TITLE : Cellulose Synthase Catalytic Subunit ( Cesa ) Genes Associated 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 With Primary or Secondary Wall Biosynthesis in Developing

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Cotton fibers are unicellular seed trichomes and consist of almost pure cellulose. During the transition from elongation growth to secondary wall thickening, the rate of cellulose biosynthesis in fibers rises nearly 100-fold. Although the first two cellulose synthase catalytic subunits (CesAs) were isolated from developing cotton fibers, it is not clear how many CesAs are involved in either primary or secondary wall synthesis in fibers, or how these genes are regulated during cell wall biogenesis. Cotton (Gossypium hirsutum) gene sequences from public databases that contained CesA motifs were classified into fourteen distinct CesA genes. The expression pattern of these genes was measured in field grown fibers for two growing seasons using quantitative RT-PCR. The first group of six GhCesA genes is preferentially expressed in elongating fibers, hypocotyls, and roots. The second group of six CesA genes is expressed specifically during the secondary wall thickening stage of fiber development. A third group comprised of two CesAs is expressed throughout fiber development. The results show that most GhCesA genes are developmentally regulated during fiber development, and that distinct multiple CesA genes are involved in either primary or secondary wall cellulose biosynthesis in cotton fibers. Recent progress on understanding the molecular basis for regulation of secondary wall CesA genes will also be discussed.