TCP Transcription Factors Control the Morphology of Shoot Lateral Organs via Negative Regulation of the Expression of Boundary-Specific Genes in Arabidopsis W OA
Tomotsugu Koyama,a,b Masahiko Furutani,c Masao Tasaka,c and Masaru Ohme-Takagi a,b,1
a Rearch Institute of Genome-Bad Biofactory,National Institute of Advanced Industrial Science and Technology, Tsukuba,Ibaraki305-8566,Japan
b Core Rearch for Evolutional Science and Technology,Japan Science and Technology Agency,Kawaguchi,Saitama,
332-0012,Japan
c Nara Institute of Science an
d Technology,Graduat
e School o
f Biological Sciences,Ikoma,Nara630-0101,Japan
骆驼祥子好句
Plants form shoot meristems in the so-called boundary region,and the meristems are necessary for normal morphogenesis of aerial parts of plants.However,the molecular mechanisms that regulate the formation of shoot meristems are not fully understood.We report here that expression of a chimeric repressor from TCP3(TCP3SRDX),a member of TEOSINTE BRANCHED1,CYCLOIDEA,and PCF(TCP)transcription factors in Arabidopsis thaliana,resulted in the formation of ectopic shoots on cotyledons and various defects in organ development.Expression of TCP3SRDX induced ectopic expression of boundary-specific genes,namely the CUP-SHAPED COTYLEDON(CUC)genes,and suppresd the expression of miR164, who product cleaves the transcripts of CUC genes.This abnormal phenotype was substantially reverd on the cuc1mutant background.By contrast,gain of function of TCP3suppresd the expression of CUC genes and resulted in the fusion of cotyledons and defects in formation of shoots.The pattern of expression of TCP3did not overlap with that of the CUC genes.In addition,we found that eight TCPs had functions similar to that of TCP3.Our results demonstrate that the TCP transcription factors play a pivotal role in the control of morphogenesis of shoot organs by negatively regulating the expression of boundary-specific genes.
INTRODUCTION
行走作文
Meristems are compod of small populations of undifferentiated cells.Plants can regenerate entire organs from shoot meristems via the production of organ primordia.Once organ primordia have been generated,they differentiate into various organs according to their specified fates and cannot return to the meristematic pha during normal development.Lateral organ primordia are established in the peripheral region of a shoot meristem,which is associated with the formation of boundaries that parate organ primordia from the shoot meristem(Aida and Tasaka,2006a, 2006b).In dicotyledonous plants,a shoot apical meristem(SAM) is formed in the boundary region of two cotyledonary primordia during embryogenesis,and condary shoot meristems are formed at the boundary of stems and leaves,namely,at leaf axils. Several factors have been identified as regulators of the formation of shoot meristems in boundary regions.The expres-sion of boundary-specific genes for NAC domain transcription factors,namely,NO APICAL MERISTEM,CUP-SHAPED COTY-LEDON(CUC),and CUPULIFORMIS in petunia(Petunia hybrida), Arabidposis thaliana,and Antirrhinum majus,respectively,is necessary for the initiation of formation of shoot meristems (Souer et al.,1996;Aida et al.,1997;Vroemen et al.,2003;Weir et al.,2004).Moreover,loss of expression of two of the three CUC genes in Arabidopsis results in the fusion of cotyledons and defects in the formation of the SAM(Aida et al.,1997;Vroemen et al.,2003).By contrast,ectopic expression of CUC1enhances the expression of class I KNOTTED1-like homeobox(KNOX) genes and induces the
formation of ectopic shoots on the adaxial surface of Arabidopsis cotyledons(Takada et al.,2001;Hibara et al.,2003).This obrvation indicates that the expression of the CUC1gene is sufficient for the induction of formation of ectopic shoots on cotyledons.The expression of CUC genes is detected only at the boundaries of embryonic cotyledonary primordia and postembryonic organs,such as leaf axils andfloral organs(Aida et al.,1999;Takada et al.,2001;Vroemen et al.,2003;Hibara et al.,2006).Thus,the spatially restricted expression of CUC genes is important for the formation of a shoot meristem at a defined position.Although it has been suggested that the auxin respon pathway and microRNA(miRNA)might be involved in the control of the expression of CUC genes(Vernoux et al.,2000; Aida et al.,2002;Furutani et al.,2004;Laufs et al.,2004;Mallory et al.,2004;Baker et al.,2005),the molecular mechanisms that regulate the spatial expression of CUC genes,which are involved in the formation of shoot meristems,remain unknown.
