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Recent genetic and molecular studies in Arabidopsis and Antirrhinum suggest that mechanisms controlling floral development are well conserved among dicotyledonous species. To assess whether similar mechanisms also operate in more distantly related monocotyledonous species, we have begun to clone homologs of Arabidopsis floral genes from maize. Here we report the characterization of two genes, designated ZAG1 and ZAG2 (for Zea AG), that were cloned from a maize inflorescence cDNA library by low stringency hybridization with the AGAMOUS (AG) cDNA from Arabidopsis. ZAG1 encodes a putative polypeptide of 286 amino acids having 61% identity with the AGAMOUS (AG) protein. Through a stretch of 56 amino acids, constituting the MADS domain, the two proteins are identical except for two conservative amino acid substitutions. The ZAG2 protein is less similar to AG, with 49% identity overall and substantially less similarity than ZAG1 outside the well-conserved MADS domain. Like AG, ZAG1 RNA accumulates early in stamen and carpel primordia. In contrast, ZAG2 expression begins later and is restricted to developing carpels. Hybridization to genomic DNA with the full-length ZAG1 cDNA under moderately stringent conditions indicated the presence of a large family of related genes. Mapping data using maize recombinant inbreds placed ZAG1 and ZAG2 near two loci that are known to affect maize flower development, Polytypic ear (Pt) and Tassel seed4 (Ts4), respectively. The ZAG1 protein from in vitro translations binds to a consensus target site that is recognized by the AG protein. These data suggest that maize contains a homolog of the Arabidopsis floral identity gene AG and that this gene is conserved in sequence and function.
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... OsMADS13 is involved in determining ovule identity, whereas OsMADS21 does not contribute to ovule identity determination, possibly due to its low expression (Yamaguchi et al., 2006;Dreni et al., 2011). Of the two D-class genes, ZAG2 and ZMM1, identified in maize (Li et al., 2014), ZAG2 is a floral-specific gene whose expression is largely restricted to the developing ovules and the inner face of the carpels (Schmidt et al., 1993). So far, although several C-and D-class genes have been reported in different orchid species (Skipper et al., 2006;Song et al., 2006;Xu et al., 2006;Hsu et al., 2010;Wang et al., 2011;Chen et al., 2012;Salemme et al., 2013), functional analyses of these genes were mostly performed by ectopic overexpression in heterologous systems such as Arabidopsis or Nicotiana tabacum (tobacco). ...
... flowers revealed that DOAG1 was expressed in all floral organs, with the highest level in pollinia, but with the minimal level in the ovary (Fig. 1J), while DOAG2 was mainly expressed in the whole column, with the highest level in the ovary (Fig. 1K). These expression patterns are only partially similar to those observed for most AG-like genes that are expressed in the inner reproductive organs, but usually absent in sepals and petals (Kempin et al., 1993;Schmidt et al., 1993;Pnueli et al., 1994;Kang et al., 1995;Tzeng et al., 2002;Yun et al., 2004). Detectable expression of DOAG1 and DOAG2 in perianth organs, as similarly exhibited by a few AG-like genes in the basal angiosperm Illicium spp. ...
... In particular, strong 35S:DOAG1 lines displayed severely curled small leaves, stamenoid petals, and very early flowering with only three to five rosette leaves compared to wild-type plants (Fig. 3, A-E). All these phenotypes are similar to those of overexpression of AG and AG orthologs in other species (Schmidt et al., 1993;Rutledge et al., 1998;Tzeng et al., 2002). We further crossed a strong 35S:DOAG1 line (no. 1) with the Arabidopsis ag-4 mutants (Sieburth et al., 1995) to examine whether DOAG1 can compensate for the loss of AG function. ...
