Study On The Physiological Mechanism And Transcription Analysis Of Tall Fescue Tolerance To Low Light Stress

Turf plays an important part on urban landscape.And it has a positive role in improving living environment.With the acceleration of urbanization,tall trees,shrubs,and buildings in landscaping often make turf grass in low light stress environment,leading to serious degradation of turf quality.Therefore,it’s important to investigate the shade tolerance of turfgrass.However,the research on tall fescue in response to low light stress is mostly about basic morphological,physiological,and biochemical parameters.There are few research reports on the mechanism(s)and transcriptome regulation(s)about the shade tolerance of tall fescue.In this study,twenty tall fescue cultivars widely used in landscaping were selected as research materials to screen and evaluate the shade-tolerant and shade-sensitive cultivars of tall fescue.The morphology,physiology,biochemistry,and transcriptome of two different shade-tolerant tall fescue cultivars under low light stress were measured to explored the response of the physiological mechanism and the different gene expression to shade tolerance.The results are as follows:(1)Twenty tall fescue cultivars that are widely used in landscaping were screened for turf characteristics.It indicates that low light stress significantly decreased the turf coverage,density,color,and NTEP score of each cultivar.And the shade tolerance of every cultivars under low light was different.Finally,we screened the shade-tolerant Arid Ⅲ cultivar and the shade-sensitive Airlie cultivar.Under low light,Arid Ⅲ had the best turf characteristics,and its turf coverage and density were better than those of the other cultiavars.Airlie had the lowest score of turf characteristics under low light stress.And its shade tolerance was the worst.(2)Low light stress significantly reduced the plant height,aboveground and underground biomass and inhibited the accumulation of photosynthetic pigments such as chlorophyll and carotenoids of Arid Ⅲ and Airlie.Low light stress significantly increased the malondialdehyde(MDA)content of the two tall fescue cultivars,and increased the activities of catalase(CAT),superoxide dismutase(SOD),and peroxidase(POD)of Airlie under low light stress.The SOD activity in Arid Ⅲ was significantly higher than that in Airlie(P<0.05).On the other hand,Pn,Gs and Ci of two different tall fescue cultivars were decreased significantly by low light stress(P<0.05).Low light stress likely inhibits the photosynthesis of tall fescue through stoma.Besides,Fv/Fm,ΦPSⅡ,qP and ETR of Airlie were decreased significantly under low light stress,while only qP and ETR were decreased significantly in Arid Ⅲ.The photosynthetic characteristics and chlorophyll fluorescence characteristics of Arid Ⅲ were better than those of Airlie under low light stress.(3)The transcriptome sequencing assembly of two cultivars obtained a matching rate of about 74.38% between 136,925 unigenes,and a total of 28,925 unigenes were annotated and classified in the KOG database.The transcriptional responses of Arid Ⅲ and Airlie to low light stress were different: 12,503 differentially expressed genes(DEGs)were up-regulated and12,441 down-regulated in Arid Ⅲ,and 14,696 DEGs were up-regulated and 16,120 down-regulated in Airlie.In addition,according,there were some common and different enrichment pathway of the DEGs in Arid Ⅲ and Airlie by the KEGG pathway analysis,regulating the response and shade tolerance to low light stress.The common part of transcriptional regulatory is composed of Alpha-linolenic acid metabolism,Phenylpropanoid biosynthesis,Glutathione metabolism,and Plant-pathogen interaction pathway.The different parts in two cultivars DEGs of photosynthesis pathway mainly down-regulated in photosystem Ⅱ,Photosynthethic electron transcription,and F-type ATPase,including PsbP,PsbQ,PsbR,PsbW,Psb27,Psb28,etc.Among them,the gene expression of Arid Ⅲ was less affected by low light stress.And the number of down-regulated genes and the degree of down-regulation of differential genes were significantly lower than those of Airlie,which showed that the gene changes in the photosynthetic pathway of Arid Ⅲ were more stable.Arid Ⅲ is less affected by low light stress.