An ABA inducible WRKY gene integrates responses of creosote bush (Larrea tridentata) to elevated CO2 and abiotic stresses

The physiological and molecular responses of Larrea tridentata, an evergreen desert shrub, to elevated CO2, and abiotic stresses were examined to enhance our understanding of the crosstalk of hormones, stresses, and elevated CO2 in signaling. Under nonlimiting conditions of water and nutrients, elevated CO2 increased both ABA and starch concentrations in leaves by two-fold. Combinations of elevated CO2 and water deficit treatments further increased the concentrations of ABA, but not starch. A transcription factor, LtWRKY21, was cloned from Larrea tridentata to address questions regarding crosstalk at the molecular level. The expression of LtWRKY21 was enhanced by elevated CO2, water deficit, high salinity, and wounding. In addition, ABA, jasmonic acid (JA), and glucose induced the expression of LtWRKY21. However, cold and heat treatments decreased the wounding-induced LtWRKY21 mRNA level. Transient expression of LtWRKY21 suggests that this transcription factor acts as an activator of ABA signaling and as a repressor of gibberellin (GA) signaling. These results suggest that LtWRKY21 might function as a key regulator of signaling networks in Larrea tridentata.