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Major Gene Expression Changes Occur While Gravity Is Directing the Polarity of Fern Spore Development. M.L. Salmi, S.C. Stout and S. J. Roux. Sect. Molecular Cell & Developmental Biology, Univ. Texas, Austin, TX.

   As an approach to understanding the genetic basis of gravity responses we are using germinating spores of the fern Ceratopteris richardii. Gravity determines the developmental polarity of the single-celled spore within the first 24 hours after it is induced by light to begin its germination. Using cDNA microarrays containing 3,207 unique Ceratopteris richardii genes we have evaluated the pattern of expression over the first 48 hours of spore growth, which includes the period during which gravity determines the polarity of spore development. These genes were analyzed by BLAST comparison with the Arabidopsis thaliana proteome and 2,595 (80.9%) of them had an Arabidopsis analog of significant E-value (less then 0.1). Four comparisons of different time points after germination initiation were made with a minimum of 8 microarray replications for each comparison. After applying stringent criteria for spot quality and amount of replication, relative expression levels for 3,143 Ceratopteris genes were determined using a Bayesian method of statistical analysis (BAGEL software). In this analysis, significant expression changes between time points are defined by non overlapping 95% credible intervals and are independent of the magnitude of the expression change. Ceratopteris sequences were also annotated based on BLAST similarity with the NCBI non-redundant database and these gene identities were used for the 919 Ceratopteris genes (29%) that showed a significant change between any of the five time points analyzed. The remaining 71% of the genes showed no statistically significant change in transcript abundance during the first 48 hours of development. We have recently obtained some 1,536 more EST sequences and produced another microarray containing 5,376 spots. This new array will be used to evaluate gene expression changes in spores developing in microgravity (from STS-93) compared with spores developing in 1g. (Supported by NASA grants NAG2-1586, NAG10-295 to S.J.R. and NGT5-50371 to S.C.S.)