Identification of new susceptibility loci for IgA nephropathy in Han Chinese.

IgA nephropathy (IgAN) is one of the most common primary glomerulonephritis. Previously identified genome-wide association study (GWAS) loci explain only a fraction of disease risk. To identify novel susceptibility loci in Han Chinese, we conduct a four-stage GWAS comprising 8,313 cases and 19,680 controls. Here, we show novel associations at ST6GAL1 on 3q27.3 (rs7634389, odds ratio (OR)=1.13, P=7.27 × 10(-10)), ACCS on 11p11.2 (rs2074038, OR=1.14, P=3.93 × 10(-9)) and ODF1-KLF10 on 8q22.3 (rs2033562, OR=1.13, P=1.41 × 10(-9)), validate a recently reported association at ITGAX-ITGAM on 16p11.2 (rs7190997, OR=1.22, P=2.26 × 10(-19)), and identify three independent signals within the DEFA locus (rs2738058, P=1.15 × 10(-19); rs12716641, P=9.53 × 10(-9); rs9314614, P=4.25 × 10(-9), multivariate association). The risk variants on 3q27.3 and 11p11.2 show strong association with mRNA expression levels in blood cells while allele frequencies of the risk variants within ST6GAL1, ACCS and DEFA correlate with geographical variation in IgAN prevalence. Our findings expand our understanding on IgAN genetic susceptibility and provide novel biological insights into molecular mechanisms underlying IgAN.

DEFA gene variants associated with IgA nephropathy in a Chinese population.

IgA nephropathy (IgAN) is a complex syndrome with high genetic heterogeneity. More recently, a genome-wide association study (GWAS) from Southern Han population revealed that variants within 8p23.1, where the DEFA genes encoding a-defensins assembled, were associated with susceptibility to IgAN. To replicate the association and fine-map the genetic variants, a case-control genetic study from an independent Northern Han cohort was conducted. A total of 60 single-nucleotide polymorphisms in a region spanning 350 kb encompassing the DEFA genes cluster were analyzed in 2096 individuals. Copy number variations of DEFA1A3 within the loci were also checked for the independent association. Functional significance of the associated variants was further examined by the in silico method as well as by cis-acting expression quantitative trait loci analysis with mRNA. It showed that 17 out of 60 (28.3%) variants were associated with susceptibility to IgAN. Two independent signals with functional potentials were discovered (rs2738058, P=4.64 × 10(-5), odds ratio (OR)=0.76, 95% confidence interval (CI) 0.66-0.87 and rs9644778, P=4.78 × 10(-3), OR=1.21, 95% CI 1.06-1.39). Besides, marginally significant association of rs9644778 risk genotype with lower proportion of gross hematuria (CC+CA vs AA 35.2% vs 30.2%, P=0.073) was observed. In conclusion, DEFA gene polymorphisms have potentially pathogenic roles in IgAN, and the role of mucosal immunity in the pathogenesis of IgAN has to be emphasized.

DEF- and GLO-like proteins may have lost most of their interaction partners during angiosperm evolution.

