A Study On The Mechanism Of Exogenously Supplied ABA-mimicking Ligand AM1 On Improving Cold Tolerance Of Bermudagrass

Bermudagrass (Cynodon dactylon) belonging to Poaceae family is a kind of warm-season perennial grass.Low temperature is generally considered to be the key factor limiting the growth of bermudagrass. Recent studies indicated that exogenous application of small molecules regulated plants response to abiotic stress at the physiological and molecular levels, resulting in increased cold stress tolerance.In this study, small molecules AM1, which is an ABA-mimicking ligand, was used to test protective effect on cold tolerance of bermudagrass. Phenotypic and physiological changes showed that AM1 was effective to increase bermudagrass cold resistance. The main conclusions were as following:In contrast to the control, exogenous AM1 treatment significantly improved the cold tolerance of bermudagrass seedlings, including promoted growth,decreased conductivity, and increased survival rate in bermudagrass seedlings.AM1 treatment reduced contents of H2O2, O2-1, OH·and MDA, and increased activities of antioxidant enzymes SOD, POD, GR and GPX. Morever, proline was accumulated in bermudagrass after AM1 treatment, indicating that these substances were also involved in osmotic adjustment in bermudagrass after AM1 treatment.Based on transcriptome data of bermudagrass, we cloned DREB1 genes, including size 1563, size1539, size1201. These genes shared high similarity and were splicing variant of DREB1. The real-time PCR results showed that size 1539 gene was up-regulated 4.22 times after 3 h cold treatment indicating this gene is cold inducible. Moreover, AM1 treatment suppressed expression level of DREB1 when compared to control.Both low temperature and exogenous AM1 can regulate the expression of DREB, AP2/ERF, OSMOTIN, IscS, SOD, POD, CAT in Bermudagrass under cold stress.While during the treatment,the expression of LEA has keeping a low level, neither AM1 can upregulated its expression.Cold stress response involved in multi-complex signaling transduction pathways, including ABA depedent and ABA independent pathways. AM1 treatment on bermudagrass in this study showed decreased conductivity, and increased survival rate and fresh weight. Physiological data indicated that exogenous AM1 treatment significantly reduced superoxide anion radical content and increased antioxidant enzyme activity to keep the homostasis of reactive oxygen metabolism, as well as accumulation of osmotic substance. At the molecular level, both low temperature and exogenous AM1 can regulate the expression of DREB, AP2/ERF, OSMOTIN, Lea, IscS, SOD, POD, CAT in Bermudagrass under cold stress.This study showed that AM1 is effective in increasing bermudagrass cold stress tolerance and provided theoretic fundament for improvement of paint cold tolerance, which will be helpful for the extension of plant green period and increasing plant abiotic stress tolerance.