Physiological Response Mechanism And Expression Of Shade-related Genes In Eremochloa Ophiuroides Under Shading Stress

Lawns are an indispensable part of urban landscape design,which can improve and beautify the living environment and provide comfortable leisure places for people.With the continuous development of cities,tall buildings and trees often put lawns in a shaded environment,which seriously reduces the quality of lawns.Eremochloa ophiuroides（Munro.）Hack.is a perennial C₄warm-season turfgrass of the family Poaceae and subfamily Panicoideae,originating in China.It is known as“Chinese turfgrass”and is widely used in tropical and subtropical regions worldwide.The selection of shade-tolerant centipedegrass and clarification of its molecular mechanism have important practical significance and promotion value.There are some reports on the screening of shade-tolerant germplasm of centipedegrass,but the germplasm with extreme shade tolerance is relatively scarce,and the study of the molecular mechanism of shade tolerance in centipedegrass is relatively rare.In this study,16 different habitats of centipedegrass germplasm were used as test materials to screen for germplasm with better shade tolerance（CP11）and germplasm with poorer shade tolerance（CP2）.The physiological and biochemical indicators of the two germplasms under different shading treatments were analyzed,and the physiological mechanism of shade tolerance in centipedegrass and differentially expressed response genes were explored by combining transcriptome sequencing.The main conclusions are as follows:（1）Through the evaluation of centipedegrass germplasm from 16 different habitats under 99%shading treatment,it was found that shading stress significantly reduced the relative water content and chlorophyll content of each centipedegrass germplasm,while the relative conductivity and dead leaf rate increased significantly.There were significant differences in RWC,chlorophyll content,conductivity and dead leaf rate among different germplasms（P<0.05）.Under 99%shading for 12 days,CP11 showed strong shade tolerance with a chlorophyll content of 15.35 mg·g^-1and a relative water content of 95%,both maintained at a high level;CP2 had relatively poor shade tolerance,with a chlorophyll content of 5.16 mg·g^-1and a relative water content of 65%,both lower than other germplasms.（2）Using CP11 with strong shade tolerance and CP2 with weak shade tolerance as materials,three shading treatments of 33%,66%,and 99%were carried out.The results showed that with the deepening of shading stress and the extension of stress time,the root vitality of CP11 and CP2 and the SOD activity of roots and leaves showed a downward trend.Among them,after shading treatment of 66%for 18 days,the root SOD activity of CP11 decreased significantly by 47.13%compared with the control group,and the leaf SOD activity decreased significantly by 44.61%compared with the control group.The root SOD activity of CP2 decreased significantly by 64.11%compared with the control group,and the leaf SOD activity decreased significantly by 82.45%compared with the control group.After 12 days of shading treatment of 66%,there was no significant difference in root vitality of CP11 compared with the control group,while CP2 decreased significantly by 40.39%compared with the control group.Shading treatment significantly increased the content of malondialdehyde（MDA）in two centipedegrass germplasms,and the increase in CP11 at each stage and treatment was significantly lower than that of CP2.After 12 days of 99%shading treatment,the root MDA increase of CP2 was 3.4 times that of CP11,and the leaf MDA increase was 3.2 times that of CP11,indicating that the degree of membrane lipid peroxidation in CP2 was more serious than that in CP11.After6 days of 99%shading treatment,the proline increase in CP11 roots was 7.5 times that of CP2,and the soluble protein decrease in CP2 roots and leaves was 2.3 times and 3.5 times that of CP11,respectively.The soluble sugar content in CP11 roots increased by 55.69%compared with the control group,while that in CP2 roots decreased by 13.93%compared with the control group.（3）The two germplasms of CP11 with strong shade tolerance and CP2 with weak shade tolerance were subjected to 99%shading treatment for 12 days,and a total of460,309 Unigenes with an average length of 2007.6 bp were obtained through root and leaf transcriptome sequencing.Under shading treatment,there were 48,004 Unigenes with differential expression in CP11 leaves,of which 23,979 were up-regulated（49.96%）and24,025 were down-regulated（50.04%）.The CP2 germplasm with poor shade tolerance has53,486 DEGs,of which 24,355 are up-regulated（45.53%）and 29,131 are down-regulated（54.47%）.At the same time,the root system of CP11 has 145,958 Unigenes expression differences,with 78,584 DEGs up-regulated（53.84%）and 67,374 down-regulated（46.16%）.The CP2 germplasm with poor shade tolerance has 63,355 DEGs,of which36,780 are up-regulated（58.05%）and 26,575 are down-regulated（41.95%）.KEGG pathway enrichment analysis shows that the differentially expressed genes in the root system of CP11,which has strong shade tolerance,in the biosynthesis pathways of tetrahydrofolate,glycosphingolipid,and biological membrane synthesis,and the differentially expressed genes in the biosynthesis pathways of carotenoids,flavonoids,and isohydroxamic acid in leaves may be the main reasons for its strong shade tolerance.In addition,the gene changes in the photosynthetic pathway of CP11 are relatively stable and less affected by shading stress.QRT-PCR results show that candidate shade-tolerant genes Cp ANR,Cp CCo AOMT,Cp ASC and Cp ACOH may play a role in CP11’s resistance to shade stress.