BACKGROUND AND AIMS: DEFICIENS (DEF)- and GLOBOSA (GLO)-like proteins constitute two sister clades of floral homeotic transcription factors that were already present in the most recent common ancestor (MRCA) of extant angiosperms. Together they specify the identity of petals and stamens in flowering plants. In core eudicots, DEF- and GLO-like proteins are functional in the cell only as heterodimers with each other. There is evidence that this obligate heterodimerization contributed to the canalization of the flower structure of core eudicots during evolution. It remains unknown as to whether this strict heterodimerization is an ancient feature that can be traced back to the MRCA of extant flowering plants or if it evolved later during the evolution of the crown group angiosperms. METHODS: The interactions of DEF- and GLO-like proteins of the early-diverging angiosperms Amborella trichopoda and Nuphar advena and of the magnoliid Liriodendron tulipifera were analysed by employing yeast two-hybrid analysis and electrophoretic mobility shift assay (EMSA). Character-state reconstruction, including data from other species as well, was used to infer the ancestral interaction patterns of DEF- and GLO-like proteins. KEY RESULTS: The yeast two-hybrid and EMSA data suggest that DEF- and GLO-like proteins from early-diverging angiosperms both homo- and heterodimerize. Character-state reconstruction suggests that the ability to form heterodimeric complexes already existed in the MRCA of extant angiosperms and that this property remained highly conserved throughout angiosperm evolution. Homodimerization of DEF- and GLO-like proteins also existed in the MRCA of all extant angiosperms. DEF-like protein homodimerization was probably lost very early in angiosperm evolution and was not present in the MRCA of eudicots and monocots. GLO-like protein homodimerization might have been lost later during evolution, but very probably was not present in the MRCA of eudicots. CONCLUSIONS: The flexibility of DEF- and GLO-like protein interactions in early-diverging angiosperms may be one reason for the highly diverse flower morphologies observed in these species. The results strengthen the hypothesis that a reduction in the number of interaction partners of DEF- and GLO-like proteins, with DEF-GLO heterodimers remaining the only DNA-binding dimers in core eudicots, contributed to developmental robustness, canalization of flower development and the diversification of angiosperms.

Quantitative levels of Deficiens and Globosa during late petal development show a complex transcriptional network topology of B function.

The transcriptional network topology of B function in Antirrhinum, required for petal and stamen development, is thought to rely on initial activation of transcription of DEFICIENS (DEF) and GLOBOSA (GLO), followed by a positive autoregulatory loop maintaining gene expression levels. Here, we show that the mutant compacta (co), whose vegetative growth and petal size are affected, plays a role in B function. Late events in petal morphogenesis such as development of conical cell area and scent emissions were reduced in co and def (nicotianoides) (def (nic) ), and absent in co def (nic) double mutants, suggesting a role for CO in petal identity. Expression of DEF was down-regulated in co but surprisingly GLO was not affected. We investigated the levels of DEF and GLO at late stages of petal development in the co, def (nic) and glo-1 mutants, and established a reliable transformation protocol that yielded RNAi-DEF lines. We show that the threshold levels of DEF or GLO required to obtain petal tissue are approximately 11% of wild-type. The relationship between DEF and GLO transcripts is not equal or constant and changes during development. Furthermore, down-regulation of DEF or GLO does not cause parallel down-regulation of the partner. Our results demonstrate that, at late stages of petal development, the B function transcriptional network topology is not based on positive autoregulation, and has additional components of transcriptional maintenance. Our results suggest changes in network topology that may allow changes in protein complexes that would explain the fact that not all petal traits appear early in development.

Prognostic and predictive potential molecular biomarkers in colon cancer.

An important objective in nowadays research is the discovery of new biomarkers that can detect colon tumours in early stages and indicate with accuracy the status of the disease. The aim of our study was to identify potential biomarkers for colon cancer onset and progression. We assessed gene expression profiles of a list of 10 candidate genes (MMP-1, MMP-3, MMP-7, DEFA 1, DEFA-5, DEFA-6, IL-8, CXCL-1, SPP-1, CTHRC-1) by quantitative real time PCR in triplets of colonic mucosa (normal, adenoma, tumoral tissue) collected from the same patient during surgery for a group of 20 patients. Additionally we performed immunohistochemistry for DEFA1-3 and SPP1. We remarked that DEFA5 and DEFA6 are key factors in adenoma formation (p<0.05). MMP7 is important in the transition from a benign to a malignant status (p <0.01) and further in metastasis being a prognostic indicator for tumor transformation and for the metastatic potential of cancer cells. IL8, irrespective of tumor stage, has a high mRNA level in adenocarcinoma (p< 0.05). The level of expression for SPP1 is correlated with tumor level. We suggest that high levels of DEFAS, DEFA6 (key elements in adenoma formation), MMP7 (marker of colon cancer onset and progression to metastasis), SPP1 (marker of progression) and IL8 could be used to diagnose an early stage colon cancer and to evaluate the prognostic of progression for colon tumors. Further, if DEFA5 and DEFA6 level of expression are low but MMP7, SPP1 and IL8 level are high we could point out that the transition from adenoma to adenocarcinoma had already occurred. Thus, DEFA5, DEFA6, MMP7, IL8 and SPP1 consist in a valuable panel of biomarkers, whose detection can be used in early detection and progressive disease and also in prognostic of colon cancer.

