This Week in PNAS
INAUGURAL ARTICLE, ANTHROPOLOGY
Final days of Cerro Baúl colony
Michael Moseley et al. analyzed archaeological data from Wari settlement of the Cerro Baúl mesa in southern Peru and conclude that the Wari elite abandoned their colony in anno Domini 1000 with elaborate ceremonies that included brewing, drinking, feasting, vessel smashing, and building burning. Monumental ruins atop this 600-m promontory were uncovered in the 1970s, but the purpose of the settlement has been unclear. Moseley et al. suggest that the Wari empire established an elaborate settlement on Cerro Baúl to serve an embassy-like delegation of nobles and attendant personnel in negotiation with the Tiwanaku state to the south. The colony included agglutinated high-walled compounds, a lavish residential palace, and a brewery capable of producing 1,800-liter batches of chicha, an alcoholic beverage of fermented corn or berries. The structures were abandoned swiftly, the authors say, with the brewery probably the last to be evacuated. The evidence supports a scenario of a planned closure that started with brewing a final batch of chicha and involved feasting and drinking. The evacuation ceremony culminated with setting the brewery on fire and the Wari paramount lords sacrificing their ornate drinking vessels by dashing them to the ground in the fire. — R.N.
Cerro Baúl mesa in southern Peru.
“Burning down the brewery: Establishing and evacuating an ancient imperial colony at Cerro Baúl, Peru” by Michael E. Moseley, Donna J. Nash, Patrick Ryan Williams, Susan D. deFrance, Ana Miranda, and Mario Ruales (see pages 17264–17271)
PHYSICS
Molecular motors drive cooperative cargo transport
Stefan Klumpp and Reinhard Lipowsky calculate the dynamic properties of cooperative molecular motors in intracellular transport, providing testable predictions in the study of protein motors, such as kinesin. To date, protein motors have mostly been studied in vitro as single units, although in vivo they work together. Kinesins release from a filament after a finite number of work cycles but can reattach, implying that the number of pulling motors is not fixed but varies with time. Klumpp and Lipowsky studied how the forces and speeds produced vary with the number of kinesins on the strand. Their mathematical modeling showed that more motors yield longer distances and, in the presence of a load force, more rapid speeds. In their calculations, seven or eight kinesins can tow a load up to 1 cm. The model also explains why vesicles have been observed to move at integer multiples of the slowest speed, and it may thus help elucidate the transport properties of intracellular cargoes, such as vesicles and cellular organelles. Predictions concerning force–velocity relationships, walking distances, and distribution of instantaneous velocities can be derived from the modeling, according to the authors, and should all be measurable in the near future. — P.D.
Cargo particle, such as a vesicle (blue), pulled by up to four molecular motors.
“Cooperative cargo transport by several molecular motors” by Stefan Klumpp and Reinhard Lipowsky (see pages 17284–17289)
EVOLUTION
Regional clonal population structure of malaria agent
F. G. Razakandrainibe et al. report that the population structure of Plasmodium falciparum in Kenya, where malignant malaria is perennial and intense, appears to be “clonal,” and not at all panmictic (randomly mated within population). The authors studied the genetic composition of P. falciparum in the midgut oocysts of the mosquito vector, where diploid genotypes can be determined. Genetic polymorphisms were investigated at seven microsatellite loci located on five chromosomes. A total of 613 oocysts in 145 mosquito samples was assayed from 11 locations in Kenya. Considerable allelic variation and inbreeding were found, due partly to self-fertilization and nonrandom genotype distribution of oocysts among mosquito guts. Linkage disequilibrium was statistically significant for all pairwise comparisons between loci, which is consistent with strong deviation from panmixia and the consequent reproduction of genomes as clones without recombination between gene loci. Razakandrainibe et al. say that, although a variety of population structures may prevail in different regions, researchers should consider that a clonal population structure of P. falciparum may prevail in regions of perennial transmission as well as in regions of low infectivity. — R.N.
P. falciparum oocysts.
“`Clonal' population structure of the malaria agent Plasmodium falciparum in high-infection regions” by F. G. Razakandrainibe, P. Durand, J. C. Koella, T. De Meeüs, F. Rousset, F. J. Ayala, and F. Renaud (see pages 17388–17393)
PLANT BIOLOGY
Rice-based peptide immunotherapy for allergy
Hidenori Takagi et al. report on the development of an edible vaccine based on transgenic rice expressing pollen allergen peptides. The rice plants expressed mouse dominant epitope peptides of Cry j I and Cry j II allergens of Japanese cedar pollen as a fusion protein with the soybean seed storage protein glycinin. The fusion protein was expressed at a level of 0.5% of total seed protein. Compared with control groups fed nothing or only unmodified rice, mice fed the transgenic rice seeds daily for 4 weeks showed greater oral tolerance against the cedar pollen allergen. Tolerance was associated with decreased production of T helper 2 cytokines (IL-4, IL-5, and IL-13). Allergen-specific serum IgE and IgG antibody, CD4+ cell proliferative responses, and histamine release from the treated mice were also inhibited. Clinical symptoms of allergy were suppressed, as assessed by an experimental sneezing mouse model. The seed-expression system may have advantages for the production of recombinant proteins, such as simplicity of administration, low risk of contamination with animal pathogens, low cost of production, and long storage at room temperature, the authors say. The results suggest the potential of transgenic rice seeds for oral peptide immunotherapy to pollen allergens. — R.N.
Transformation plasmid of allergen peptide fusion protein.
“A rice-based edible vaccine expressing multiple T cell epitopes induces oral tolerance for inhibition of Th2-mediated IgE responses” by Hidenori Takagi, Takachika Hiroi, Lijun Yang, Yoshifumi Tada, Yoshikazu Yuki, Kaoru Takamura, Ryotaro Ishimitsu, Hideyuki Kawauchi, Hiroshi Kiyono, and Fumio Takaiwa (see pages 17525–17530)
PLANT BIOLOGY
Arabidopsis seed size genes identified
Ming Luo et al. have identified two genes, MINI3 and IKU2, in a pathway that regulates seed size in Arabidopsis. Previous research has shown that the FIS loci control endosperm growth and seed size in both dicots, like Arabidopsis, and monocots, such as maize. The authors recovered two Arabidopsis mutants that produced seeds significantly smaller than the parental seeds. Forty-eight hours after pollination, the mutant seeds were of comparable size to controls, but by 72 hours, the ovules of both mini3 and iku2 plants had a reduced number of endosperm nuclei. IKU2 was localized to chromosome 3, and MINI3 was localized to chromosome 1. IKU2 encodes a leucine-rich repeat kinase, and MINI3 is predicted to encode a WRKY transcription factor. MINI3 expression was observed in the male gametophyte, fertilized ovule, embryo, and endosperm. No difference in expression was observed whether the gene was delivered as the paternal or maternal allele. IKU2 was also present in the endosperm nuclei, though with lesser expression. Both MINI3 and IKU2 had a lower expression level in an iku2 mutant background, which has been shown to decrease endosperm growth. IKU2 expression was reduced in the mini3 background, but MINI3 expression levels were unchanged in the iku2 mutant. These three genes appear to operate in a unique pathway controlling seed development. — F.A.
Normal and mutant Arabidopsis seeds with lesions in MINI3 and IKU2 genes.
“MINISEED3 (MINI3), a WRKY family gene, and HAIKU2 (IKU2), a leucine-rich repeat (LRR) KINASE gene, are regulators of seed size in Arabidopsis” by Ming Luo, Elizabeth S. Dennis, Frederic Berger, William James Peacock, and Abed Chaudhury (see pages 17531–17536)