1To whom correspondence should be addresd.E-mail m-takagi@
The author responsible for distribution of materials integral to the
findings prented in this article in accordance with the policy described
in the Instructions for Authors(www.plantcell)is:Masaru Ohme-
Takagi(jp).
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www.plantcell/cgi/doi/10.1105/tpc.106.044792
The Plant Cell,Vol.19:473–484,February2007,www.plantcellª2007American Society of Plant Biologists
The TEOSINTE BRANCHED1,CYCLOIDEA,and PCF(TCP) family of transcription factors has been reported to play roles in various aspects of plant development(Luo et al.,1996;Doebley et al.,1997;Kosugi and Ohashi,1997;Cubas et al.,1999).Loss of function of a TCP gene,the CINCINNATA(CIN)gene,in Antir-rhinum results in the abnormal curvature of leaves and petals (Nath et al.,2003;Crawford et al.,2004).In addition,suppression of the expression of TCP genes by the ectopic expression of miR319/JAW,which targets TCP2,TCP3,TCP4,TCP10,and TCP24genes,induced a cin-like phenotype in Arabidopsis (Palatnik et al.,2003).The Arabidopsis gen
ome contains24 TCP genes,which have been classified into the CYC/TB and PCF subfamilies(e Supplemental Figure1online;Cubas,2000). However,the functional roles of members of the TCP family, including CIN,remain to be clarified.读书诗
We developed a gene silencing system,designated chimeric repressor gene-silencing technology(CRES-T),in which a tran-scription factor fud to the EAR-motif repression domain(SRDX) dominantly repress the transcription of its target genes,even in the prence of endogenous and functionally redundant tran-scription factors(Hiratsu et al.,2003).Using the CRES-T system, which involves generation of a dominant repressor,we have obtained some insights into the function of TCPs in the regulation of morphogenesis of shoot lateral organs,including the formation of the shoot meristems,via negative control of the expression of boundary-specific genes.
RESULTS
The Chimeric TCP3Repressor Induces the Formation
of Ectopic Shoots
As part of our efforts to identify the biological functions of TCP transcription factors,we applied our C
RES-T system to TCP transcription factors becau we obrved no visible abnormal phenotypic features in either Arabidopsis T-DNA–tagged lines for the TCP genes(data not shown).We converted TCP3,which is phylogenetically clo to CIN(e Supplemental Figure1online), into a chimeric repressor by fusing it with the SRDX repression domain(Hiratsu et al.,2003),and we expresd the fud gene under the control of the cauliflower mosaic virus(CaMV)35S promoter(35S:TCP3SRDX;Figure1A)in Arabidopsis.Expres-sion of TCP3SRDX induced various morphological abnormalities, which were specifically evident on the surface and at the margins of various organs.Cotyledons of35S:TCP3SRDX plants were wavy,rrated,and much smaller than tho of the wild type,and a number of ectopic shoots were generated on the adaxial side of the cotyledons(Figures1B to1E).The abnormal phenotypes of 35S:TCP3SRDX edlings could be grouped into three class according to the verity of abnormalities.Seedlings with a mildly abnormal phenotype had epinastic cotyledons with indistinctly differentiated petioles and blades but no ectopic shoots(Figure 1C).Seedlings with a moderate phenotype had cotyledons with rrations at their margins and many ectopic shoots(Figure1D). The edlings with a vere phenotype had multiple ectopic shoots on their cotyledons,which resulted in defects in the expansion of the cotyledon(Figures1E and2B).In addition,we often obrved ectopic trichomes on the surface of the cotyle-dons(Figure2B).Severe defects in the elongation of the main root were also frequent(e Sup
plemental Figure2online),and the pattern of vein formation was verely disrupted in the cotyle-dons of35S:TCP3SRDX plants(Figures1F and1G).Becau the defects in the cotyledons were also evident in mature embryos (Figures1H and1I),we postulated that the abnormal develop-ment of the cotyledons in35S:TCP3SRDX plants occurred during embryogenesis.
