hy3 (phyB) mutant is early flowering, and in this regard it resembles the shade-avoidance phenotype of its isogenic wild type. Seedlings carrying the hy2 mutation, resulting in a deficiency of phytochrome chromophore and hence of active phytochromes, also flower earlier than wild-type plants. Whereas hy3 or hy2 seedlings show only a slight acceleration of flowering in response to low R/FR ratio, seedlings that are doubly homozygous for both mutations flower earlier than seedlings carrying either phytochrome-related mutation alone. This additive effect clearly indicates the involvement of one or more phytochrome species in addition to phytochrome B in the flowering response as well as indicating the presence of some functional phytochrome B in hy2 seedlings. Seedlings that are homozygous for the hy3 mutation and one of the fca, fwa, or co late-flowering mutations display a pronounced early-flowering response to low R/FR ratio. A similar response to low R/FR ratio is displayed by seedlings doubly homozygous for the hy2 mutation and any one of the late-flowering mutations. Thus, placing the hy3 or hy2 mutations into a late-flowering background has the effect of uncovering a flowering response to low R/FR ratio. Seedlings that are triply homozygous for the hy3, hy2 mutations and a late-flowering mutation flower earlier than the double mutants and do not respond to low R/FR ratio. Thus, the observed flowering responses to low R/FR ratio in phytochrome B-deficient mutants can be attributed to the action of at least one other phytochrome species.     

Phytochrome A is an irradiance-dependent red light sensor

Plants perceive red (R) and far-red (FR) light signals using the phytochrome family of photoreceptors. In Arabidopsis thaliana, five phytochromes (phyA-phyE) have been identified and characterized. Unlike other family members, phyA is subject to rapid light-induced proteolytic degradation and so accumulates to relatively high levels in dark-grown seedlings. The insensitivity of phyA mutant seedlings to prolonged FR and wild-type appearance in R has led to suggestions that phyA functions predominantly as an FR sensor during the early stages of seedling establishment. The majority of published photomorphogenesis experiments have, however, used <50 micromol m(-2) sec(-1) of R when characterizing phytochrome functions. Here we reveal considerable phyA activity in R at higher (>160 micromol m(-2) sec(-1)) photon irradiances. Under these conditions, plant architecture was observed to be largely regulated by the redundant actions of phytochromes A, B and D. Moreover, quadruple phyBphyCphyDphyE mutants containing only functional phyA displayed R-mediated de-etiolation and survived to flowering. The enhanced activity of phyA in continuous R (Rc) of high photon irradiance correlates with retarded degradation of the endogenous protein in wild-type plants and prolonged epifluorescence of nuclear-localized phyA:YFP in transgenic lines. Such observations suggest irradiance-dependent 'photoprotection' of nuclear phyA in R, providing a possible explanation for the increased activity observed. The discovery that phyA can function as an effective irradiance sensor, even in light environments that establish a high Pfr concentration, raises the possibility that phyA may contribute significantly to the regulation of growth and development in daylight-grown plants.     

Different Roles for Phytochrome in Etiolated and Green Plants Deduced from Characterization of Arabidopsis thaliana Mutants

We have isolated a new complementation group of Arabidopsis thaliana long hypocotyl mutant (hy6) and have characterized a variety of light-regulated phenomena in hy6 and other previously isolated A. thaliana hy mutants. Among six complementation groups that define the HY phenotype in A. thaliana, three (hy1, hy2, and hy6) had significantly lowered levels of photoreversibly detectable phytochrome, although near wild-type levels of the phytochrome apoprotein were present in all three mutants. When photoregulation of chlorophyll a/b binding protein (cab) gene expression was examined, results obtained depended dramatically on the light regime employed. Using the red/far-red photoreversibility assay on etiolated plants, the accumulation of cab mRNAs was considerably less in the phytochrome-deficient mutants than in wild-type A. thaliana seedlings. When grown in high-fluence rate white light, however, the mutants accumulated wild-type levels of cab mRNAs and other mRNAs thought to be regulated by phytochrome. An examination of the light-grown phenotypes of the phytochrome-deficient mutants, using biochemical, molecular, and morphological techniques, revealed that the mutants displayed incomplete chloroplast and leaf development under conditions where wild-type chloroplasts developed normally. Thus, although phytochrome may play a role in gene expression in etiolated plants, a primary role for phytochrome in green plants is likely to be in modulating the amount of chloroplast development, rather than triggering the initiation of events (e.g., gene expression) associated with chloroplast development.     

