Sugarcane (Saccharum spp.) is a major crop for sugar and bioenergy production. Its highly polyploid, aneuploid, heterozygous, and interspecific genome poses major challenges for producing a reference sequence. We exploited colinearity with sorghum to produce a BAC-based monoploid genome sequence of sugarcane. A minimum tiling path of 4660 sugarcane BAC that best covers the gene-rich part of the sorghum genome was selected based on whole-genome profiling, sequenced, and assembled in a 382-Mb single tiling path of a high-quality sequence. A total of 25,316 protein-coding gene models are predicted, 17% of which display no colinearity with their sorghum orthologs. We show that the two species, S. officinarum and S. spontaneum, involved in modern cultivars differ by their transposable elements and by a few large chromosomal rearrangements, explaining their distinct genome size and distinct basic chromosome numbers while also suggesting that polyploidization arose in both lineages after their divergence.

The genes for two different 70-kDa heat shock protein (HSP70) homologs have been cloned and sequenced from the protozoan Giardia lambiba. On the basis of their sequence features, one of these genes corresponds to the cytoplasmic form of HSP70. The second gene, on the basis of its characteristic N-terminal hydrophobic signal sequence and C-tenal endoplasmic reticulum (ER) retention sequence (Lys-Asp-Glu-Leu), is the equivalent of ER-resident GRP78 or the Bip family of proteins. To test this hypothesis we undertook to clone HSP70 homologs from the protozoan Giardia lamblia, which lacks mitochondria (6) and which, on the basis of 16S rRNA phylogeny, constitutes the earliest diverging member within the eukaryotic lineage (7). In the present paper we describe the cloning and sequence comparison of two HSP70 homologs from G. lamblia.t One of these homologs apparently corresponds to the cytoplasmic form of the protein, whereas the other bears various characteristics of the form present in the endoplasmic reticulum (ER) (see refs. 3 and 8). Detailed comparison and phylogenetic analyses of these and other eukaryotic and prokaryotic HSP70 sequences presented here provide important insight into the origin of eukaryotic cells and of ER.

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