Suitable internal control genes for qRT-PCR normalization in cotton fiber development and somatic embryogenesis

The mechanisms of cotton fiber development and somatic embryogenesis have been explored systematically with microarray and suppression subtractive hybridization. Real-time RT-PCR provides the simultaneous measurement of gene expression in many different samples, with which the data from microarray or others can be confirmed in detail. To achieve accurate and reliable gene expression results, normalization of real-time PCR data against one or several internal control genes is required, which should not fluctuate in different tissues during various stages of development. We assessed the gene expression of 7 frequently used housekeeping genes, including 18S rRNA, Histone3, UBQ7, Actin, Cyclophilin, Gbpolyubiquitin-1 and Gbpolyubiquitin-2, in a diverse set of 21 cotton samples. For fiber developmental series the expression of all housekeeping genes had the same down tendency after 17 DPA. But the expression of the AGP gene (arabinogalactan protein) that has high expression level at the later fiber development stage was up-regulated from 15 to 27 DPA. So the relative absolute quantification should be an efficient and convenient method for the fiber developmental series. The expression of nonfiber tissues series varied not so much against the fiber developmental series. And three best control genes Histone3, UBQ7 and Gbpolyubiquitin-1 have to be used in a combinated way to get better normalization.