The Arabidopsis ELF3 gene regulates vegetative photomorphogenesis and the photoperiodic induction of flowering

Flowering in Arabidopsis thaliana is promoted by long-day (LD) photoperiods such that plants grown in LD flower earlier, and after the production of fewer leaves, than plants grown in short-day (SD) photoperiods. The early-flowering 3 ( elf 3) mutant of Arabidopsis , which is insensitive to photoperiod with regard to floral initiation has been characterized. elf 3 mutants are also altered in several aspects of vegetative photomorphogenesis, including hypocotyl elongation. When inhibition of hypocotyl elongation was measured, elf 3 mutant seedlings were less responsive than wild-type to all wavelengths of light, and most notably defective in blue and green light-mediated inhibition. When analyzed for the flowering-time phenotype, elf 3 was epistatic to mutant alleles of the blue-light receptor encoding gene, HY 4. However, when elf 3 mutants were made deficient for functional phytochrome by the introduction of hy 2 mutant alleles, the elf 3 hy 2 double mutants displayed the novel phenotype of flowering earlier than either single mutant while still exhibiting photoperiod insensitivity, indicating that a phytochrome-mediated pathway regulating floral initiation remains functional in elf 3 single mutants. In addition, the inflorescences of one allelic combination of elf 3 hy 2 double mutants form a terminal flower similar to the structure produced by tfl 1 single mutants. These results suggest that one of the signal transduction pathways controlling photoperiodism in Arabidopsis is regulated, at least in part, by photoreceptors other than phytochrome, and that the activity of the Arabidopsis inflorescence and floral meristem identity genes may be regulated by this same pathway.     

FRL1 is required for petal and sepal development in Arabidopsis

A novel flower mutant, frl1 (frill 1) was isolated in Arabidopsis thaliana. The frl1 mutant has serrated petals and sepals but the other floral and vegetative organs appear to be normal. To analyse the role of the FRL1 gene, morphological, cytological and double mutant analyses were carried out. The frl1 flower had broader petals and sepals as compared with the wild-type. The distal region of frl1 petals contained fewer epidermal cells but their size was variable and generally larger than that in the wild-type. However, no significant difference was found in the basal region. Observations of the early petal development revealed that the morphology of the developing frl1 petal was normal until the middle of stage 9, but the frl1 phenotype became apparent in stages later than 10. Furthermore, larger nuclei with varied sizes were observed in the distal region of frl1 petals, but not in this region in wild-type petals. This strongly suggests that abnormal endo-reduplication had occurred. These observations indicate that the frl1 mutation affects the number of cell divisions and the subsequent cell expansion during the late stage of petal lamina formation, and that FRL1 might be maintaining the mitotic state or suppressing the transition to the endo-reduplication cycle. Double mutants with the homeotic mutants apetala3-1 and agamous showed additive phenotypes. Ectopic petals in the third whorl of fr11 ag flowers were serrated, indicating that the FRL1 gene acts in petal and sepal development in an organ-specific manner.     

The ASK1 gene regulates development and interacts with the UFO gene to control floral organ identity in Arabidopsis.

