Pineapple (Ananas comosus (L.) Merr.) is the most economically valuable crop possessing crassulacean acid metabolism (CAM), a photosynthetic carbon assimilation pathway with high water use efficiency, and the second most important tropical fruit after banana in terms of international trade. We sequenced the genomes of pineapple varieties ‘F153’ and ‘MD2’, and a wild pineapple relative A. bracteatus accession CB5. The pineapple genome has one fewer ancient whole genome duplications than sequenced grass genomes and, therefore, provides an important reference for elucidating gene content and structure in the last common ancestor of extant members of the grass family (Poaceae). Pineapple has a conserved karyotype with seven pre rho duplication chromosomes that are ancestral to extant grass karyotypes. The pineapple lineage has transitioned from C3 photosynthesis to CAM with CAM-related genes exhibiting a diel expression pattern in photosynthetic tissues using beta-carbonic anhydrase (βCA) for initial capture of CO2. Promoter regions of all three βCA genes contain a CCA1 binding site that can bind circadian core oscillators. CAM pathway genes were enriched with cis-regulatory elements including the morning (CCACAC) and evening (AAAATATC) elements associated with regulation of circadian-clock genes, providing the first link between CAM and the circadian clock regulation. Gene-interaction network analysis revealed both activation and repression of regulatory elements that control key enzymes in CAM photosynthesis, indicating that CAM evolved by reconfiguration of pathways preexisting in C3 plants. Pineapple CAM photosynthesis is the result of regulatory neofunctionalization of preexisting gene copies and not acquisition of neofunctionalized genes via whole genome or tandem gene duplication.

Independent domestication of sorghum, rice, and maize involved convergent selection for large seeds, reduced disarticulation of the mature inflorescence, and daylength-insensitive flowering. These similar phenotypes are largely determined by a small number of quantitative trait loci (QTLs) that correspond closely in the three taxa. The correspondence of these QTLs transcends 65 million years of reproductive isolation. This finding supports models of quantitative inheritance that invoke relatively few genes, obviates difficulties in map-based cloning of QTLs, and impels the comparative mapping of complex pheno-types across large evolutionary distances, such as those that separate humans from rodents and domesticated mammals.

Many major weeds rely upon vegetative dispersal by rhizomes and seed dispersal by "shattering" of the mature inflorescence. We report molecular analysis of these traits in a cross between cultivated and wild species of Sorghum that are the probable progenitors of the major weed "johnsongrass." By restriction fragment length polymorphism mapping, variation in the number of rhizomes producing above-ground shoots was associated with three quantitative trait loci (QTLs). Variation in regrowth (ratooning) after overwintering was associated with QTLs accounting for additional rhizomatous growth and with QTLs influencing tillering. Vegetative buds that become rhizomes are similar to those that become tillers-one QTL appears to influence the number of such vegetative buds available, and additional independent genes determine whether individual buds differentiate into tillers or rhizomes. DNA markers described herein facilitate cloning of genes associated with weediness, comparative study of rhizomatousness in other Poaceae, and assessment of gene flow between cultivated and weedy sorghums-a risk that constrains improvement of sorghum through biotechnology. Cloning of "weediness" genes may create opportunities for plant growth regulation, in suppressing propagation ofweeds and enhancing productivity ofmajor forage, turf, and "ratoon" crops.

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The first "complete" genetic linkage map of Sorghum section Sorghum is described, comprised of ten linkage groups putatively corresponding to the ten gametic chromosomes of S. bicolor and S. propinquum. The map includes 276 RFLP loci, predominately detected by PstI-digested S. bicolor genomic probes, segregating in 56 F2 progeny of a cross between S. bicolor and S. propinquum. Although prior cytological evidence suggests that the genomes of these species are largely homosequential, a high level of molecular divergence is evidenced by the abundant RFLP and RAPD polymorphisms, the marked deviations from Mendelian segregation in many regions of the genome, and several species-specific DNA probes. The remarkable level of DNA polymorphism between these species will facilitate development of a high-density genetic map. Further, the high level of DNA polymorphism permitted mapping of multiple loci for 21 (8.2%) DNA probes. Linkage relationships among eight (38%) of these probes suggest ancestral duplication of three genomic regions. Mapping of 13 maize genomic clones in this cross was consistent with prior results. Mapping of heterologous cDNAs from rice and oat suggests that it may be feasible to extend comparative mapping to these distantly-related species, and to ultimately generate a detailed description of chromosome rearrangements among cultivated Gramineae. Limited investigation of a small number of RFLPs showed several alleles common to S. bicolor and S. Halepense ("johnson-grass"), but few alleles common to S. propinquum and S. halepense, raising questions about the origin of S. halepense.