ABSTRACT: We have previously reported that the responses of tobacco tissues treated with AaGlucan are similar to those for laminarin [1]. To better understand the overall responses and signaling pathways in tobacco, we have identified here AaGlucan and laminarin early response genes, using a custom 16K BY-2 microarray [2,3]. BY-2 cells were treated with laminarin or an AaGlucan-enriched fraction prepared from A. alternata 102 culture-medium and subjected to microarray analysis. [1] Shinya, T., Menard, R., Kozone, I., Matsuoka, H., Shibuya, N., Kauffmann, S., Matsuoka, K. and Saito, M. (2006) Novel b-1,3-, 1,6-oligoglucan elicitor from Alternaria alternata 102 for defense responses in tobacco. FEBS J. 273: 2421-2431. [2] Matsuoka, K., Demura, T., Galis, I., Horiguchi, T., Sasaki, M., Tashiro, G. and Fukuda, H. (2004) A comprehensive gene expression analysis toward the understanding of growth and differentiation of tobacco BY-2 cells. Plant Cell Physiol. 45: 1280-1289. [3] Galis, I., Simek, P., Narisawa, T., Sasaki, M., Horiguchi, T., Fukuda, H. and Matsuoka, K. (2006) A novel R2R3 MYB transcription factor NtMYBJS1 is a methyl jasmonate-dependent regulator of phenylpropanoid-conjugate biosynthesis in tobacco. Plant J. 46: 573-592. AaGlucan was purified from Alternaria alternata 102 as a potent elicitor for tobacco [1] Four-day-old tobacco BY-2 cells after subculture were treated with 10 microg/ml AaGlucan enriched fraction for 1h. Total RNA was prepared from the control and treated samples and used for microarray experiment after reverse transcription and labeling with Cy5 fluorescent dye. [1] Shinya, T., Menard, R., Kozone, I., Matsuoka, H., Shibuya, N., Kauffmann, S., Matsuoka, K. and Saito, M. (2006) Novel b-1,3-, 1,6-oligoglucan elicitor from Alternaria alternata 102 for defense responses in tobacco. FEBS J. 273: 2421-2431.