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Orchids (members of the Orchidaceae family) possess unique flower morphology and adaptive reproduction strategies. Although the mechanisms underlying their perianth development have been intensively studied, the molecular basis of reproductive organ development in orchids remains largely unknown. Here, we report the identification and functional characterization of two AGAMOUS (AG)-like MADS-box genes, Dendrobium Orchid AG1 (DOAG1) and DOAG2, which are putative C- and D-class genes, respectively, from the orchid Dendrobium Chao Praya Smile. Both DOAG1 and DOAG2 are highly expressed in the reproductive organ, known as the column, compared to perianth organs, while DOAG2 expression gradually increases in pace with pollination-induced ovule development and is localized in ovule primordia. Ectopic expression of DOAG1, but not DOAG2, rescues floral defects in the Arabidopsis (Arabidopsis thaliana) ag-4 mutant, including reiteration of stamenoid perianth organs in inner whorls and complete loss of carpels. Downregulation of DOAG1 and DOAG2 in orchids by artificial microRNA interference using L-methionine sulfoximine selection-based gene transformation systems shows that both genes are essential for specifying reproductive organ identity, yet exert different roles in mediating floral meristem determinacy and ovule development, respectively, in Dendrobium orchids. Notably, knockdown of DOAG1 and DOAG2 also affects perianth organ development in orchids. Our findings suggest that DOAG1 and DOAG2 not only act as evolutionarily conserved C- and D-class genes, respectively, in determining reproductive organ identity, but also play hitherto unknown roles in mediating perianth organ development in orchids.
... Genes encoding Squamosa-promoter Binding Proteins (ZmSBP10 and ZmSBP29) and NFYB4 were highly expressed in 20 mm ears and exhibited little variation in expression in response to the four levels of water deficit ( Figure 3C). Similarly, the expression of MADS box genes involved in floral organ identity, including ZAG1, ZAG2, ZMM1, and BDE (Schmidt et al., 1993;Theiben et al., 1995;Smith and Zhao, 2016) gradually increased during ear development from 5 to 50 mm, reaching a maximum level of expression in 50 mm ears. Different levels of WS had little effect on the expression of these genes ( Figure 3D). ...
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... Twenty-one genes known to be involved in regulating inflorescence and spikelet meristem development were also selected for qRT-PCR analysis (Fig. 6C, D). Genes up-regulated in bdi1 relative to 08-49 included: COM2 and its putative downstream target genes HvIDS1 (Indeterminate spikelet 1) (Chuck et al., 1998(Chuck et al., , 2007(Chuck et al., , 2008Kaplinsky et al., 2003;Lee et al., 2012) and HvLUX1 (LUX ARRHYTHMO) (Campoli et al., 2013;Poursarebani et al., 2015); and HvZAG1 (Zea agamous 1), an ortholog of maize and rice ZAG1 that controls spikelet meristem identity and determinacy (Fig. 6D) (Schmidt et al., 1993;Kaplinsky et al., 2003). One barley lateral spikelet regulator, VRS3, also showed up-regulated expression in the bdi1 mutant (Fig. 6D), but bdi1 and vrs3 mutants exhibited different defects of barley inflorescence (Bull et al., 2017;van Esse et al., 2017), indicating that this regulation may be not associated with spikelet determinacy. ...
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Barley possesses a branchless, spike-shaped inflorescence where determinate spikelets attach directly to the main axis, but the developmental mechanism of spikelet identity remains largely unknown. Here we report the functional analysis of barley gene BRANCHED AND INDETERMINATE SPIKELET 1 (BDI1), which encodes a TCP transcription factor and plays a crucial role in determining barley inflorescence architecture and spikelet development. The bdi1 mutant exhibited indeterminate spikelet meristems that continued to grow and differentiate after producing a floret meristem; some spikelet meristems at the base of the spike formed two fully developed seeds or converted to branched spikelets, producing a branched inflorescence. Map-based cloning analysis showed that this mutant has a deletion of approximate 600 kb on chromosome 5H containing three putative genes. Expression analysis and virus-induced gene silencing (VIGS) confirmed that the causative gene, BDI1, encodes a CYC/TB1 type TCP transcription factor and is highly conserved in both wild and cultivated barley. Transcriptome and regulatory network analysis demonstrated that BDI1 may integrate regulation of gene transcription cell wall modification and known T6P (trehalose-6-phosphate) homeostasis to control spikelet development. Together, our findings reveal that BDI1 represents a key regulator of inflorescence architecture and meristem determinacy in cereal crop plants.
... In Petunia hybrida, genes pMADS3 and FLORAL-BINDING PROTEIN6 (FBP6) are found to be closer homologs of AG Angenent et al., 1993;Kapoor et al., 2002). AG homologs are also isolated and characterized from tomato (TAG1) (Pnueli et al., 1994), tobacco (NAG1 Kempin et al., 1993), Brassica (BAG1), maize (ZAG1 Schmidt et al., 1993), Hyacinthus (HAG1 Li et al., 2002) and rice (OsMADS3 Kyozuka and Shimamoto, 2002). ...
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