Your question is very interesting. When we go through Genetics, there is always a lot to read, a lot to learn, and a lot to ask. I am not an expert in this field, but I have been doing some research on the Web to try to answer your question.

The fiber cells of cotton (Gossypium hirsutum L.) represent a single cell type that undergoes a period of very rapid elongation. According to my results from the Web, there are two types of family genes (cotton celA1 and celA2) which are expressed at higher levels in developing cotton fibers. Plant cell expansion occurs through the interaction of multiple influences, including cell wall-yield properties; the opposing force of turgid pressure; the biosynthesis of new membrane lipids, cell wall components, and proteins; and proper trafficking of these newly synthesized materials to their final cellular destination.

In animals, the small GTP-binding proteins, Rac and Rho, of the R's super-family, participate in the signal transduction pathway that regulates the organization of the actin- cytoskeleton. In a report about Genetics of plants, some researchers characterized two distinct cDNA clones isolated from a cotton fiber cDNA library that code for homolog of animal Rac proteins. They designate that homolog as Rac13 and Rac9. The gene for Rac13 shows highly enhanced expression in developing cotton fibers, with maximal expression occurring at the time of transition between primary and secondary wall synthesis.