Functional divergence within class B MADS-box genes TfGLO and TfDEF in Torenia fournieri Lind.

Homeotic class B genes GLOBOSA (GLO)/PISTILLATA (PI) and DEFICIENS (DEF)/APETALA3 (AP3) are involved in the development of petals and stamens in Arabidopsis. However, functions of these genes in the development of floral organs in torenia are less well known. Here, we demonstrate the unique floral phenotypes of transgenic torenia formed due to the modification of class B genes, TfGLO and TfDEF. TfGLO-overexpressing plants showed purple-stained sepals that accumulated anthocyanins in a manner similar to that of petals. TfGLO-suppressed plants showed serrated petals and TfDEF-suppressed plants showed partially decolorized petals. In TfGLO-overexpressing plants, cell shapes on the surfaces of sepals were altered to petal-like cell shapes. Furthermore, TfGLO- and TfDEF-suppressed plants partially had sepal-like cells on the surfaces of their petals. We isolated putative class B gene-regulated genes and examined their expression in transgenic plants. Three xyloglucan endo-1,4-beta-D: -glucanase genes were up-regulated in TfGLO- and TfDEF-overexpressing plants and down-regulated in TfGLO- and TfDEF-suppressed plants. In addition, 10 anthocyanin biosynthesis-related genes, including anthocyanin synthase and chalcone isomerase, were up-regulated in TfGLO-overexpressing plants and down-regulated in TfGLO-suppressed plants. The expression patterns of these 10 genes in TfDEF transgenic plants were diverse and classified into several groups. HPLC analysis indicated that sepals of TfGLO-overexpressing plants accumulate the same type of anthocyanins and flavones as wild-type plants. The difference in phenotypes and expression patterns of the 10 anthocyanin biosynthesis-related genes between TfGLO and TfDEF transgenic plants indicated that TfGLO and TfDEF have partial functional divergence, while they basically work synergistically in torenia.

Single nucleotide polymorphisms and the haplotype in the DEFB1 gene are associated with atopic dermatitis in a Korean population.

BACKGROUND: Atopic dermatitis (AD) patients have been recognized to have an increased susceptibility to cutaneous colonization and infection by bacteria, fungi and viruses. OBJECTIVE: We wanted to evaluate the associations of single nucleotide polymorphism (SNP) and the haplotype in the defensin (DEFA) and defensin (DEFB) genes, and so we performed genotyping for the SNPs in these genes in both AD patients and normal controls. METHOD: We genotyped 27 SNPs from the DEFA 4, 5 and 6 genes and the DEFB1 gene for 1089 case-control samples (631 AD patients and 458 normal controls). We analyzed the SNPs and haplotypes in each gene. RESULT: We identified that two SNPs and the haplotype CT in the DEFB1 gene are associated with AD in Koreans. The rs5743399 (-2266T/C) SNP is associated with AD, and especially with the high IgE, extrinsic type, and the rs5743409 (-1241T/G) SNP is associated with AD. On the haplotype analysis of these two SNPs, the haplotype CT is associated with AD, and especially with the allergic, extrinsic type of AD. However, we could not find any significant associations between the SNPs in the three DEFA genes and AD. CONCLUSION: We found that the rs5743399 SNP, the rs5743409 SNP and the CT haplotype in the DEFB1 gene were significantly associated with the susceptibility to AD. We also found that rs5743399 polymorphism and the haplotype CT in this gene showed a strong association with the allergic, extrinsic type of AD. These results suggest that the DEFB1 gene has a main effect on the skin inflammation and/or skin responsiveness to any kind of allergic reaction.

The S locus-linked Primula homeotic mutant sepaloid shows characteristics of a B-function mutant but does not result from mutation in a B-function gene.

