||Gene expression profiling in soybean under aluminum stress: Transcriptome response to Al stress in roots of Al-tolerant genotype (PI 416937). Aluminum (Al) toxicity is a major constraint of crop production on acid soils. Many commercial soybean cultivars and advanced breeding lines have been evaluated for Al tolerance. Aluminum tolerance is quantitatively inherited trait in soybean making it difficult for genetic improvement. Understanding the molecular and genetic mechanisms of tolerance is crucial for developing efficient and effective programs aimed at improving Al tolerance trait The molecular mechanisms of Al tolerance is poorly understood in soybean. The objective of the research was to identify candidate aluminum tolerance genes in soybean Al-tolerant soybean genotype PI 416937 seedlings were exposed to zero or 10 M Al in growth chamber under hydroponic conditions for four time span of 2, 12, 48 and 72 hrs in a randomized complete block design with three replications. Microarray analysis was made on mRNA isolated from 1 cm log tap root tips using Affymetrix soybean array with over 68,000 probe sets Glycine max L and wild soybean combined. Both novel and known genes were discovered in response to Al treatment. They include Al tolerance relevant proteins, families of transcription factors, zinc finger, bZIP, WRKY, MYB, ADR6, and NAC domain proteins were induced likely regulating Al tolerance downstream genes. Stress related proteins, cytochrome P450, glutathione-s transferase, glutaredoxin family and ascorbic acid biosynthesis protein were induced as signatures of cellular detoxification mechanisms. An ABC type multidrug resistance protein that could act as citrate transporter or Al exporter was up-regulated, a key Al tolerance mechanisms in several species. A cell wall loosening enzyme endoxylglucan hydrolases were also up-regulated probably reversing the wall rigidification caused by Al and promoting root growth under Al stress. Phytosulfokines growth factor involved in cell division and proliferation was up-regulated likely as a direct counter action to Al toxicity which inhibits root growth by limiting cell division and elongation. In conclusion, the Al tolerance candidate genes identified herein are potential targets for future genetic engineering and molecular breeding work on Al tolerance trait in soybean which in turn would contribute to gain in soybean productivity on acid soils.