A FIBERLESS SEED MUTATION IN COTTON IS ASSOCIATED WITH LACK OF FIBER CELL INITIATION IN OVULE EPIDERMIS AND ALTERATIONS IN SUCROSE SYNTHASEEXPRESSION AND CARBON PARTITIONING IN DEVELOPING SEEDS

Fiber cell initiation in the epidermal cells of cotton (Gossypium hirs utum L.) ovules represents a unique example of trichome development in higher plants. Little is known about the molecular and metabolic mech anisms controlling this process. Here we report a comparative analysis of a fiberless seed (fls) mutant (lacking fibers) and a normal (FLS) mutant to better understand the initial cytological events in fiber de velopment and to analyze the metabolic changes that are associated wit h the loss of a major sink for sucrose during cellulose biosynthesis i n the mutant seeds. On the day of anthesis (0 DAA), the mutant ovular epidermal cells lacked the typical bud-like projections that are seen in FLS ovules and are required for commitment to the fiber development pathway. Cell-specific gene expression analyses at 0 DAA showed that sucrose synthase (SuSy) RNA and protein were undetectable in ils ovule s but were in abundant, steady-state levels in initiating fiber cells of the FLS ovules. Tissue-level analyses of developing seeds 15 to 35 DAA revealed an altered temporal pattern of SuSy expression in the mut ant relative to the normal genotype. Whether the altered programming o f SuSy expression is the cause or the result of the mutation is unknow n. The developing seeds of the fls mutant have also shown several corr elated changes that represent altered carbon partitioning in seed coat s and cotyledons as compared with the FLS genotype.