Floral homeotic and flower development mutants of Primula, including double, Hose in Hose, Jack in the Green and Split Perianth, have been cultivated since the late 1500s as ornamental plants but until recently have attracted limited scientific attention. Here we describe the characterization of a new mutant phenotype, sepaloid, that produces flowers comprising only sepals and carpels. The sepaloid mutation is recessive, and is linked to the S locus that controls floral heteromorphy. The phenotype shows developmental variability, with flowers containing three whorls of sepals surrounding fertile carpels, two whorls of sepals with a diminished third whorl of sepals surrounding a fourth whorl of carpels, or three whorls of sepals surrounding abnormal carpels. In some respects, these phenotypes resemble the Arabidopsis and Antirrhinum homeotic B-function mutants apetala3/deficiens (ap3/def) and pistillata/globosa (pi/glo). We have isolated the Primula vulgaris B-function genes PvDEFICIENS (PvDEF) and PvGLOBOSA (PvGLO), expression of both of which is affected in the sepaloid mutant. PvGLO, like sepaloid, is linked to the S locus, whereas PvDEF is not. However, our analyses reveal that sepaloid and PvGLO represent different genes. We conclude that SEPALOID is an S-linked independent regulator of floral organ identity genes including PvDEF and PvGLO.

Characterization of genes controlling stamen identity and development in a parthenocarpic tomato mutant indicates a role for the DEFICIENS ortholog in the control of fruit set.

The development of the ovary into a fruit depends on pollination and fertilization. It has been proposed that the restriction of ovary growth before pollination is because of the stamens acting as negative regulators. Accordingly, the silencing of genes responsible for stamen identity has been correlated with parthenocarpy in different species. The tomato (Solanum lycopersicum L.) parthenocarpic fruit (pat) mutation associates autonomous ovary development with homeotic transformation of the anthers and aberrancy of ovules in the ovary. In this study, we tested the hypothesis that stamen aberrations and parthenocarpy in pat are driven by cues coming from the altered expression of class B MADS box genes. The data showed that the Pat locus is not allelic to either of the two tomato mutations putatively involved in the B function, stamenless (sl)-2 and pistillate (pi) or to genes encoding class B transcription factors. Whereas pat pi double mutants were not recovered because of tight linkage, pat sl-2 double mutants showed mainly epistatic effects. The developmental regulation of the Sl DEFICIENS (DEF) gene in the wild-type (WT) at anthesis as well as its differential transcription in the pat ovary suggest that it plays a role in the control of ovary growth. Accordingly, when compared with the WT, the gene was also differentially expressed in the parthenocarpic fruit-2 (pat-2) mutant, that is not allelic to pat and has normal ovule development. Altogether the results indicate that in tomato SlDEF plays a role in the control of ovary growth and that the pat mutation is located upstream of this regulatory cascade.

Phylogenetic utility of the AP3/DEF K-domain and its molecular evolution in Impatiens (Balsaminaceae).

APETALA3 (AP3)/DEFICIENS (DEF) is a MADS-box transcription factor that is involved in establishing the identity of petal and stamen floral organs. The AP3/DEF gene lineage has been extensively examined throughout the angiosperms in order to better understand its role in floral diversity and evolution. As a result, a large number of cloned AP3/DEF orthologues are available, which can be used for the design of taxon specific primers for phylogeny reconstruction of close relatives of the group of interest. Following this reasoning, we investigated the phylogenetic utility of the two AP3/DEF paralogues (ImpDEF1 and ImpDEF2) that were recently identified in the genus Impatiens (Balsaminaceae). K-domain introns 4 and 5 of both AP3/DEF duplicates were amplified and sequenced for 59 Impatiens species. Phylogenetic analyses of the separated and combined ImpDEF1 and ImpDEF2 data sets result in highly congruent topologies with the previously obtained chloroplast atpB-rbcL data set. Combination of chloroplast and nuclear matrices results in a well-supported evolutionary hypothesis of Impatiens. Our results show that introns 4 and 5 in AP3/DEF-like genes are a valuable source of characters for phylogenetic studies at the infrageneric level.