The edlings of35S:TCP3SRDX plants with a mild phenotype grew relatively normally,but their rotte leaves were wavy and rrated(Figures1J and1K),rembling tho of jaw-D plants (Palatnik et al.,2003).The35S:TCP3SRDX plants with a moder-ate or vere phenotype often failed to grow when transferred to soil,and tho that developed to rotte plants usually had a bushy phenotype,which was probably due to the prence of ectopic shoots and suggested that the ectopic shoots induced by TCP3SRDX had functional meristems(Figures1L and1M). Ectopic shoots were occasionally generated,but at low fre-quency,on the leaves of35S:TCP3SRDX plants(data not shown). The morphology of thefloral organs of35S:TCP3SRDX plants was verely abnormal(Figures1N to1U).The pals and petals were wavy and rrated(Figures1Q and1S),and the stamens often had clumped outgrowths of cells on their anthers(Figure 1U).Carpels of35S:TCP3SRDX plants appeared normal,but the surface of siliques was crinkled and the siliques were significantly shorter than tho of the wild type(Figure1V).The results indicated that TCP3SR
DX was able to induce abnormal devel-opment in various organs,regardless of their identity. Obrvations by scanning electron microscopy revealed that wild-type cells in the epidermis and the marginal region were organized in a specific pavement-like pattern and were rod-shaped,respectively,whereas the cells of35S:TCP3SRDX plants were rounded both in the epidermis and in the marginal regions,with features of undifferentiated cell clusters(Figures2C to2F;Donnelly et al.,1999;Ori et al.,2000).Becau the differentiation of cells is regulated by their relative position within an organ(Donnelly et al.,1999;Ori et al.,2000),the obrva-tions suggested that the epidermal cells of35S:TCP3SRDX plants do not undergo position-dependent differentiation.
A transient expression assay revealed that TCP3had trans-activation activity and that TCP3SRDX acted as a repressor in Arabidopsis leaves(e Supplemental Figure3online).In addi-tion,TCP3mSRDX,in which the encoded amino acid quence of the SRDX repression domain was mutated(mSRDX;Hiratsu et al.,2004),had no repressive activity(e Supplemental Figure 3online).We confirmed that the expression of35S:TCP3mSRDX in transgenic Arabidopsis was unable to induce morphological defects in cotyledons and in leaves(data not shown).The results indicated that the phenotype of35S:TCP3SRDX plants was induced by the repressive activity of TCP3SRDX and not by some nonspecific negative effect(s),such as squelching(Cahill et al.,1994).
We expresd TCP3SRDX under the control of the59-up-stream region of the TCP3gene(Pro TCP3:TCPS3RDX),instead of the CaMV35S promoter,to examine the activity of TCP3SRDX in a condition similar to that of native TCP3.We found that Pro TCP3:TCPS3RDX plants had the same phenotype as that of 35S:TCP3SRDX plants,although the frequency of the moderate
474The Plant Cell
and verer phenotypes was lower than in the ca of 35S:TCP3SRDX plants (Figure 3).Pro TCP3:TCPS3RDX plants with a mild or a moderate phenotype had leaves pals,petals,and siliques with wavey surfaces and rrated margins (Figures 3C to 3G).The results indicate that TCP3SRDX,which is prent at a concentration more similar to that of the corresponding native transcription factor,could induce the defective phenotype.
TCP3Regulates the Expression of Boundary-Specific Genes
The 35S:TCP3SRDX plants were morphologically similar to transgenic plants that expresd CUC1(35S:CUC1)ectopically with respect to the formation of ectopic shoots on the adaxial surface of cotyledons,wavy margins,irregular formation
of
Figure 1.Abnormal Phenotype of Various Organs Induced by TCP3SRDX.
(A)Schematic reprentation of the 35S:TCP3SRDX gene.CaMV 35S,V ,SRDX,and nos reprent the CaMV 35S promoter,the translational enhancer of Tobacco mosaic virus ,the repression domain of 12amino acids,and the terminator quence of the NOS gene,respectively.
(B)to (E)Seedlings of wild-type (B)and 35S:TCP3SRDX plants with the mild (C),moderate (D),and vere (E)phenotypes.The asterisks and arrows in (D)indicate lobes and ectopic shoots of cotyledons,respectively.
(F)and (G)The patterns of vasculature in edlings of wild-type (F)and 35S:TCP3SRDX (G)plants.(H)and (I)Mature embryos of the wild-type (H)and the T2generation of 35S:TCP3SRDX (I)plants.
