Biochemical traits and pathways associated with heat tolerance in fine fescue

Heat stress is a major factor that causes the summer decline in turfgrass especially for the cool-season species. Understanding the heat tolerance mechanism would provide basis for effectively managing heat damage during summer time and breeding heat tolerant cultivars. In this thesis, the variance in heat tolerance among fine fescue species and cultivars were evaluated; key factors, in the physiological, biochemical and proteomic aspects, associated with the heat tolerance were identified and the heat tolerance mechanism in fine fescue was elucidated. The dissertation is mainly composed of four parts. In the first part, a total of 26 fine fescue cultivars were evaluated for their heat tolerance and drought tolerance by physiological parameters. The result indicated that heat stress is much more detrimental to fine fescue species compared to drought stress. Additionally, several cultivars with good heat tolerance or drought tolerance were selected, the heat tolerant cultivars include ‘Blue Ray’, ‘Spartan II’, ‘MN-HD1’, ‘Shoreline’, ‘Navigator II’, ‘Azure’, ‘Beacon’, ‘Aurora Gold’, ‘Reliant IV’, ‘Marco Polo’, ‘Garnet’, ‘Wendy Jean’, ‘Razor’, and ‘Cindy Lou’, while the drought tolerant cultivars include ‘Spartan II’, ‘MN-HD1’, ‘Reliant IV’, ‘Garnet’, ‘Azure’, and ‘Aurora Gold’. These cultivars could be used in hot and/or dry environments and as breeding germplasms for developing heat and/or drought-tolerance. To further elucidate the heat tolerance mechanism in fine fescue, in the second part, the differential membrane composition (fatty acids, sterols and membrane proteins) change under heat stress was compared between heat tolerant fine fescue cultivar ‘Reliant IV’ and heat sensitive fine fescue cultivar ‘Predator’. This experiment found that the better heat tolerance in ‘Reliant IV’ is associated with greater increase of ethyl sterols (sitosterol, stigmasterol, avenasterol and fucosterol), unsaturated long chain fatty acids (18:1 and 18:2), less severe down-regulation of membrane proteins involved in photosynthesis, protein modification and signaling and greater up-regulation of heat responsive proteins, including Rubisco activase and disease resistance protein 1. In the third part, the differential response of free amino acids and soluble proteins to heat stress were compared between ‘Reliant IV’ and ‘Predator’. This experiment found that the heat tolerant ‘Reliant IV’ exhibited greater accumulation of seven essential amino acids (histidine, glutamine, glutamate, proline, threonine, aspartate and tryptophan) and several soluble proteins, including glyceraldehyde 3-phosphate dehydrogenase, triosephosphate isomerase, dihydrolipoyl dehydrogenase, malate dehydrogenase, Rubisco large subunit binding protein subunit alpha, protein disulfide-isomerase, catalase, calcium-transporting ATPase, lectin-domain containing receptor kinase, stromal 70 kDa heat shock-related protein, 20 kDa chaperonin, actin, tubulin beta-2 chain, aspartate aminotransferase, formate dehydrogenase and UDP-sulfoquinovose synthase. These differentially accumulated free amino acids and soluble proteins could be associated with the genetic variation in heat tolerance of fine fescue. In the last part, the differential change of phenolic composition under heat stress was compared between ‘Reliant IV’ and ‘Predator’. A total of 12 phenolic acids were identified in the leaves of fine fescue cultivars. The result indicated that homovanillic acid and caffeic acid were more up-regulated in ‘Reliant IV’ under short-term heat stress, while 3, 4-dyhydroxybenzoic acid showed greater accumulation in ‘Reliant IV’ under long-term heat stress. These greater accumulated phenolic acids could account for the better heat tolerance in ‘Reliant IV’ and be potentially used as heat stress reliever in cool-season grass species. In summary, these studies identified a series of components (metabolites or proteins) that associated with heat tolerance in fine fescue. These identified components could potentially be incorporated into bio-stimulant product to relieving heat damage or serve as basis to develop molecular marker in assisting heat-tolerant germplasms selection.Ph.D.Includes bibliographical referencesby Jinyu Wan