Validation by RQ-PCR and flow cytometry of alpha-defensin1-3 (DEFA1-3) overexpression in relapsed and refractory acute lymphoblastic leukemia.

In spite of high cure rates and improved overall survival, 25% of pediatric patients with acute lymphoblastic leukemia (ALL) relapse after obtaining complete remission. Additionally a small proportion of patients are refractory and do not attain remission. Microarray expression analysis of matched diagnosis-relapse B-lineage ALL sample pairs identified DEFA1-3 as a potential marker of relapse. Here, validation of DEFA1-3 as a marker for therapy resistance is explored. DEFA1-3 expression was analysed by RQ-PCR in patient paired samples at diagnosis and relapse of 6 early-relapse (within 18 months) and 8 late-relapse (beyond 18 months) B-lineage ALL. Diagnostic samples of 19 patients with ALL who are in continuous complete remission (median time from diagnosis 47 month) and diagnostic samples of 5 refractory patients who had not achieved remission at day 35 of therapy were also analyzed. In addition, overexpression of alpha-defensin1-3 proteins in blast cells at relapse was analysed by flow cytometry. DEFA1-3 was overexpressed at relapse as compared to diagnosis in 12 of 14 samples. At diagnosis, the expression of DEFA1-3 was significantly higher in samples from refractory patients as compared to those of patients who are in CR and to those of patients who experienced late relapse. At diagnosis, patients who relapsed early after diagnosis could not be distinguished from refractory patients based on DEFA1-3 expression levels. Results suggest that high levels of DEFA1-3 mRNA and alpha-defensin1-3 protein expression are correlated with disease progression and failure of adequate response to conventional chemotherapy.

The pollen-specific DEFH125 promoter from Antirrhinum is bound in vivo by the MADS-box proteins DEFICIENS and GLOBOSA.

The Antirrhinum DEFH125 MADS-box protein is expressed in maturing pollen and thus likely participates in the regulation of pollen development. Here, we describe the characterization of a 2.5 kbp promoter fragment conferring pollen-specific GUS expression in Antirrhinum, as well as in the distantly related species Arabidopsis. Taking advantage of the higher sensitivity of the diphtheria toxin A-chain (DTA) reporter gene assay, onset of DEFH125 promoter activity could be defined to start at the late unicellular microspore stage. Stamen development in Antirrhinum is governed by the class B MADS-box genes DEFICIENS (DEF) and GLOBOSA (GLO). The respective proteins form a heterodimer and are expressed throughout stamens, except for microspores. Complementary expression patterns of DEFH125 and DEF/GLO during later stamen development tempted us to investigate whether the DEF/GLO heterodimer might bind the DEFH125 promoter and could thus be involved in repressing the DEFH125 expression. The ChIP technique was applied to investigate protein/DNA interactions occurring in vivo. We report the identification of a 200 bp DEFH125 promoter fragment that is in vivo bound by DEF and GLO proteins. This fragment contains a CArG-box motif, known to mediate DNA binding of MADS-box proteins. Implications for a likely function of DEF and GLO in the transcriptional control of DEFH125 are discussed.

The modified ABC model explains the development of the petaloid perianth of Agapanthus praecox ssp. orientalis (Agapanthaceae) flowers.

The class B genes, which belong to the MADS-box gene family, play important roles in regulating the development of petals and stamens in flowering plants. To understand the molecular mechanisms of floral development in Agapanthus praecox ssp. orientalis (Agapanthaceae), we isolated and characterized the homologs of the Antirrhinum majus genes GLOBOSA and DEFICIENS in this plant. These were designated as ApGLO and ApDEF, respectively. ApGLO and ApDEF contain open reading frames that encode deduced protein with 210 and 214 amino acid residues, respectively. Phylogenetic analysis indicated that ApGLO and ApDEF belong to the monocot class B gene family. In situ hybridization experiments revealed that hybridization signals of ApGLO and ApDEF were observed in whorl 1 as well as in whorls 2 and 3. Moreover, the flowers of transgenic Arabidopsis plants that ectopically expressed ApGLO formed petal-like organs in whorl 1. These observations indicate that the flower developmental mechanism of Agapanthus follows the modified ABC model.

