Differential gene expression in shoots and roots under heat stress for a geothermal and non-thermal Agrostis grass species contrasting in heat tolerance

Identification of genes associated with heat tolerance is important for developing heat-tolerant plants. The objectives of this study were to compare genes differentially expressed in shoots and roots in two Agrostis grass species contrasting in heat tolerance under different temperature regimes and to identify up-regulated genes associated with heat-stress adaptation in Agrostis grass species. Heat-tolerant, thermal A. scabra, adapted to geothermal areas in Yellowstone National Park, and heat-sensitive A. stolonifera, used as a turf and forage grass in cool climatic regions, were exposed to 20 or 40 °C in growth chambers. Leaves and roots were sampled at 7 day of treatment to evaluate physiological responses to heat stress and to perform differential display analysis. Thermal A. scabara maintained significantly higher leaf chlorophyll content and root viability and lower electrolyte leakage (EL) following 7 day of heat stress, compared to A. stolonifera. Differential display analysis of leaf samples revealed that 21 gene fragments were down-regulated while 18 fragments were up-regulated in heat-stressed A. stolonifera. For thermal A. scabra, 38 gene fragments were down-regulated and 22 fragments were up-regulated under heat stress. Four gene fragments in roots were found to be up-regulated under heat stress. RT-PCR analysis confirmed that one gene fragment in leaves (AsL9) and two gene fragments in roots (AsR1 and AsR2) were expressed only in thermal A. scabra exposed to heat stress. These heat-inducible genes in thermal A. scabra may contribute to its superior ability to survive in chronically high-temperature soils in geothermal areas. Putative functional analysis with BLASTX found that most of the up-regulated genes in both species were involved in stress defense pathways or tolerance mechanisms, such as cell wall elasticity, secondary metabolism, regulatory functions, and protein synthesis.