APETALA1突变影响WRKY基因的基础表达

拟南芥APETALA1（AP1）既是一个花分生组织特征基因又是一个花器官特征基因,在花器官发育中控制花萼和花瓣的发育。通过GUS染色进一步证实AP1主要在茎尖、花萼、花瓣和花托的位置表达。启动子分析发现,AP1启动子区包含了包括W-box在内的大量顺式作用元件,暗示相关转录调控因子参与了对AP1的调控。21个WRKY基因单突变后并不改变AP1在花中的表达,但是AP1突变则增强了检测的10个WRKY基因中7个WRKY基因的表达,暗示AP1参与了对WRKY基因的基础表达的调控。这个结果也暗示AP1可能通过控制花萼和花瓣的发育从而参与了对花的基础抗性。     

Poppy APETALA1/FRUITFULL orthologs control flowering time, branching, perianth identity, and fruit development

Several MADS box gene lineages involved in flower development have undergone duplications that correlate with the diversification of large groups of flowering plants. In the APETALA1 gene lineage, a major duplication coincides with the origin of the core eudicots, resulting in the euFUL and the euAP1 clades. Arabidopsis FRUITFULL (FUL) and APETALA1 (AP1) function redundantly in specifying floral meristem identity but function independently in sepal and petal identity (AP1) and in proper fruit development and determinacy (FUL). Many of these functions are largely conserved in other core eudicot euAP1 and euFUL genes, but notably, the role of APETALA1 as an "A-function" (sepal and petal identity) gene is thought to be Brassicaceae specific. Understanding how functional divergence of the core eudicot duplicates occurred requires a careful examination of the function of preduplication (FUL-like) genes. Using virus-induced gene silencing, we show that FUL-like genes in opium poppy (Papaver somniferum) and California poppy (Eschscholzia californica) function in axillary meristem growth and in floral meristem and sepal identity and that they also play a key role in fruit development. Interestingly, in opium poppy, these genes also control flowering time and petal identity, suggesting that AP1/FUL homologs might have been independently recruited in petal identity. Because the FUL-like gene functional repertoire encompasses all roles previously described for the core eudicot euAP1 and euFUL genes, we postulate subfunctionalization as the functional outcome after the major AP1/FUL gene lineage duplication event.     

Analysis of PEAM4, the pea AP1 functional homologue, supports a model for AP1-like genes controlling both floral meristem and floral organ identity in different plant species

APETALA1 (AP1) and its homologue SQUAMOSA (SQUA) are key regulatory genes specifying floral meristem identity in the model plants Arabidopsis and Antirrhinum. Despite many similarities in their sequence, expression and functions, only AP1 appears to have the additional role of specifying sepal and petal identity. No true AP1/SQUA-functional homologues from any other plant species have been functionally studied in detail, therefore the question of how the different functions of AP1-like genes are conserved between species has not been addressed. We have isolated and characterized PEAM4, the AP1/SQUA-functional homologue from pea, a plant with a different floral morphology and inflorescence architecture to that of Arabidopsis or Antirrhinum. PEAM4 encodes for a polypeptide 76% identical to AP1, but lacks the C-terminal prenylation motif, common to AP1 and SQUA, that has been suggested to control the activity of AP1. Nevertheless, constitutive expression of PEAM4 caused early flowering in tobacco and Arabidopsis. In Arabidopsis, PEAM4 also caused inflorescence-to-flower transformations similar to constitutive AP1 expression, and was able to rescue the floral organ defects of the strong ap1-1 mutant. Our results suggest that the control of both floral meristem and floral organ identity by AP1 is not restricted to Arabidopsis, but is extended to species with diverse floral morphologies, such as pea.     

APETALA1 启动子驱动AtIPT4 在转基因拟南芥中表达导致花和花器官发育异常

细胞分裂素对拟南芥(Arab idopsis thal iana)花分生组织细胞的分裂和分化具有重要作用。本研究利用APETALA1(AP1)特异启动子在花分生组织和第1、2轮花器官中表达细胞分裂素合成酶(isopentyl trans ferase, IPT)基因IPT4, 研究细胞分裂素对花和花器官发育的影响。在pAP1::IPT4转基因植株中出现了花密集和花器官数目增多等现象。原位杂交和GUS组织染色结果发现, 在pAP1::IPT4转基因植株中, 花分生组织特征决定基因LEAFY (LFY)与花器官特征决定基因AP1、PISTILLATA (PI )和AGAMOUS (AG)的表达量均有不同程度的提高。研究结果表明在拟南芥中表达pAP1::IPT4影响其花和花器官的正常发育。     

