Lipid- and calcium-signaling regulation of HsfA2c-mediated heat tolerance in tall fescue

Heat stress transcription factor A2c (HsfA2c) is known for its positive roles in conferring heat tolerance. The objectives of this study were to examine the effectiveness of selected signaling molecules for improving heat tolerance of a cool-season grass species, tall fescue (Festuca arundinacea Schreb.) and to determine the signal transduction pathways regulated by those molecules through the activation of HsfA2c and heat shock proteins (HSP). Foliar application of phosphatidic acid (PA), calcium chloride (CaCl2), hydrogen peroxide (H2O2), salicylic acid (SA) and trans-zeatin riboside (t-ZR) all activated expression of HsfA2c and several HSP genes, and enhanced tall fescue tolerance to prolonged periods of heat stress (38/33 degrees C, day/night temperature). Exogenous application of all the molecules increased photosynthetic activities and membrane stability of tall fescue exposed to heat stress, with PA (25 mu M) and CaCl2 (10 mu M) having more pronounced effects than other treatments. PA- and Ca2+ mediated heat tolerance was associated with the regulation of HsfA2c and small HSPs (Hsp18) during short-term heat stress and with large HSPs (Hsp70 and Hsp90) during prolonged heat stress, involving genes in PA synthesis and catabolism, and the downstream genes of the Ca2+ signaling pathways. These results suggest the transcriptional regulation of HsfA2c-mediated heat tolerance involving lipid and calcium signaling pathways in tall fescue. (C) 2017 Elsevier B.V. All rights reserved.