Submitted to: Biomed Central (BMC) Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2007
Publication Date: 5/16/2007
Citation: Taliercio, E.W., Boykin, D.L. 2007. Analysis of Gene Expression in Cotton Fiber Initials. Biomed Central (BMC) Plant Biology. 7:22. Interpretive Summary: Cotton fibers develop on the surface of the immature cotton seed. Only about 25% of cells on the seed surface develop into fibers. A method has been developed to isolate RNA from very young fibers. Genes expressed in the young fibers have been identified and deposited in a public database. Genes were identified that were expressed mainly in very young fiber. Analyses of these genes indicated that a subcellular component of the young fibers, called the endoplasmic reticulum, increased. Analysis of the genes expressed in young fiber also suggested that calcium plays a role in fiber development. Microscopic methods confirmed these observations.
Technical Abstract: Cotton (Gossypium hirsutum L.) fibers are trichomes that initiate from the ovule epidermis. A method was developed to isolate RNA from fiber 1 day after anthesis (daa). Expressed Sequence Tag (EST) libraries representing 1 dpa fibers and other cotton tissues were sequenced and analyzed. Assembly of G. hirsutum ESTs identified over 11,000 sequences not previously represented in GenBank. The high discovery rate of new sequences confirmed the importance of representing multiple tissues with normalized libraries to maximize coverage of expressed sequences. New genes identified among these ESTs were represented on microarrays. The microarrays were used to identify genes enriched in fiber initials (1 dpa fibers) and elongating fibers. Analyses of Gene Ontologies (GO) of differentially expressed genes identified a novel aspect of fiber development. GO terms associated with the “membrane” were statistically over represented among genes increased in expression in fiber initials and 10 dpa fibers. Staining ovules with a fluorescent dye confirmed an increase in Endoplasmic reticulum (ER) in fiber initials. The increase in ER occurred on the day of anthesis, persisted through 3 dpa and was absent in a fiberless mutant. Abundant ER correlated with developmental stages that require rapid production of membrane, primary cell wall and cuticle. Genes that functioned in pathways not described by the GO analyses were further examined with an emphasis on regulatory genes. Components of a Ca+2 mediated signaling path way were identified. Staining of cellular Ca+2 indicated that fiber initials had more Ca+2 than other ovule cells supporting a role for Ca+2 in fiber development.