APETALA1启动子驱动AtIPT4在转基因拟南芥中表达导致花和花器官发育异常

细胞分裂素对拟南芥（Arabidopsis thaliana）花分生组织细胞的分裂和分化具有重要作用。本研究利用APETALA1（AP1）特异启动子在花分生组织和第1、2轮花器官中表达细胞分裂素合成酶（isopentyl transferase,IPT）基因IPT4,研究细胞分裂素对花和花器官发育的影响。在pAP1∷IPT4转基因植株中出现了花密集和花器官数目增多等现象。原位杂交和GUS组织染色结果发现,在pAP1∷IPT4转基因植株中,花分生组织特征决定基因LEAFY（LFY）与花器官特征决定基因AP1、PISTILLATA（PI）和AGAMOUS（AG）的表达量均有不同程度的提高。研究结果表明在拟南芥中表达pAP1∷IPT4影响其花和花器官的正常发育。     

Function of the apetala-1 gene during Arabidopsis floral development.

We have characterized the floral phenotypes produced by the recessive homeotic apetala 1-1 (ap1-1) mutation in Arabidopsis. Plants homozygous for this mutation display a homeotic conversion of sepsis into brachts and the concomitant formation of floral buds in the axil of each transformed sepal. In addition, these flowers lack petals. We show that the loss of petal phenotype is due to the failure of petal primordia to be initiated. We have also constructed double mutant combinations with ap1 and other mutations affecting floral development. Based on these results, we suggest that the AP1 and the apetala 2 (AP2) genes may encode similar functions that are required to define the pattern of where floral organs arise, as well as for determinate development of the floral meristem. We propose that the AP1 and AP2 gene products act in concert with the product of the agamous (AG) locus to establish a determinate floral meristem, whereas other homeotic gene products are required for cells to differentiate correctly according to their position. These results extend the proposed role of the homeotic genes in floral development and suggest new models for the establishment of floral pattern.     

Negative regulation of the Arabidopsis homeotic gene AGAMOUS by the APETALA2 product.

We characterized the distribution of AGAMOUS (AG) RNA during early flower development in Arabidopsis. Mutations in this homeotic gene cause the transformation of stamens to petals in floral whorl 3 and of carpels to another ag flower in floral whorl 4. We found that AG RNA is present in the stamen and carpel primordia but is undetectable in sepal and petal primordia throughout early wild-type flower development, consistent with the mutant phenotype. We also analyzed the distribution of AG RNA in apetela2 (ap2) mutant flowers. AP2 is a floral homeotic gene that is necessary for the normal development of sepals and petals in floral whorls 1 and 2. In ap2 mutant flowers, AG RNA is present in the organ primordia of all floral whorls. These observations show that the expression patterns of the Arabidopsis floral homeotic genes are in part established by regulatory interactions between these genes.     

The duplicated B-class heterodimer model: whorl-specific effects and complex genetic interactions in Petunia hybrida flower development

In both Antirrhinum (Antirrhinum majus) and Arabidopsis (Arabidopsis thaliana), the floral B-function, which specifies petal and stamen development, is embedded in a heterodimer consisting of one DEFICIENS (DEF)/APETALA3 (AP3)-like and one GLOBOSA (GLO)/PISTILLATA (PI)-like MADS box protein. Here, we demonstrate that gene duplications in both the DEF/AP3 and GLO/PI lineages in Petunia hybrida (petunia) have led to a functional diversification of their respective members, which is reflected by partner specificity and whorl-specific functions among these proteins. Previously, it has been shown that mutations in PhDEF (formerly known as GREEN PETALS) only affect petal development. We have isolated insertion alleles for PhGLO1 (FLORAL BINDING PROTEIN1) and PhGLO2 (PETUNIA MADS BOX GENE2) and demonstrate unique and redundant properties of PhDEF, PhGLO1, and PhGLO2. Besides a full homeotic conversion of petals to sepals and of stamens to carpels as observed in phglo1 phglo2 and phdef phglo2 flowers, we found that gene dosage effects for several mutant combinations cause qualitative and quantitative changes in whorl 2 and 3 meristem fate, and we show that the PHDEF/PHGLO1 heterodimer controls the fusion of the stamen filaments with the petal tube. Nevertheless, when the activity of PhDEF, PhGLO1, and PhGLO2 are considered jointly, they basically appear to function as DEF/GLO does in Antirrhinum and to a lesser extent as AP3/PI in Arabidopsis. By contrast, our data suggest that the function of the fourth B-class MADS box member, the paleoAP3-type PETUNIA HYBRIDA TM6 (PhTM6) gene, differs significantly from the known euAP3-type DEF/AP3-like proteins; PhTM6 is mainly expressed in the developing stamens and ovary of wild-type flowers, whereas its expression level is upregulated in whorls 1 and 2 of an A-function floral mutant; PhTM6 is most likely not involved in petal development. The latter is consistent with the hypothesis that the evolutionary origin of the higher eudicot petal structure coincided with the appearance of the euAP3-type MADS box genes.     

