Apomixis, the clonal formation of seeds, is a rare yet widely distributed trait in flowering plants. We have isolated the PARTHENOGENESIS (PAR) gene from apomictic dandelion that triggers embryo development in unfertilized egg cells. PAR encodes a K2-2 zinc finger, EAR-domain protein. Unlike the recessive sexual alleles, the dominant PAR allele is expressed in egg cells and has a miniature inverted-repeat transposable element (MITE) transposon insertion in the promoter. The MITE-containing promoter can invoke a homologous gene from sexual lettuce to complement dandelion LOSS OF PARTHENOGENESIS mutants. A similar MITE is also present in the promoter of the PAR gene in apomictic forms of hawkweed, suggesting a case of parallel evolution. Heterologous expression of dandelion PAR in lettuce egg cells induced haploid embryo-like structures in the absence of fertilization. Sexual PAR alleles are expressed in pollen, suggesting that the gene product releases a block on embryogenesis after fertilization in sexual species while in apomictic species PAR expression triggers embryogenesis in the absence of fertilization.

Apomixis in the common dandelion (Taraxacum officinale) consists of three developmental components: diplospory (apomeiosis), parthenogenesis, and autonomous endosperm development. The genetic basis of diplospory, which is inherited as a single dominant factor, has been previously elucidated. To uncover the genetic basis of the remaining components, a cross between a diploid sexual seed parent and a triploid apomictic pollen donor was made. The resulting 95 triploid progeny plants were genotyped with co-dominant simple-sequence repeat (SSR) markers and phenotyped for apomixis as a whole and for the individual apomixis components using Nomarski Differential Interference Contrast (DIC) microscopy of cleared ovules and seed flow cytometry. From this, a new SSR marker allele was discovered that was closely linked to parthenogenesis and unlinked to diplospory. The segregation of apomixis as a whole does not differ significantly from a three-locus model, with diplospory and parthenogenesis segregating as unlinked dominant loci. Autonomous endosperm is regularly present without parthenogenesis, suggesting that the parthenogenesis locus does not also control endosperm formation. However, the high recovery of autonomous endosperm is inconsistent with this phenotype segregating as the third dominant locus. These results highlight the genetic complexity underlying apomixis in the dandelion and underline the challenge of introducing autonomous apomixis into sexual crops.

Introduction of apomixis, asexual reproduction through seeds, into crop species has the potential to dramatically transform plant breeding. A new study demonstrates that traits can be stably transferred between generations in newly produced apomictic lines, and heralds a breeding revolution needed to increase food production for the growing planet.

The localization capability of human mesenchymal stem cell (hMSCs) to tumors offers an attractive possibility as a cellular vehicle delivery route of immunotherapeutic genes. The RheoSwitch Therapeutic System® (RTS®) platform allows for regulated expression following exposure and withdrawal of activator ligand (AL) veledimex (also known as INXN-1001). In this study, we first evaluated RTS® regulated IL-12 expression from adenovirally transduced hMSC to generate a genetically modified hMSC (GM-hMSC) that could be used as a vehicle for gene delivery with the added benefit of migration potential to the tumor for therapy. Following establishment of the cultures in vitro, hMSCs were phentoypically similar following adenoviral vector transduction to mock transduced hMSCs based upon marker expression, characterized by flow cytometry. Levels of human and mouse IL-12 secreted from the hMSCs transduced with Ad-RTS-hIL-12 and Ad-RTS-mIL-12 respectively, directly correlated with the viral vector doses (1K-20K vp/cell). hMSC transduction efficiency was ∼90% with an MOI of 20K/cell. In addition, sustained cell levels of IL-12 expression were observed up to 53 days following transduction when maintained in the presence of veledimex. Furthermore, cycling of in vitro exposure periods between veledimex and excipient demonstrated the ability for on/off/on and off/on/off kinetics of IL-12 expression by transduced hMSCs. We then expanded on the concept of RTS® regulated gene expression in GM-hMSCs using multigenic plasmid constructs that simultaneously expressed three immunomodulators - human IL-12, human IFNα, and a CTLA4 decoy - in single, dual or triple combinations. Transient transfection of the multieffector plasmid using the AMAXA nucleofector system resulted in RTS® regulated concomitant expression of all three effectors. hIL-12 and hIFNα were found to be fully bio-functional in their respective cell based functional assays; - hIL-12 increased IFNγ secretion from NK92 cells, hIFNα enhanced STAT1 reporter activity, and the CTLA4 decoy functional assay is in progress. Taken together, these in vitro studies highlight the potential use of MSCs for tumor-targeted delivery of single or multiple RTS® regulated cancer immunotherapies. Altogether, use of these novel regulated immunotherapeutic approaches could potentially be translated into an effective clinical regimen for a variety of cancers. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C234. Citation Format: Tim Chan, Anjali Prabhu, Anissa Elayadi, Lindsay Williams, Vernon Dailey, Kristi Elliot, Tracey Snipas, Jonathan Carson, Jonathan Lewis, Stephen Schauer, Daniel Bednarik, Jayson M. Rieger, Laurent M. Humeau, Thomas R. Reed. Regulated immunomodulators expression using the RheoSwitch Therapeutic System® platform in human mesenchymal stem cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C234.

