dictyNews Electronic Edition Volume 39, number 22 August 2, 2013 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu or by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= Biological soliton in multicellular movement Hidekazu Kuwayama, Shuji Ishida Scientific Reports, 3, Article number: 2272 Solitons have been observed in various physical phenomena. Here, we show that the distinct characteristics of solitons are present in the mass cell movement of non-chemotactic mutants of the cellular slime mould Dictyostelium discoideum. During starvation, D. discoideum forms multicellular structures that differentiate into spore or stalk cells and, eventually, a fruiting body. Non-chemotactic mutant cells do not form multicellular structures; however, they do undergo mass cell movement in the form of a pulsatile soliton-like structure (SLS). We also found that SLS induction is mediated by adhesive cell-cell i nteractions. These observations provide novel insights into the mechanisms of biological solitons in multicellular movement. Submitted by Hidekazu Kuwayama [hidekuwayama@biol.tsukuba.ac.jp] --------------------------------------------------------------------------- A Unique Mitochondrial Transcription Factor B Protein in Dictyostelium discoideum. Sam Manna (1), Phuong Le (2), Christian Barth (1) (1) Department of Microbiology, La Trobe University, Melbourne, Victoria, Australia, (2) Tokyo Metropolitan University, Department of Biological Science, Tokyo, Japan PLoS ONE 8(7): e70614. doi:10.1371/journal.pone.0070614 Unlike their bacteriophage homologs, mitochondrial RNA polymerases require the assistance of transcription factors in order to transcribe mitochondrial DNA efficiently. The transcription factor A family has been shown to be important for transcription of the human mitochondrial DNA, with some of its regulatory activity located in its extended C-terminal tail. The mitochondrial transcription factor B family often has functions not only in transcription, but also in mitochondrial rRNA modification, a hallmark of its alpha-proteobacterial origin. We have identified and characterised a mitochondrial transcription factor B homolog in the soil dwelling cellular slime mould Dictyostelium discoideum, an organism widely established as a model for studying eukaryotic cell biology. Using in bacterio functional assays, we demonstrate that the mitochondrial transcription factor B homolog not only functions as a mitochondrial transcription factor, but that it also has a role in rRNA methylation. Additionally, we show that the transcriptional activation properties of the D. discoideum protein are located in its extended C-terminal tail, a feature not seen before in the mitochondrial transcription factor B family, but reminiscent of the human mitochondrial transcription factor A. This report contributes to our current understanding of the complexities of mitochondrial transcription, and its evolution in eukaryotes. Submitted by Christian Barth [c.barth@latrobe.edu.au] --------------------------------------------------------------------------- Protein phosphatase 4 is involved in the late development of Dictyostelium discoideum Ichiro Kamei, Kozo Takamoto, Naoya Sakuragi, Eiji Tanesaka, Motonobu Yoshida Open J. Molecu. Integra. Physiol., in press A cDNA clone SSJ337 (accession no. AF161253) of 1,230 bp, encoding a catalytic subunit of protein phosphatase 4, was selected as one of the clones expressed specifically in prestalk cells from a cDNA library of D. discoideum slugs. Cells transformed with a knockout construct of SSJ337 showed an aberrant and tiny fruiting-body formation with a short stalk. A knockout mutant, SSJ337KO was allowed to develop much slower than a wild-type AX2 after the post-aggregation stage. This suggested that the SSJ337 cDNA clone played an important role especially in the late development of Dictyostelium discoideum. Results from Northern blotting analysis showed that transcripts for SSJ337 were accumulated at 16 h to 24 h after starvation began. Submitted by Motonobu Yoshida [yoshida_m@nara.kindai.ac.jp] --------------------------------------------------------------------------- Social amoeba farmers carry defensive symbionts to protect and privatize their crops Debra A. Brock (1), Silven Read (2), Alona Bozhchenko (2), David C. Queller (1}, and Joan E. Strassmann (1 ) (1) Department of Biology, Washington University at St. Louis, St. Louis, Missouri 63130, USA (2) Department of Ecology and Evolutionary Biology, Rice University, Houston, Texas 77005, USA Nature Communications, in press Agricultural crops are investments that can be exploited by others. Farmer clones of the social amoeba Dictyostelium discoideum carry bacteria to seed out new food populations but they also carry other non-food bacteria such as Burkholderia spp. Here we demonstrate that these farmer-carried Burkholderia inhibit the growth of non-farmer D. discoideum clones that could exploit the farmerÕs crops. Using supernatants, we show that inhibition is due to molecules secreted by Burkholderia. When farmer and non-farmer amoebae are mixed together at various frequencies and allowed to complete the social stage, the ability of non-farmers to produce spores falls rapidly with an increase in the percentage of farmers with their defensive symbionts, but conversely, farmer spore production is unaffected by the frequency of farmers. Our results suggest that successful farming is a complex evolutionary a daptation, because it requires additional strategies, like recruiting third parties, to effectively defend and privatize crops. Submitted by David Queller [queller@wustl.edu] --------------------------------------------------------------------------- A bacterial symbiont is