<Emphasis Type="Italic">APETALA2</Emphasis> like genes from <Emphasis Type="Italic">Picea abies</Emphasis> show functional similarities to their Arabidopsis homologues

In angiosperm flower development the identity of the floral organs is determined by the A, B and C factors. Here we present the characterisation of three homologues of the A class gene APETALA2 (AP2) from the conifer Picea abies (Norway spruce), Picea abies APETALA2 LIKE1 (PaAP2L1), PaAP2L2 and PaAP2L3. Similar to AP2 these genes contain sequence motifs complementary to miRNA172 that has been shown to regulate AP2 in Arabidopsis. The genes display distinct expression patterns during plant development; in the female-cone bud PaAP2L1 and PaAP2L3 are expressed in the seed-bearing ovuliferous scale in a pattern complementary to each other, and overlapping with the expression of the C class-related gene DAL2. To study the function of PaAP2L1 and PaAP2L2 the genes were expressed in Arabidopsis. The transgenic PaAP2L2 plants were stunted and flowered later than control plants. Flowers were indeterminate and produced an excess of floral organs most severely in the two inner whorls, associated with an ectopic expression of the meristem-regulating gene WUSCHEL. No homeotic changes in floral-organ identities occurred, but in the ap2-1 mutant background PaAP2L2 was able to promote petal identity, indicating that the spruce AP2 gene has the capacity to substitute for an A class gene in Arabidopsis. In spite of the long evolutionary distance between angiosperms and gymnosperms and the fact that gymnosperms lack structures homologous to sepals and petals our data supports a functional conservation of AP2 genes among the seed plants.     

miR172 regulates stem cell fate and defines the inner boundary of APETALA3 and PISTILLATA expression domain in Arabidopsis floral meristems

In Arabidopsis, two floral homeotic genes APETALA2 (AP2) and AGAMOUS (AG) specify the identities of perianth and reproductive organs, respectively, in flower development. The two genes act antagonistically to restrict each other to their proper domains of action within the floral meristem. In addition to AG, which antagonizes AP2, miR172, a microRNA, serves as a negative regulator of AP2. In this study, we showed that AG and miR172 have distinct functions in flower development and that they largely act independently in the negative regulation of AP2. We uncovered functions of miR172-mediated repression of AP2 in the regulation of floral stem cells and in the delineation of the expression domain of another class of floral homeotic genes. Given the antiquity of miR172 in land plants, our findings have implications for the recruitment of a microRNA in the building of a flower in evolution.     

Regulation of SUP expression identifies multiple regulators involved in arabidopsis floral meristem development

During the course of flower development, floral homeotic genes are expressed in defined concentric regions of floral meristems called whorls. The SUPERMAN (SUP, also called FLO10) gene, which encodes a C2H2-type zinc finger protein, is involved in maintenance of the stamen/carpel whorl boundary (the boundary between whorl 3 and whorl 4) in Arabidopsis. Here, we show that the regulation of SUP expression in floral meristems is complex, consisting of two distinct phases, initiation and maintenance. The floral meristem identity gene LEAFY (LFY) plays a role in the initiation phase through at least two pathways, which differ from each other in the involvement of two homeotic genes, APETALA3 (AP3) and PISTILLATA (PI). AP3, PI, and another homeotic gene, AGAMOUS (AG), are further required for SUP expression in the later maintenance phase. Aside from these genes, there are other as yet unidentified genes that control both the temporal and spatial patterns of SUP expression in whorl 3 floral meristems. SUP appears to act transiently, probably functioning to trigger a genetic circuit that creates the correct position of the whorl 3/whorl 4 boundary.