Normal flower development likely requires both specific and general regulators. We have isolated an Arabidopsis mutant ask1-1 (for -Arabidopsis skp1-like1-1), which exhibits defects in both vegetative and reproductive development. In the ask1-1mutant, rosette leaf growth is reduced, resulting in smaller than normal rosette leaves, and internodes in the floral stem are shorter than normal. Examination of cell sizes in these organs indicates that cell expansion is normal in the mutant, but cell number is reduced. In the mutant, the numbers of petals and stamens are reduced, and many flowers have one or more petals with a reduced size. In addition, all mutant flowers have short stamen filaments. Furthermore, petal/stamen chimeric organs are found in many flowers. These results indicate that the ASK1 gene affects the size of vegetative and floral organs. The ask1 floral phenotype resembles somewhat that of the Arabidopsis ufo mutants in that both genes affect whorls 2 and 3. We therefore tested for possible interactions between ASK1 and UFO by analyzing the phenotypes of ufo-2 ask1-1 double mutant plants. In these plants, vegetative development is similar to that of the ask1-1 single mutant, whereas the floral defects are more severe than those in either single mutant. Interior to the first whorl, the double mutant flowers have more sepals or sepal-like organs than are found in ufo-2, and less petals than ask1-1. Our results suggest that ASK1 interacts with UFO to control floral organ identity in whorls 2 and 3. This is very intriguing because ASK1 is very similar in sequence to the yeast SKP1 protein and UFO contains an F-box, a motif known to interact with SKP1 in yeast. Although the precise mechanism of ASK1 and UFO action is unknown, our results support the hypothesis that these two proteins physically interact in vivo.     

Induced mutations affecting pollinator choice in Mimulus lewisii (Phrymaceae)

The flowering plants are one of the most phenotypically varied and wide-ranging groups of organisms on earth, and yet, we have limited understanding of the contribution of animal pollinators to the diversification of floral form. To explore the interaction between variation in floral form and pollinator behavior, we observed the foraging behavior of bumblebees (Bombus impatiens) when presented with both wild-type Mimulus lewisii plants and each of three chemically induced single-locus mutants with altered floral phenotypes, including loss of the three lower petals, loss of nectar guides, and a change in petal color patterning. We found that each of the mutants attracted successful pollinator visits at just 29–80% of the rate relative to wild-type flowers, suggesting that effective recruitment of bumblebee pollinators requires the landing platform provided by the lower petals, and visual cues provided by the nectar guides and petal color pattern. Since single-locus recessive mutations are capable of ablating the lower petals, nectar guides, and color pattern, such changes in floral form provide insight into the driving forces behind plant adaptation.     

The rosette habit of Arabidopsis thaliana is dependent upon phytochrome action: novel phytochromes control internode elongation and flowering time

A major function of phytochromes in light-grown plants involves the perception of changes in the relative amounts of red and far-red light (R:FR ratio) and the initiation of the shade-avoidance response. In Arabidopsis thaliana, this response is typified by increased elongation growth of petioles and accelerated flowering and can be fully induced by end-of-day far-red light (EOD FR) treatments. Phytochrome B-deficient (phyB) mutants, which have a constitutive elongated-petiole and early-flowering phenotype, do not display a petiole elongation growth response to EOD FR, but they do respond to EOD FR by earlier flowering. Seedlings deficient in both phytochrome A and phytochrome B (phyA phyB), have a greatly reduced stature compared with wild-type or either monogenic mutant. The phyA phyB double null mutants also respond to EOD FR treatments by flowering early, suggesting the operation of novel phytochromes. Contrary to the behaviour of wild-type or monogenic phyA or phyB seedlings, petiole elongation in phyA phyB seedlings is reduced in response to EOD FR treatments. This reduction in petiole elongation is accompanied by the appearance of elongated internodes such that under these conditions the plants no longer display a rosette habit.     