(J)to (M)A rotte and leaf of a wild-type plant (J)and of 35S:TCP3SRDX plants with the mild (K),moderate (L),and vere (M)phenotypes.The plants shown were 3weeks old.
(N)and (O)Flowers of wild-type (N)and 35S:TCP3SRDX (O)plants.
(P)and (Q)The adaxial surface of pals of wild-type (P)and 35S:TCP3SRDX (Q)plants.Asterisks indicate rration of the margin.(R)and (S)Petals of wild-type (R)and 35S:TCP3SRDX (S)plants.
(T)and (U)Stamens of wild-type (T)and 35S:TCP3SRDX (U)plants.Arrows in (U)indicate outgrowths on the anther.(V)Siliques of wild-type (bottom panel)and 35S:TCP3SRDX (top panel)plants.st,style.
Bars ¼0.5mm in (B)to (G)and (M)to (U),0.1mm in (H)and (I),and 10mm in (J)to (L)and (V).
Control of Shoot Morphology by TCPs 475
vasculature,and the undifferentiated rounded shape of epider-mal cells (Takada et al.,2001;Hibara et al.,2003).To analyze the effects of TCP3on the regulation of the spatial expression of CUC1,we introduced TCP3SRDX into an enhancer trap line of CUC1,namely,M0223(Cary et al.,2002).In M0223plants,we only detected the promoter activity,as displayed by the fluores-cence of green fluorescent protein,in the boundary region between two cotyledons (Figure 4A).By contrast,the region in which CUC1was expresd had expanded broadly in cotyledons of M0223plants that had been transformed with the TCP3SRDX construct (Figure 4B).Rembling results for the CUC1gene,the areas of expression of two other boundary-specific genes,CUC3and LATERAL ORGAN BOUNDARIES (LOB )(Shuai et al.,2002;Vroemen et al.,2003),as reprented by signals du
e to b -glucuronida (GUS)in the enhancer trap WET368and ET22lines,respectively,were broadly expanded in the cotyledons of the respective enhancer trap lines,when TCP3SRDX was ex-presd after it had been introduced by transformation (Figure 4C to 4F).In addition,inappropriate expression of CUC3was also apparent in mature leaves and pals of the WET368line in association with the expression of TCP3SRDX ,while no expres-sion of CUC3was evident in leaves and pals in the abnce of the TCP3SRDX transgene (Figures 4G to 4K).Cells in leaves in which the CUC3gene was ectopically expresd were often rounded (Figure 4I),suggesting that the expression of the boundary-specific genes induced an undifferentiated state in the cells.Analysis of the expression of transcripts revealed that the boundary-specific genes CUC1,CUC3,CYP78A5,LOB ,LATERAL SUPPRESSOR ,and BLADE ON PETIOLE1(BOP1)(Aida et al.,1997;Zondlo and Irish,1999;Shuai et al.,2002;Greb et al.,2003;Vroemen et al.,2003;Ha et al.,2004)were expresd in leaves of 35S:TCP3SRDX plants,whereas the genes were not expresd in leaves of wild-type plants (Figure 4N).Similarly,the CUC1,CUC3,and LOB genes were also expresd ectop-ically in the cotyledons of Pro TCP3:TCP3SRDX plants (e Sup-plemental Figure 4online).The results indicate that TCP3SRDX induced the ectopic expression of a variety of boundary-specific genes in a variety of organs.
In addition to its effect on boundary-specific genes,we exam-ined the effect of TCPSRDX on the expression of class I KNOX genes,namely,KNAT1,KNAT2,and SHOOT MERISTEMLESS (STM ),which is required for the formation of a functional meristem (Chuck et al.,1996;Ori et al.,2000;Hake et al.,2004).The promoter activity of KNAT1was detected only in the SAM of Pro KNAT1
:GUS一个月来两次月经
Figure 2.Scanning Electron Microscopy Analysis of Wild-Type and 35S:TCP3SRDX Shoot Lateral Organs.
(A)and (B)Seedlings of a wild-type plant (A)and a 35S:TCP3SRDX plant with the vere phenotype (B).Ct,cotyledonary blades that had emerged from the same layer of the hypocotyl.Arrows indicate ectopic trichomes.A cotyledonary blade at the position of the arrowhead was detached to allow visua
陷阱英语lization of the interior.Bars ¼200m m.