To B or Not to B a flower: the role of DEFICIENS and GLOBOSA orthologs in the evolution of the angiosperms.

DEFICIENS (DEF) and GLOBOSA (GLO) function in petal and stamen organ identity in Antirrhinum and are orthologs of APETALA3 and PISTILLATA in Arabidopsis. These genes are known as B-function genes for their role in the ABC genetic model of floral organ identity. Phylogenetic analyses show that DEF and GLO are closely related paralogs, having originated from a gene duplication event after the separation of the lineages leading to the extant gymnosperms and the extant angiosperms. Several additional gene duplications followed, providing multiple potential opportunities for functional divergence. In most angiosperms studied to date, genes in the DEF/GLO MADS-box subfamily are expressed in the petals and stamens during flower development. However, in some angiosperms, the expression of DEF and GLO orthologs are occasionally observed in the first and fourth whorls of flowers or in nonfloral organs, where their function is unknown. In this article we review what is known about function, phylogeny, and expression in the DEF/GLO subfamily to examine their evolution in the angiosperms. Our analyses demonstrate that although the primary role of the DEF/GLO subfamily appears to be in specifying the stamens and inner perianth, several examples of potential sub- and neofunctionalization are observed.

Characterization of antirrhinum petal development and identification of target genes of the class B MADS box gene DEFICIENS.

The class B MADS box transcription factors DEFICIENS (DEF) and GLOBOSA (GLO) of Antirrhinum majus together control the organogenesis of petals and stamens. Toward an understanding of how the downstream molecular mechanisms controlled by DEF contribute to petal organogenesis, we conducted expression profiling experiments using macroarrays comprising >11,600 annotated Antirrhinum unigenes. First, four late petal developmental stages were compared with sepals. More than 500 ESTs were identified that comprise a large number of stage-specifically regulated genes and reveal a highly dynamic transcriptional regulation. For identification of DEF target genes that might be directly controlled by DEF, we took advantage of the temperature-sensitive def-101 mutant. To enhance the sensitivity of the profiling experiments, one petal developmental stage was selected, characterized by increased transcriptome changes that reflect the onset of cell elongation processes replacing cell division processes. Upon reduction of the DEF function, 49 upregulated and 52 downregulated petal target genes were recovered. Eight target genes were further characterized in detail by RT-PCR and in situ studies. Expression of genes responding rapidly toward an altered DEF activity is confined to different petal tissues, demonstrating the complexity of the DEF function regulating diverse basic processes throughout petal morphogenesis.

Virus induced gene silencing of a DEFICIENS ortholog in Nicotiana benthamiana.

Traditionally, developmental studies in plant biology have suffered from the lack of a convenient means to study gene function in non-model plant species. Here we show that virus-induced gene silencing (VIGS) is an effective new tool to study the function of orthologs of floral homeotic genes such as DEFICIENS (DEF) in non-model systems. We used a tobacco rattle virus (TRV)-based VIGS approach to study the function of the Nicotiana benthamiana DEF ortholog (NbDEF). Silencing of NbDEF in N. benthamiana using TRV-VIGS was similar to that of Antirrhinum def and Arabidopsis ap3 mutants and caused transformation of petals into sepals and stamens into carpels. Molecular analysis of the NbDEF -silenced plants revealed a dramatic reduction of the levels of NbDEF mRNA and protein in flowers. NbDEF silencing was specific and has no effect on the mRNA levels of NbTM6, the closest paralog of NbDEF. A dramatic reduction of the levels of N. benthamiana GLOBOSA (NbGLO) mRNA and protein was also observed in flowers of NbDEF-silenced plants, suggesting that cross-regulation of this GLO-like gene by NbDEF. Taken together, our results suggest that NbDEF is a functional homolog of Antirrhinum DEF. Our results are significant in that they show that TRV efficiently induces gene silencing in young and differentiating flowers and that VIGS is a promising new tool for analyses of developmental gene function in non-model organisms.