Abstract The ubiquity and importance of short duplex RNAs, termed microRNA (miRNA), for normal development in higher eukaryotes are becoming increasingly clear. We had previously shown that reduction-of-function mutations in Arabidopsis thaliana DCL1 (DICER-LIKE1) gene, affecting the nucleus-localized protein that produces 19-25 nucleotides long miRNA species from longer double stranded RNA precursors, cause a delay in flowering by prolonging the period of juvenile organ development. Here we show that DCL1 transcription is increased at the critical phase of juvenile to reproductive developmental transition, and that DCL1 protein is localized in meristematic cells of the shoot, inflorescence and flowering meristem. DCL1 protein is also expressed in the ovule funiculus, ovule integuments, and in early but not late embryo. Genetic analysis revealed that DCL1 exerts its effect along the same pathway that involves the floral pathway integrator gene LEAFY. Results are most consistent with the idea that DCL1 protein is required in the shoot apical meristem to prevent uncontrolled proliferation of meristematic cells. The expression of DCL1 protein in the early embryo may be either via the transmission of DCL1 mRNA through the female gametophyte, as suggested from the sporophytic maternal effect of dcl1-8 on early embryo development, or from DCL1 mRNA synthesized in early embryo cells off the maternally transmitted allele. The requirement of an active maternally transmitted allele of DCL1 for normal early embryo development, and the presence of DCL1 protein in the early embryo, together suggest that the synthesis of miRNA in early embryo cells is critical for development, but does not rule out potential maternal contribution of miRNA or its precursor molecules into the embryo. (Manuscript was prepared on February 2, 2007, and has been unaltered since)

Abstract Over the past decade, immunotherapies have emerged as prominent means to fight cancer. It is currently well accepted that combining multiple immunomodulatory therapeutic modalities will likely have a deeper impact in promoting cancer remission than monotherapies. Toward the development of a tri-immuno-therapeutic approach, we evaluated the feasibility and expression potency of multigenic plasmid constructs that simultaneously expressed three immunomodulators - human IL-12, human IFNα, and a CTLA4 decoy - in single, dual or triple combinations. In all constructs, the three effectors were expressed under the control of Intrexon's RheoSwitch Therapeutic System® (RTS®) activated by an orally available small molecule activator ligand (AL), veledimex (also known as INXN-1001). Expression of the three genes of interest (GOI) was driven by distinct RTS® inducible promoters, which allow for conditional gene expression following oral treatment with veledimex. Seven plasmids were constructed; three encoding for each GOI alone, three containing a combination of two GOIs; and one plasmid expressing all three GOIs. Expression of each GOI from each plasmid was evaluated in vitro in HT1080 and HEK293T cells for expression and function, and in vivo following administration through a single IM injection and electroporation into mice pre-exposed to the AL. Three days post IM/EP and daily oral treatment with veledimex, animals were bled and sera were evaluated for the single or concomitant expression and function of the encoded GOIs. Transient transfection and in vivo electroporation of the single and multi-effector plasmids yielded increased levels of hIL-12, hIFNα, and the CTLA4 decoy, when combined with veledimex. In contrast, no expression was seen in cell culture supernatants or sera in the absence of the activator ligand. Importantly, all three effectors, expressed from single plasmids were functionally active in cell based assays - hIL-12 increased IFNγ secretion from NK92 cells, hIFNα enhanced STAT1 activation, and the CTLA4 decoy blocked CD80 binding to CTLA4. Taken together, these results show for the first time the feasibility of systemic expression of three distinct immune effectors from a single RTS® regulated multigenic construct in mice. The in vivo studies also highlight the potential use of an ECB to generate therapeutics for tumor-targeted delivery of single or multiple RTS® regulated cancer immunotherapies. Altogether, use of these novel regulated immunotherapeutic approaches could potentially be translated into an effective clinical regimen for a variety of cancers. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B127. Citation Format: Pooja Agarwal, Stephen Schauer, Xiaohong Ma, Jacques Plummer, Tim Chan, Lindsay Williams, Michele Kaloss, John A. Barrett, Richard Einstein, Laurent M. Humeau, Thomas R. Reed. Pharmacodynamics and functionality of RheoSwitch® regulated immunomodulatory proteins, expressed from a multigenic embedded cellular bioreactor following intramuscular electroporation in mice. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B127.