converted from an inedible producer of beneficial molecules into food by a single mutation in the gacA gene Pierre Stallforth (1), Debra A. Brock (2), Alexandra M. Cantley (1), Xiangjun Tian (2), David C. Queller (2), Joan E. Strassmann (2), Jon Clardy (1) (1) Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115 (2) Department of Biology, Washington University in St. Louis, St. Louis, MO 63130 PNAS , in press; available online http://www.pnas.org.ezproxy.rice.edu/content/early/2013/07/26/1308199110.abstract Stable multipartite mutualistic associations require that all partners benefit. We show that a single mutational step is sufficient to turn a symbiotic bacterium from an inedible but host-beneficial secondary metabolite producer into a host food source. The bacteriaÕs host is a ÒfarmerÓ clone of the social amoeba Dictyostelium discoideum that carries and disperses bacteria during its spore stage. Associated with the farmer are two strains of Pseudomonas fluorescens, only one of which serves as a food source. The other strain produces diffusible s mall molecules: pyrrolnitrin, a known antifungal agent, and a chromene that potently enhances the farmerÕs spore production and depresses a nonfarmerÕs spore production. Genome sequence and phylogenetic analyses identify a derived point mutation in the food strain that generates a premature stop codon in a global activator (gacA), encoding the response regulator of a two-component regulatory system. Generation of a knockout mutant of this regulatory gene in the nonfood bacterial strain altered its secondary metabolite profile to match that of the food strain, and also, independently, converted it into a food source. These results suggest that a single mutation in an inedible ancestral strain that served a protective role converted it to a ÒdomesticatedÓ food source. Submitted by David Queller [queller@wustl.edu] --------------------------------------------------------------------------- Kin Recognition Protects Cooperators Against Cheaters Hsing-I Ho, Shigenori Hirose, Adam Kuspa, and Gad Shaulsky Baylor College of Medicine, Houston, TX 77030 Current Biology, in press The evolution of sociality and altruism is enigmatic because cooperators are constantly threatened by cheaters who benefit from cooperation without incurring its full cost. Kin recognition is the ability to recognize and cooperate with genetically close relatives. It has also been proposed as a potential mechanism that limits cheating, but there has been no direct experimental support for that possibility. Here we show that kin recognition protects cooperators against cheaters. The social amoebae Dictyostelium discoideum cooperate by forming multicellular aggregates that develop into fruiting bodies of viable spores and dead stalk cells. Cheaters preferentially differentiate into spores while their victims die as stalk cells in chimeric aggregates. We engineered syngeneic cheaters and victims that differed only in their kin-recognition genes, tgrB1 and tgrC1, and in a single cheater allele and found that the victims escaped exploitation by different types of nonkin cheaters. This protection depends on kin-recognition-mediated segregation because it is compromised when we disrupt strain segregation. These findings provide direct evidence for the role of kin recognition in cheater control and suggest a mechanism for the maintenance of stable cooperative systems. Submitted by Gad Shaulsky [gadi@bcm.edu] --------------------------------------------------------------------------- The cytohesin paralog Sec7 of Dictyostelium discoideum is required for phagocytosis and cell motility Mueller, R., Herr, C., Sukumaran, S. K., Omosigho, N. N., Plomann, M., Riyahi, T. Y., Stumpf, M., Swaminathan, K., Tsangarides, M., Yiannakou, K., Blau-Wasser, R., Gallinger, C., Schleicher ,M., Kolanus, W., Noegel A. A. Cell Communication and Signaling , in press Background: Dictyostelium harbors several paralogous Sec7 genes that encode members of three subfamilies of the Sec7 superfamily of guanine nucleotide exchange factors. One of them is the cytohesin family represented by three members in D. discoideum, SecG, Sec7 and a further protein distinguished by several transmembrane domains. Cytohesins are characterized by a Sec7-PH tandem domain and have roles in cell adhesion and migration. Results: We study here Sec7. In vitro its PH domain bound preferentially to phosphatidylinositol 3,4-bisphosphate (PI(3,4)P2), phosphatidylinositol 4,5- bisphosphate (PI(4,5)P2) and phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3). When following the distribution of GFP-Sec7 in vivo we observed the protein in the cytosol and at the plasma membrane. Strikingly, when cells formed pseudopods, macropinosomes or phagosomes, GFP-Sec7 was conspicuously absent from areas of the plasma membrane which were involved in these processes. Mutant cells lacking Sec7 exhibited an impaired phagocytosis and showed significantly reduced speed and less persistence during migration. cellular properties associated with mammalian cytohesins like cell-cell and cell-substratum adhesion were not altered. Proteins with roles in membrane trafficking and signal transduction have been identified as putative interaction partners consistent with the data obtained from mutant analysis. Conclusions: Sec7 is a cytosolic component and is associated with the plasma membrane in a pattern distinctly different from the accumulation of PI(3,4,5)P3. Mutant analysis reveals that loss of the protein affects cellular processes that involve membrane flow and the actin cytoskeleton. Submitted by Angelika Noegel [noegel@uni-koeln.de] ============================================================== [End dictyNews, volume 39, number 21]