Auxin Is Involved Inttranscriptional Regulation of Gossypium Hirsutum Cellulose Synthase Catalytic Subunit 4 in Transgenic Arabidopsis and Cultured Cotton Fibers

Cotton (Gossypium hirsutum L.) fibers are unicellular trichomes originating from the ovule epidermis and consist of almost pure cellulose.  Gossypium hirsutum cellulose synthase catalytic subunit 4 (GhCesA4) and other genes involved in cellulose biosynthesis in developing cotton fibers are transcriptionally co-regulated.   GhCesA4 is significantly up-regulated at the transition from primary to secondary wall biosynthesis during fiber development.  To study transcriptional regulation of cellulose biosynthesis in cotton fibers, the GhCesA4 promoter fused to b-glucuronidase reporter gene was transformed into Arabidopsis and cotton tissues.  Tissue preferential expression patterns of GhCesA4 in transgenic Arabidopsis were similar to those in cotton.  GhCesA4 was developmentally-regulated in leaf trichomes and vascular of transgenic Arabidopsis as in cotton fibers.  During Arabidopsis leaf vascular development, temporal expression patterns of GhCesA4 matched the pattern of gradual shifts of temporal auxin production in the leaf.  Auxin up-regulated GhCesA4 in lateral roots, but down-regulated GhCesA4 in primary roots of Arabidopsis.   Furthermore, the expression of GhCesA4 in Arabidopsis leaf trichomes was fully inhibited by an auxin transport inhibitor.   In cultured cotton fibers, GhCesA4 was also up-regulated by auxin.  Our results show that auxin may play roles in transcriptional regulation of GhCesA4 and other co-regulated genes that are involved in secondary cell wall cellulose biosynthesis during cotton fiber development.