(C)and (D)The adaxial surface of cotyledons of wild-type (C)and 35S:TCP3SRDX (D)plants.Asterisks in (D)indicate clusters of rounded cells.St,ectopic shoots.
(E)and (F)Marginal regions of wild-type (E)and 35S:TCP3SRDX (F)leaves.Arrows in (E)indicate rod-shaped cells that were typically obrved in marginal regions and tho in (F)indicate curling of the marginal region.Bars ¼50m m in (C)to (F)
.
Figure 3.Phenotype of Pro TCP3:TCP3SRDX Plants.
(A)and (B)Seedlings with irregular differentiation of the petiole,as indicated by arrows (A),and with ectopic shoots on the cotyledon,as indicated by an asterisk (B).
(C)The rotte of a Pro TCP3:TCP3SRDX plant.(D)A leaf of a Pro TCP3:TCP3SRDX plant.
(E)A pal of a Pro TCP3:TCP3SRDX plant.Asterisks indicate rrations.(F)A petal of a Pro TCP3:TCP3SRDX plant.
(G)Siliques of a wild-type (left)and a Pro TCP3:TCP3SRDX (right)plant.The silique on the right is shorter and has a crinkled surface.
Bars ¼0.5mm in (A),(B),(E),and (F)and 10mm in (C),(D),and (G).
一般位置直线476The Plant Cell
plants,while the region in which KNAT1was expresd was much more extensive in the prence of
粉彩笔TCP3SRDX (Figures 4L and 4M).In addition,analysis by RT-PCR showed that KNAT1,KNAT2,and STM were expresd ectopically in leaves of 35S:TCP3SRDX plants (Figure 4N).Since the product of the CUC1gene is a positive regulator of the expression of class I KNOX genes (Takada et al.,2001;Hibara et al.,2003),it ems likely that enhanced expression of boundary-specific genes,including the CUC1gene,in respon to TCP3SRDX induced the inappropriate expression of the class I KNOX genes in 35S:TCP3SRDX plants.
小学作文评分标准
The expression of CUC genes is negatively regulated by miR164(Laufs et al.,2004;Mallory et al.,2004;Baker et al.,2005).To investigate whether TCP3is involved in the accumu-lation of miR164,we examined levels of miR164in 35S:TCP3SRDX plants.RNA gel blot analysis revealed a significant
reduction in the accumulation of miR164in 35S:TCP3SRDX plants (Figure 5),suggesting the involvement of TCP3in the regulation of the accumulation of this miRNA.
Loss of CUC Activity Suppress the Function of the Chimeric TCP3Repressor
To confirm that the abnormal phenotype of 35S:TCP3SRDX plants was due to the inappropriate expression of boundary-specific genes,we expresd TCP3SRDX in plants with a loss-of-function m
utation in a boundary-specific gene.When TCP3SRDX was expresd on the cuc1mutant background,the defective phenotype of cotyledons of 35S:TCP3SRDX plants was sup-presd to a considerable extent and most of the edlings had normal cotyledons with a flat surface and smooth margins,
with
Figure 4.The Effects of TCP3SRDX on the Pattern of Expression of Boundary-Specific Genes and Class I KNOX Genes.
(A)and (B)Expression of CUC1in a edling of the M0223line,an enhancer trap line of CUC1(C24background)(A),and that in a similar edling that expresd TCP3SRDX (B).
(C)and (D )Expression of CUC3in a edling of the WET368line,an enhancer trap line of CUC3(Landsberg erecta [L er ]background)(C),and that of the same line that expresd TCP3SRDX (D).
(E)and (F)Expression of LOB in a edling of the ET22line,an enhancer trap line of LOB (L er background)(E),and that of the same line that expresd TCP3SRDX (F).
(G)and (H)Expression of CUC3in rotte leaves of the WET368line (G)and of the WET368line that expresd TCP3SRDX (H).(I)A magnified view of curling of the leaf margin in (H).
(J)and (K)Expression of CUC3in pals of the WET368line (J)and in pals of the same line that expresd TCP3SRDX (K).A strong GUS signal was detected between ovules,as reported previousl
y (Vroemen et al.,2003).
(L)and (M)Expression of KNAT1in a Pro KNAT1:GUS edling (L)and in a similar edling that expresd TCP3SRDX (M).
