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The cultivated potato (Solanum tuberosum) shares similar biology with other members of the Solanaceae, yet has features unique within the family, such as modified stems (stolons) that develop into edible tubers. To better understand potato biology, we have undertaken a survey of the potato transcriptome using expressed sequence tags (ESTs) from diverse tissues. A total of 61,940 ESTs were generated from aerial tissues, below-ground tissues, and tissues challenged with the late-blight pathogen (Phytophthora infestans). Clustering and assembly of these ESTs resulted in a total of 19,892 unique sequences with 8,741 tentative consensus sequences and 11,151 singleton ESTs. We were able to identify a putative function for 43.7% of these sequences. A number of sequences (48) were expressed throughout the libraries sampled, representing constitutively expressed sequences. Other sequences (13,068, 21%) were uniquely expressed and were detected only in a single library. Using hierarchal and k means clustering of the EST sequences, we were able to correlate changes in gene expression with major physiological events in potato biology. Using pair-wise comparisons of tuber-related tissues, we were able to associate genes with tuber initiation, dormancy, and sprouting. We also were able to identify a number of characterized as well as novel sequences that were unique to the incompatible interaction of late-blight pathogen, thereby providing a foundation for further understanding the mechanism of resistance.The Solanaceae family contains several species of agronomic importance such as tomato (Lycopersicon esculentum), potato (Solanum tuberosum), pepper (Capsicum annuum), eggplant (Solanum melongena), petunia (Petunia ϫ hybrida), and tobacco (Nicotiana tabacum). Species within the Solanaceae are highly related as evidenced by conserved sequence identity at the gene level and synteny among the homologous chromosomes (Bonierbale et al., 1988;Tanksley et al., 1992;Livingstone et al., 1999). Although members of the Solanaceae family share a number of features at the genome level, potato has a number of features that makes it unique among the Solanaceae. The most important physiological feature is the development of an edible tuber from stolons and consequently, on a global scale, potato is the fourth largest crop species grown as a food source with 300 million metric tons grown annually (http://www.cipotato.org/potato/ potato.htm). However, despite its significance as a major food source, the process of tuber development is not well understood at the molecular level. In addition, potato is susceptible to the late-blight pathogen (Phytophthora infestans), which is not only a historically significant disease that resulted in the deaths of millions of people (for review, see Schumann, 1991), but it also has recently reemerged as a significant pathogen on potato (Fry and Goodwin, 1997).The development of high-throughput sequencing technology has provided a mechanism to gain insight into genomes at the DNA and the RNA level. For assessme...

Most studies of gene expression in Plasmodium have been concerned with asexual and͞or sexual erythrocytic stages. Identification and cloning of genes expressed in the preerythrocytic stages lag far behind. We have constructed a high quality cDNA library of the Plasmodium sporozoite stage by using the rodent malaria parasite P. yoelii, an important model for malaria vaccine development. The technical obstacles associated with limited amounts of RNA material were overcome by PCR-amplifying the transcriptome before cloning. Contamination with mosquito RNA was negligible. Generation of 1,972 expressed sequence tags (EST) resulted in a total of 1,547 unique sequences, allowing insight into sporozoite gene expression. The circumsporozoite protein (CS) and the sporozoite surface protein 2 (SSP2) are well represented in the data set. A BLASTX search with all tags of the nonredundant protein database gave only 161 unique significant matches (P(N) < 10 ؊4 ), whereas 1,386 of the unique sequences represented novel sporozoite-expressed genes. We identified ESTs for three proteins that may be involved in host cell invasion and documented their expression in sporozoites. These data should facilitate our understanding of the preerythrocytic Plasmodium life cycle stages and the development of preerythrocytic vaccines.Plasmodium yoelii yoelii ͉ expressed sequence tag P rotozoan parasites of the genus Plasmodium are the causative agents of malaria, the most devastating parasitic disease in humans. The parasites occur in distinct morphological and antigenic stages as they progress through a complex life cycle, thwarting decades of efforts to develop an effective malaria vaccine. Plasmodium is transmitted via the bite of an infected Anopheles mosquito, which releases the sporozoite stage into the skin. Sporozoites enter the bloodstream and, on reaching the liver, invade hepatocytes and develop into exo-erythrocytic forms (EEF). After multiple cycles of DNA replication, the EEF contains thousands of merozoites (liver schizont) that are released into the blood stream and initiate the erythrocytic cycle (asexual blood stage) that causes the disease malaria. Changes in life cycle stages are accompanied by major changes in gene expression and therefore by major changes in antigenic composition. The form of the parasite best studied is the asexual blood stage, mainly because of its comparatively easy experimental accessibility. Therefore, most Plasmodium proteins that have been well characterized are expressed during the erythrocytic cycle, among them some major erythrocytic-stage vaccine candidates such as merozoite surface protein-1 (MSP-1) and apical membrane antigen-1 (AMA-1; ref. 1). Erythrocytic-stage vaccines are aimed at inducing an immune response that suppresses or eradicates parasite load in the blood. In contrast, preerythrocytic vaccines are aimed at eliciting an immune response that destroys the sporozoites and the EEF, thereby preventing progression of the parasite to the blood stage. The feasibility of a preerythrocytic v...