Mitochondrial tuning fork in nuclear homeotic functions.

Homeotic-like flower morphologies in plants with cytoplasmic male sterility (CMS) are maternally inherited and associated with rearrangements in mitochondrial DNA. Recent studies allow an interpretation of dramatic CMS morphologies in the light of the floral ABC model. They uncover new nuclear targets for interactions with mitochondrial genes. GLOBOSA-, DEFICIENS- and APETALA3-like genes were transcriptionally down-regulated in carpelloid CMS flowers of tobacco, carrot and wheat. These results allow cooperation between nuclear and cytoplasmic genetic compartments considered as a developmental function and an evolutionary mechanism of speciation.

Structural diversification and neo-functionalization during floral MADS-box gene evolution by C-terminal frameshift mutations.

Frameshift mutations generally result in loss-of-function changes since they drastically alter the protein sequence downstream of the frameshift site, besides creating premature stop codons. Here we present data suggesting that frameshift mutations in the C-terminal domain of specific ancestral MADS-box genes may have contributed to the structural and functional divergence of the MADS-box gene family. We have identified putative frameshift mutations in the conserved C-terminal motifs of the B-function DEF/AP3 subfamily, the A-function SQUA/AP1 subfamily and the E-function AGL2 subfamily, which are all involved in the specification of organ identity during flower development. The newly evolved C-terminal motifs are highly conserved, suggesting a de novo generation of functionality. Interestingly, since the new C-terminal motifs in the A- and B-function subfamilies are only found in higher eudicotyledonous flowering plants, the emergence of these two C-terminal changes coincides with the origin of a highly standardized floral structure. We speculate that the frameshift mutations described here are examples of co-evolution of the different components of a single transcription factor complex. 3' terminal frameshift mutations might provide an important but so far unrecognized mechanism to generate novel functional C-terminal motifs instrumental to the functional diversification of transcription factor families.

Interactions between gene activity and cell layers during floral development.

The DEFICIENS (DEF) gene is required for establishing petal and stamen identity in Antirrhinum and is expressed in all three layers of the floral meristem in whorls 2 and 3. Expression of DEF in a subset of meristem layers gives rise to organs with characteristic shapes and cell types, reflecting altered patterns and levels of DEF gene activity. To determine how the contributions of layers and gene activity interact, we exploited a DEF allele which carries a transposon insertion in the MADS box region to generate periclinal chimeras expressing alleles with different activities. By comparing the phenotype, development and expression patterns of these chimeras we show that expression of DEF in L1 makes a major contribution to morphology in whorl 2, irrespective of the allele. By contrast L1 expression is largely unable to rescue whorl 3, possibly because of a non-autonomous inhibitor of DEF activity in this whorl.

Flower development in carrot CMS plants: mitochondria affect the expression of MADS box genes homologous to GLOBOSA and DEFICIENS.

Maternally inherited defects in the formation of male flower organs leading to cytoplasmic male sterility (CMS) indicate an involvement of mitochondrial genes in the control of flower formation. In the 'carpeloid' CMS type of carrot, stamens are replaced by carpels. The florets thus resemble well-investigated homeotic flower mutants of Arabidopsis and Antirrhinum, in which organ identity is impaired because of the mutation of specific nuclear MADS box genes. We have isolated five cDNAs encoding MADS box proteins (DcMADS1-5) from a flower-specific library of carrot. Structural features deduced from their sequence and transcript patterns in unmodified carrot flowers determined by in situ hybridisation relate them to known MADS box transcription factors involved in specification of flower organs. In 'carpeloid' CMS flowers, we detected a distinctly reduced expression of DcMADS2 and DcMADS3, homologues of the Antirrhinum genes GLOBOSA and DEFICIENS. Our data strongly suggest that the 'carpeloid' CMS phenotype is caused by a cytoplasmic (mitochondrial) effect on the expression of two MADS box factors specifying organ development at whorls 2 and 3 of carrot flowers.