Mechanism Of PhyA In Response To Drought Stress In Peanut

Peanut is an important oil crop in China,mainly distributed in arid and semi-arid areas.The severe shortage of water resources has become an important factor restricting peanut production.Drought affects not only the growth and development process of peanut from germination to maturing,but also seriously affect the quality and yield of peanut.Therefore,it is of significance to study the drought resistance mechanism for developing drought-resistant peanut varieties and improving peanut yield and quality.Light,an important environmental factor,affects the growth and development of plants.Plants not only rely on photosynthesis to obtain energy,but also perceive light quality and direction through photoreceptors to regulate their growth and development.Phytochrome A(phyA)and phyB are mainly red and far-red light receptors,which involve in the important process of plant growth and development.Furthermore,phyB also play a key role in biotic and abiotic stresses in plants.However,the roles and mechanisms of phyA involved in plant response to stress are not known.Stable peanut phyA overexpression lines(OEAhphyA)were obtained in the previous study.In this study,20% PEG treatment and natural drought stress(restrict watering)were conducted during seed germination and seedling stage of OEAhphyA and LH14 to investigate the mechanism of peanut phyA overexpression in response to drought stress.The main results are as follows:1.During the seed germination period,after 20% PEG treatment the germination rates of three OEAhphyA lines(as 6B4,6B9 and 6A12)were 18%,38% and 15%,respectively,which were significantly lower than the control LH14(93%).The germination index of the OEAhphyA lines(6B4,6B9 and 6A12)were remarkablely reduced to compare with LH14,and the time to reach the germination peak was also significantly delayed.The results indicated that the overexpression of AhphyA increased sensitivity to PEG treatment during peanut seed germination.2.LH14 and OEAhphyA seedlings of 10 d were treated with 20% PEG.The OEAhphyA lines treated with 20% PEG for 2 d showed a lighter wilting degree to compare with the control LH14.The detached leaves of LH14 and OEAhphyA lines were placed in the laboratory for drying under constant temperature,protected from wind direct sunlight.The water loss rates of the OEAhphyA lines(6B4,6B9 and 6A12) were significantly lower than that of LH14.OEAhphyA lines had higher water retention capacity,and higher tolerance to drought stress to compare with LH14.After 20% PEG treatment,the MDA contents of the OEAhphyA lines were significantly lower than that of LH14,and the CAT activity was significantly higher than that of LH14.The contents of proline,soluble sugar,and soluble protein of the OEAhphyA lines were significantly increased.The soluble protein content was significantly higher than that of the control LH14.The leaf chlorophyll fluorescence parameters Fv’/Fm’,ФPSⅡ,qP,ETR and Fv/Fm of the OEAhphyA lines were all higher than those of LH14.These results indicated that the overexpression of AhphyA increased the tolerance of peanut seedlings to PEG treatment.3.The 25 DAP (days of planting) LH14 and OEAhphyA seedlings,grown under the normally watered soil potting conditions,were subjected to natural drought stress.After stopping watering for 16 d,it was found that the leaves of the OEAhphyA lines were naturally stretched and the stems and leaves were less wilted to compare with LH14.The change of MDA content,osmotic adjustment substances(proline,soluble sugar and soluble protein content),Fv/Fm and other leaf chlorophyll fluorescence parameters after drought stress and PEG treatment were consistent.However,SOD,POD and CAT antioxidant enzyme activities,changes after drought stress and PEG treatment were inconsistent.These results further indicated that the overexpression of AhphyA improved the drought tolerance of peanut seedlings.4.In order to study the mechanism of phyA improving the drought tolerance of peanut seedlings,20% PEG treated seedlings of LH14 and OEAhphyA lines used for gene expression analysis.The expression of genes involved in osmotic regulation,antioxidant enzymes and stress-related genes and transcription factors changed significantly after 20% PEG treatment.The differentially expressed genes under PEG treatment were mainly related to stimulus response,biological regulation and other biological processes and molecular functions,some signal transduction,carbohydrate metabolism and other metabolic pathways.After 20% PEG treatment for 4h,the expression levels of endoglucanase 8-like gene,proline-rich protein 2-like gene,cyanogenic beta-glucosidase-like gene,beta-glucosidase 12-like gene were significantly up-regulated.In OEAhphyA lines,the expression levels of beta-amylase-like gene and sucrose synthase-like gene were significantly down-regulated after 20% PEG treatment for 4 h.These results indicated that AhphyA improved the resistance of peanut to drought stress by regulating the expression of osmotic regulation-related genes and increasing the accumulation of osmotic substances,thus reducing the water loss rate of peanut leaves,reducing the damage degree of leaf membrane lipid,and improving the photochemical reaction efficiency of peanut seedlings.