The response of plants to water deficits depends on the extent and rate of water loss and its timing and duration. As a physical stress, water deficit elicits biochemical responses through a signaling cascade that includes stress perception, signal transduction and regulation of gene expression. To understand the regulatory networks and mechanisms of drought tolerance, more comprehensive approaches including quantitative and qualitative analyses of gene expression products are necessary at the transcriptome, proteome, and metabolome levels. In addition to the molecular genetic approaches, current work in our laboratory covers the following areas.

Physiology and genetic variation of root growth under water deficit:
An important feature of root system responses to soil drying is the ability of the roots to continue elongation at low water potentials that completely inhibit the shoot growth. In collaboration with Dr. Robert Sharp at the University of Missouri (MU) we are studying the spatial and temporal pattern of cell expansion within the root growth zone to understand the physiological mechanisms, which further support the functional genomic analysis. An interest in our lab is comparative legume root biology and associated drought responses. We are also investigating genetic variation in root architecture and plasticity under drought in collaboration with Drs. Robert Sharp, David Sleper, and J. Grover Shannon, all at MU. This work includes field screening of soybean plant introductions in collaboration with Dr. Jim Specht, at the University of Nebraska-Lincoln. Characterization of soybean germplasm for physiological responses to drought focusing on root biology facilitates dissecting Quantitative Trait Loci (QTL) related to root and drought traits, and its further applications in molecular breeding and biotechnology.

Transcript profiling:
We are conducting gene expression profiling studies of soybean tissues including roots, leaves, and seed filling stages under drought stress to elucidate the pattern of gene expression and signaling cascades. We are utilizing deep sequencing technology platforms such as 454 and Solexa to capture maximum and rare transcript expression patterns under water deficit conditions. We have constructed normalized cDNA libraries from the drought stressed root tissue at the V3 stage and sequenced Expressed Sequence Tags (ESTs) and full-length complementary DNA (FLcDNA) in collaboration with the Department of Energy-Joint Genome Institute (DOE-JGI) help to identify more stress related and root specific transcripts. Affymetrix gene chip and custom built microarray analyses are employed to discover the differential expression pattern of drought specific genes. In collaboration with Drs. Gary Stacey and Dong Xu, at MU, we have identified soybean transcription factors (TFs) through genome mining. A library of RT-PCR primer sets of soybean TFs were synthesized. We are utilizing this TF resource to discover tissue specific and stress specific regulatory switches of various stages of soybean development. We are also conducting comparative genomics analysis between soybean, Medicago truncatula, Arabidopsis, and maize. All these studies help predict and construct the soybean root transcriptome map. To achieve gene function at the right time of stress and in the right tissue, we are in pursuit of stress specific and tissue specific (focusing on root) promoters. To discover gene regulation mechanisms, we are studying root and water stress specific small RNAs discovered through various methods including Solexa sequencing of microRNA libraries (in collaboration with Martin Crespi, France). We are utilizing the model plant Arabidopsis for the functional characterization of various regulatory factors and this approach will help further select candidate genes for soybean engineering.