LAUSR

Drought is a yield-limiting factor for soybean (Glycine max L. Merrill) production in North America. Understanding molecular mechanisms underlying early responses of the soybean plant to drought may help develop new techniques to manage the abiotic stress. The objectives of this research were to identify expressed genes responsive to drought stress at the seedling stage and to develop biomarkers for early diagnostic of genotypic difference in the stress tolerance. Using a GeneChip Soybean Genome Array and an improved algorithm, we identified 697 differentially expressed genes (DEGs), with 420 upregulated and 277 downregulated by a 6-h dehydration treatment. A majority of these DEGs encode transcription factors, protein kinases, hormone biosynthetic/signaling enzymes, or other regulatory proteins. MAPMAN and KEGG enrichment showed that the DEGs were mainly involved in the metabolic and hormone signaling pathways and identified the GmHDZ72/PYL/PP2C module as negative feedback of abscisic acid signaling pathway induced by dehydration stress. Ten DEGs were selected from various pathways and validated in a sample of 20 soybean cultivars varying in the level of drought tolerance. Five of the 10 validated DEGs, Glyma03g30040, Glyma11g05960, Glyma11g11430, Glyma12g22880, and Glyma16g02390, showed expression profiles strongly correlated with the plant height reduction after a 14-d drought treatment. These genes are the best candidate biomarkers to monitor plant early responses to drought stress before a symptom appears and to screen for drought-tolerant genotypes. This research provided a new set of transcriptomic data to develop gene regulatory networks underlying sensing drought signal and possible acclimatization in the early stage and enriched the genomics toolbox with a set of biomarkers for early diagnosis of drought damage and molecular breeding of drought tolerance in soybean.