Photoresponses of Light-Grown phyA Mutants of Arabidopsis (Phytochrome A Is Required for the Perception of Daylength Extensions)

Several aspects of the photophysiology of wild-type Arabidopsis thaliana seedlings were compared with those of a phytochrome A null mutant, phyA-1, and a mutant, fhy1, that is putatively involved in the transduction of light signals from phytochrome A. Although phyA seedlings display a near wild-type phenotype when grown in white light (W), they nevertheless display several photomorphogenic abnormalities. Thus, whereas the germination of wild-type and fhy1 seeds is almost fully promoted by a pulse of red light (R) or by continuous far-red light (FR), phyA seed germination is responsive only to R. Following growth under day/night cycles, but not under continuous W, the hypocotyls of light-grown phyA and fhy1 seedlings are more elongated than those of wild-type seedlings. For seedlings grown under low red/far-red (R/FR) ratio light conditions, phyA and fhy1 seedlings display a more marked promotion of hypocotyl elongation than wild-type seedlings. Similarly, seedlings that are doubly null for phytochrome A and phytochrome B(phyA phyB) also have more elongated hypocotyls under low R/FR ratio conditions than phyB seedlings. This indicates that phytochrome A action in light-grown seedlings is antagonistic to the action of phytochrome B. Although wild-type, fhy1, and phyA seedlings flower at essentially the same time under both short-day and long-day conditions, an obvious consequence of phytochrome A deficiency is a pronounced late flowering under conditions where a short day of 8 h of fluorescent W is extended by 8 h of low-fluence-rate incandescent light. The evidence thus indicates that phytochrome A plays a role in seed germination, in the control of elongation growth of light-grown seedlings, and in the perception of daylength.     

Isolation and characterization of a Brassica napus cDNA corresponding to a B-class floral development gene

B-class floral homeotic genes are required for the proper formation and identity of petals and stamens in dicot flowers. A partial cDNA clone encoding a B-class gene, BnAP3 (Brassica napus APETALA3), was isolated from a B. napus cDNA library derived from young inflorescence meristems. The 5' region of the cDNA was retrieved by RACE. The deduced amino acid sequence of the full-length clone exhibited high similarity to APETALA3 of Arabidopsis thaliana and functionally homologous proteins from other species. 5' RACE and Southern analysis suggests that BnAP3 has multiple alleles in B. napus. Expression analysis assayed by RT-PCR shows that BnAP3 is expressed in floral tissues, as well as non-floral tissues such as root and bract. Transformation of wild-type A. thaliana and B. napus plants with BnAP3 under the control of a promoter specific to reproductive organs converts carpels to stamens, while the expression of this construct in A. thaliana plants mutant for AP3 restores the development of third-whorl stamens in addition to directing a carpel to stamen conversion in the fourth whorl.     

Far-red light-insensitive, phytochrome A-deficient mutants of tomato

We have selected two recessive mutants of tomato with slightly longer hypocotyls than the wild type, one under low fluence rate (3 mol/m²/s) red light (R) and the other under low fluence rate blue light. These two mutants were shown to be allelic and further analysis revealed that hypocotyl growth was totally insensitive to far-red light (FR). We propose the gene symbol fri (far-red light insensitive) for this locus and have mapped it on chromosome 10. Immunochemically detectable phytochrome A polypeptide is essentially absent in the fri mutants as is the bulk spectrophotometrically detectable labile phytochrome pool in etiolated seedlings. A phytochrome B-like polypeptide is present in normal amounts and a small stable phytochrome pool can be readily detected by spectrophotometry in the fri mutants. Inhibition of hypocotyl growth by a R pulse given every 4 h is quantitatively similar in the fri mutants and wild type and the effect is to a large extent reversible if R pulses are followed immediately by a FR pulse. After 7 days in darkness, both fri mutants and the wild type become green on transfer to white light, but after 7 days in FR, the wild-type seedlings that have expanded their cotyledons lose their capacity to green in white light, while the fri mutants de-etiolate. Adult plants of the fri mutants show retarded growth and are prone to wilting, but exhibit a normal elongation response to FR given at the end of the daily photoperiod. The inhibition of seed germination by continuous FR exhibited by the wild type is normal in the fri mutants. It is proposed that these fri mutants are putative phytochrome A mutants which have normal pools of other phytochromes.     