The screening of enhancer detector lines in Arabidopsis thaliana has identified genes that are specifically expressed in the sporophytic tissue of the ovule. One such gene is the MADS-domain transcription factor AGAMOUS-LIKE6 (AGL6), which is expressed asymmetrically in the endothelial layer of the ovule, adjacent to the developing haploid female gametophyte. Transcription of AGL6 is regulated at multiple stages of development by enhancer and silencer elements located in both the upstream regulatory region and the large first intron. These include a bipartite enhancer, which requires elements in both the upstream regulatory region and the first intron, active in the endothelium. Transcription of the AGL13 locus, which encodes the other member of the AGL6 subfamily in Arabidopsis, is also regulated by elements located in the upstream regulatory region and in the first intron. There is, however, no overlapping expression of AGL6 and AGL13 except in the chalaza of the developing ovule, as was shown using a dual gene reporter system. Phylogenetic shadowing of the first intron of AGL6 and AGL13 homologs from other Brassicaceae identified four regions of conservation that probably contain the binding sites of transcriptional regulators, three of which are conserved outside Brassicaceae. Further phylogenetic analysis using the protein-encoding domains of AGL6 and AGL13 revealed that the MADS DNA-binding domain shows considerable divergence. Together, these results suggest that AGL6 and AGL13 show signs of subfunctionalization, with divergent expression patterns, regulatory sequences and possibly functions.

The importance of maternal cells in controlling early embryogenesis is well understood in animal development, yet in plants the precise role of maternal cells in embryogenesis is unclear. We demonstrated previously that maternal activity of the SIN1 (SHORT INTEGUMENTS1) gene of Arabidopsis is essential for embryo pattern formation and viability, and that its postembryonic activity is required for several processes in reproductive development, including flowering time control and ovule morphogenesis. Here, we report the cloning of SIN1, and demonstrate its identity to the CAF (CARPEL FACTORY) gene important for normal flower morphogenesis and to the SUS1 (SUSPENSOR1) gene essential for embryogenesis. SIN1/SUS1/CAF has sequence similarity to the Drosophila melanogaster gene Dicer, which encodes a multidomain ribonuclease specific for double-stranded RNA, first identified by its role in RNA silencing. The Dicer protein is essential for temporal control of development in animals, through the processing of small RNA hairpins that in turn inhibit the translation of target mRNAs. Structural modeling of the wild-type and sin1 mutant proteins indicates that the RNA helicase domain of SIN1/SUS1/CAF is important for function. The mRNA was detected in floral meristems, ovules, and early embryos, consistent with the mutant phenotypes. A 3.3-kb region 5' of the SIN1/SUS1/CAF gene shows asymmetric parent-of-origin activity in the embryo: It confers transcriptional activation of a reporter gene in early embryos only when transmitted through the maternal gamete. These results suggest that maternal SIN1/SUS1/CAF functions early in Arabidopsis development, presumably through posttranscriptional regulation of specific mRNA molecules.

Genetic studies of embryo, ovule and flower development in Arabidopsis thaliana have led to the independent isolation of different mutant alleles of a single gene (SIN1/SUS1/CAF, now renamed DCL1) that encodes a complex RNA-processing enzyme. DCL1 shows similarity to the Dicer group of genes, which are required for RNA silencing in Drosophila and Caenorhabditis. These recent findings identify a novel but conserved mechanism of post-transcriptional gene regulation that is important for development in eukaryotes.

The importance of maternal cells in controlling early embryogenesis is well understood in animal development, yet in plants the precise role of maternal cells in embryogenesis is unclear. We demonstrated previously that maternal activity of theSIN1 (SHORT INTEGUMENTS1) gene of Arabidopsis is essential for embryo pattern formation and viability, and that its postembryonic activity is required for several processes in reproductive development, including flowering time control and ovule morphogenesis. Here, we report the cloning of SIN1, and demonstrate its identity to the CAF (CARPEL FACTORY) gene important for normal flower morphogenesis and to the SUS1 (SUSPENSOR1) gene essential for embryogenesis.SIN1/SUS1/CAF has sequence similarity to the Drosophila melanogaster geneDicer, which encodes a multidomain ribonuclease specific for double-stranded RNA, first identified by its role in RNA silencing. The Dicer protein is essential for temporal control of development in animals, through the processing of small RNA hairpins that in turn inhibit the translation of target mRNAs. Structural modeling of the wild-type and sin1 mutant proteins indicates that the RNA helicase domain of SIN1/SUS1/CAF is important for function. The mRNA was detected in floral meristems, ovules, and early embryos, consistent with the mutant phenotypes. A 3.3-kb region 5′ of theSIN1/SUS1/CAF gene shows asymmetric parent-of-origin activity in the embryo: It confers transcriptional activation of a reporter gene in early embryos only when transmitted through the maternal gamete. These results suggest that maternal SIN1/SUS1/CAF functions early in Arabidopsis development, presumably through posttranscriptional regulation of specific mRNA molecules.

Stephen E. Schauer, Teresa A. Golden, Delwin S. Merchant, Biranchi N. Patra, Jean D. Lang, Sumita Ray, Bulbul Chakravarti, Deb Chakravarti, and Animesh Ray Department of Biology, University of Rochester, Rochester, NY 14627, USA and Keck Graduate Institute, 535 Watson Drive, Claremont, CA 91711, USA Address communication to: Animesh Ray, Keck Graduate Institute, Claremont, CA 91711; Phone: (909) 607 9729. Email: aray@kgi.edu