Analysis of cDNA libraries from developing seeds of guar (Cyamopsis tetragonoloba (L.) Taub)

A database of 16,476 guar seed ESTs was constructed, with 8,163 and 8,313 ESTs derived from cDNA libraries I and II, respectively. Library I was constructed from seeds at an early developmental stage (15–25 days after flowering, DAF), and library II from seeds at 30–40 DAF. Quite different sets of genes were represented in these two libraries. Approximately 27% of the clones were not similar to known sequences, suggesting that these ESTs represent novel genes or may represent non-coding RNA. The high flux of energy into carbohydrate and storage protein synthesis in guar seeds was reflected by a high representation of genes annotated as involved in signal transduction, carbohydrate metabolism, chaperone and proteolytic processes, and translation and ribosome structure. Guar unigenes involved in galactomannan metabolism were identified. Among the seed storage proteins, the most abundant contig represented a conglutin accounting for 3.7% of the total ESTs from both libraries.The present EST collection and its annotation provide a resource for understanding guar seed biology and galactomannan metabolism.Guar, or clusterbean (Cyamopsis tetragonoloba (L.) Taub), is a drought-tolerant annual legume, which originated in the India-Pakistan area, and was introduced into the United States in 1903 [1]. Unlike the seeds of other legumes, guar seeds have a large endosperm, accounting for 42% of seed weight [2]. The predominant portion of the endosperm is mucilage or gum (guar gum), which forms a viscous gel in cold water. Approximately 80–85% of the gum is a galactomannan, consisting of a linear (1→4)-β-linked D-mannan backbone with single-unit, (1→6)-linked, α-D-galactopyranosyl side chains [3-6]. The galactomannan is in the form of non-ionic polydisperse rod-shaped polymers consisting of about 10,000 residues, which accumulate in the primary cell walls of the endosperm [7].Galactomannans from various leguminous species have different degrees of galactose substitution. Low galac