Far-red light reflected from neighbouring vegetation promotes shoot elongation and accelerates flowering in spring barley plants

Field experiments were conducted in St Paul, MN, USA, to test the hypothesis that early season declines in the red:far-red ratio (R:FR) associated with FR reflection from neighbouring leaves have a role in regulating barley development. Treatment plants were grown adjacent to densely sown border rows of barley. The borders functioned to reflect far-red (FR), which reduced R:FR within the treatment plant light environment without shading treatment plants. Barriers were set in the soil to minimize root interactions between treatment plants and borders. Treatment plants were spaced either 2 or 16 cm apart. The presence of borders significantly increased shoot leaf and internode lengths at both plant spacings. Leaf sheath length data suggest that interactions between 2 cm spaced treatment plants enhanced plant responsiveness to the presence of borders. Border treatments shortened the period of vegetative growth prior to initiation of main shoot floral primordia. Bordered plants formed fewer main shoot leaves, initiated internode elongation at a lower node, and had slightly earlier heading dates than unbordered controls. Leaf appearance rate was not influenced by border treatments. We conclude that barley shoot development is photomorphogenically modulated by R:FR. Early season shifts in R:FR could have a significant influence on shoot development given that barley has the capacity to detect and developmentally respond to declines in R:FR associated with FR reflection from neighbours.     

The major volatile organic compound emitted from Arabidopsis thaliana flowers, the sesquiterpene (E)-β-caryophyllene, is a defense against a bacterial pathogen

Flowers have a high risk of pathogen attack because of their rich nutrient and moisture content, and high frequency of insect visitors. We investigated the role of (E)-β-caryophyllene in floral defense against a microbial pathogen. This sesquiterpene is a common volatile compound emitted from flowers, and is a major volatile released from the stigma of Arabidopsis thaliana flowers. Arabidopsis thaliana lines lacking a functional (E)-β-caryophyllene synthase or constitutively overexpressing this gene were challenged with Pseudomonas syringae pv. tomato DC3000, which is a bacterial pathogen of brassicaceous plants. Flowers of plant lines lacking (E)-β-caryophyllene emission showed greater bacterial growth on their stigmas than did wild-type flowers, and their seeds were lighter and misshapen. By contrast, plant lines with ectopic (E)-β-caryophyllene emission from vegetative parts were more resistant than wild-type plants to pathogen infection of leaves, and showed reduced cell damage and higher seed production. Based on in vitro experiments, (E)-β-caryophyllene seems to act by direct inhibition of bacterial growth, rather than by triggering defense signaling pathways. (E)-β-Caryophyllene thus appears to serve as a defense against pathogens that invade floral tissues and, like other floral volatiles, may play multiple roles in defense and pollinator attraction.     

The Evergreen gene is essential for flower initiation in carnation

One of the leading cut-flower crops in the world, the greenhouse carnation (Dianthus caryophyllus), has been subjected to intense breeding efforts for the past few hundred years. As an ornamental crop, flowering and flower architecture are major breeding targets that are constantly in demand. In an ongoing breeding program aimed at improving these characteristics, two mutants heterozygous for a mutation in a gene termed evergreen (e) were identified. In these mutants, spike-like clusters of bracteoles subtend each flower. Genetic analysis of the mutants confirmed the semidominant nature of this nuclear mutation and that the two original mutants were allelic at the evergreen locus. In homozygous mutant plants, a more severe phenotype was observed. Flower formation was completely blocked and spikelike clusters of bracteoles did not subtend any flowers. Morphological characterization of mutant plants revealed that vegetative growth and inflorescence structure are not affected by the mutant allele. In plants heterozygous for the evergreen mutation, fertility, petal and pistil length, calyx diameter, and stamen number were not affected. However, flowers from these heterozygous plants had a reduced number of petals, suggesting an intriguing link between evergreen and the double flower (d) gene that determines petal number in carnation. The control by evergreen of bracteole formation, floral meristem initiation, and petal number in carnation is discussed in comparison to the recessive leafy (lfy) and floricaula (flo) mutants of Arabidopsis and Antirrhinum, respectively.     

