The present invention provides plant fiber expansion (FE) genes that encode FE polypeptides, such as phosphoenol pyruvate carboxylase (PEPcase), expansin, endoglucanase, xyloglucan endoglycosyltransferase (XET), and pectin methyl esterase (PME). The invention further provides fiber-specific promoters. Still further, the invention provides molecular strategies for modulating fiber quality and yield in fiber producing plants by modulating expression of FE genes or mutant forms of FE genes.