(N)Analysis of the expression of boundary-specific genes and class I KNOX genes by RT-PCR.Lane 1,RNA isolated from wild-type edlings as a positive control for boundary-specific genes;lane 2,RNA from wild-type leaves;and lane 3,RNA from 35S:TCP3SRDX leaves.Expression of the gene for Tubulin (TUB )was monitored as an internal control.
Bars ¼0.5mm in (A)to (F)and (J)to (M)and 5mm in (H)and (I).
Control of Shoot Morphology by TCPs 477
no ectopic shoots (Figures 6A and 6B).Such recovery was obrved similarly on the cuc2mutant background,but the fre-quency of recovery was lower than on the cuc1mutant back-ground (Figure 6C).By contrast,no recovery was obrved on the bop1-4mutant background (data not shown).The results indicated that the abnormal phenotype of 35S:TCP3SRDX plants was most likely due to the inappropriate expression of the CUC genes.
Gain of Function of TCP3Suppress the Formation of Shoot Meristems
Transgenic plants that expresd TCP3ectopically (35S:TCP3)had no visible abnormalities,probably as a result of the activity of miR319/JAW (data not shown).Therefore,we expresd a mu-tant form of TCP3(mTCP3)in which the target site of miR319/
JAW had been replaced by a nontarget quence,without any change in the encoded amino acid quence,as described previously in the ca of TCP2and TCP4(Palatnik et al.,2003).We found that 35S:mTCP3induced the fusion of cotyledons and defects in the formation of shoots,in addition to enhanced elongation of hypocotyls (Figures 7A to 7C).This phenotype was somewhat similar to that of the cuc1cuc2double mutant.Similar fusion of cotyledons was also obrved in 35S:mTCP2and 35S:mTCP4plants to varying degrees (Palatnik et al.,2003;e Supplemental Figure 5online).In edlings of the plants,the expression of CUC1and CUC3was significantly suppresd or undetectable (Figure 7D;e Supplemental Figure 5online).Analysis by RT-PCR confirmed that the level of the expression of the CUC genes was clearly reduced in 35S:mTCP3plants (data not shown).The results demonstrated that TCP3,in addition to TCP2and TCP4,can suppress the expression of CUC genes.Redundant Functions of the Members of the TCP Family As compared with transgenic plants that expresd TCP3SRDX,we found that tcp3-1plants,namely,the TCP3T-DN
A–tagged homozygous line (CS855978),and transgenic plants that ex-presd the double-stranded RNA for RNA interference (RNAi)of the TCP3gene had basically normal cotyledons (e Supple-mental Figure 6online).By contrast,ectopic expression of a genomic DNA fragment that encoded miR319/JAW,which should cleave transcripts of the TCP2,TCP3,TCP4,TCP10,and TCP24genes,resulted in cotyledons that rembled tho of 35S:TCP3SRDX plants with the mild phenotype (e Supple-mental Figure 6online),in addition to an effect on leaf
phenotype,
Figure 5.TCP3SRDX Suppresd the Accumulation of miR164.(A)RNA gel blot analysis for the detection of miR164in wild-type and 35S:TCP3SRDX plants.5S rRNA was ud as an ,nucleotides.
(B)Quantitative analysis of the accumulation of miR164in wild-type and 35S:TCP3SRDX plants.The intensity of the signal due to miR164is shown relative to that due to 5S rRNA.The relative value for the wild type was t at 100.The error bar indicates the SD of results from three independent
experiments.
Figure 6.Mutations in CUC Genes Suppresd the Activity of TCP3SRDX.
(A)A 35S:TCP3SRDX L er edling with abnormal cotyledons and ectopic shoots.
(B)A 35S:TCP3SRDX cuc1edling,showing cotyledons with normal morphology.Bars ¼0.5mm in (A)and (B).
(C)Schematic reprentation of the frequency of reversal of the abnor-mal phenotype of 35S:TCP3SRDX edlings by mutations in CUC genes.Phenotypic verity was classified as indicated in Figures 1C to 1E.Open box,similar to the wild type;striped box,mild phenotype;gray box,moderate phenotype;and clod box,vere phenotype.The number of edlings examined is given in parenthesis in each ca.The data are given as percentages.The background of the cuc mutants was the L er ecotype.
478The Plant Cell