大白菜BrMYB34-3基因的3′-RACE克隆及表达

以大白菜叶片为材料,根据NCBI数据库中Br MYB34-3基因序列的已知信息,利用3-RACE获得了Br MYB34-3基因全长,用RT-PCR方法对Br MYB34-3在不同组织中的表达进行分析.结果显示,该基因全长1 135 bp,编码280个氨基酸.Br MYB34-3具有R2R3-MYB(含有2个MYB结构域的转录因子)典型的R2、R3结构域及基序.其氨基酸序列与大白菜的Br MYB34-1和Br MYB34-2、拟南芥的At MYB34具有较高的一致性.Br MYB34-3在莲座叶、当天开的花中表达水平较高,在花序顶端表达水平较低,在根和花序轴中未检测到表达,这与拟南芥At MYB34的表达模式不同.研究表明,Br MYB34-3是大白菜中的MYB34同源基因,在功能上可能与拟南芥At MYB34基因存在差异.     

Nicotiana plumbaginifolia hlg mutants have a mutation in a PHYB-type phytochrome gene: they have elongated hypocotyls in red light, but are not elongated as adult plants

Two new allelic mutants of Nicotiana plumbaginifolia have been isolated which display a hypocotyl which is long (hlg) when seedlings are grown in continuous white light (W). This can be accounted for by the decreased response to red light (R) of the hypocotyl elongation rate in these mutants. Responses to other wavelengths are unaffected in the mutants. When grown in white light, mature hlg mutants are not elongated with respect to the wild-type; they also bolt and flower later. The shade-avoidance responses to red/far red ratio (R:FR) are intact in these mutants. Both mutants are deficient in a phyB-like polypeptide that is immunodetectable in the wild-type; both have wild-type levels of a phyA-like polypeptide. These alleles are inherited in a partially dominant manner, and correspond to single-base missense mutations in a gene highly homologous to N. tabacum PHYB, which codes for a phytochrome B-type photoreceptor. One allele, hlg-1, has an introduced amino acid substitution; this may define a residue essential for phytochrome protein stability. The other allele, hlg-2, has a stop codon introduced C-terminal to the chromophore binding domain. As these phyB mutants are unaffected in shade-avoidance responses, but deficient in perception of R, it is concluded that the phyB absent in these mutants is responsible for R perception in the N. plumbaginifolia seedling, but is not a R:FR sensor in light-grown plants.     

Overexpression of oat phytochrome A gene differentially affects stem growth responses to red/far-red ratio signals characteristic of sparse or dense canopies

The effects of overexpression of oat phytochrome A on neighbour detection and on stem-growth responses to changes in red light (R), far-red light (FR) and blue light (B) simulating neighbours were investigated in transgenic tobacco seedlings grown under natural radiation. In wild-type (WT) seedlings, stem extension growth was promoted: (1) by lowering the R:FR by means of daytime supplementary FR, end-of-day FR, neighbours reflecting FR, or selective light filters placed around the base of the shoot to reduce R without affecting FR; and (2) by lowering phytochrome-absorbable radiation (R+FR) reaching the stem. Transgenic seedlings only responded to reductions in R:FR involving no significant changes in FR irra-diance, i.e. end-of-day FR and filters placed around the stem to reduce R. Neither daytime supplementary R nor selective filters placed around the stem to reduce B affected stem growth in any genotype. In growing canopies, WT seedlings responded to the reduction of R:FR caused by FR reflected in neighbour plants. Transgenic seedlings responded to plant density about a week later, when mutual plant shading reduced R and (to a lesser extent) FR below sunlight levels. Overexpression of phytochrome A impaired early neighbour detection.