| Coix is a gramineous crop with both medicine and food,and its yield is greatly affected by climate.The impact of drought on crop productivity and quality ranks first among all natural disasters.It poses a great threat to global food production and global economy.Many problems related to the response of plants to drought stress and its mechanism are still largely unknown.Therefore,improving the drought resistance of crops is one of the most important objectives of crop breeding.In this study,140 Coix germplasm resources were used as experimental materials to identify the drought resistance of Coix germplasm resources by setting two treatments of drought and control,and then using the identified high drought resistant material Xingren Xiaobai shell as materials to set four treatments of control,mild drought,moderate drought and severe drought.Through the study of the morphological,physiological and transcriptome characteristics of Coix seedlings under drought stress,Analyzing the physiological response and differential gene expression of Coix under drought stress can clarify the molecular response mechanism of Coix and provide a theoretical basis for cultivating new drought resistant Coix varieties.The main results are as follows:(1)The drought resistance index characters of Coix were defined.The drought survival rate of seedlings was positively correlated with leaf width,shoot fresh weight,shoot dry weight,root length and root fresh weight,positively correlated with leaf length,negatively correlated with plant height,and positively correlated with root dry weight.The drought resistance of Coix Germplasm Based on D value,CDC value and WDC value was similar.According to the cluster analysis of D value,the tested Coix germplasm can be divided into five drought resistance levels,including 3 in grade I,17 in grade II,9 in grade III,20 in grade IV and 1 in grade v.Except for leaf length,shoot fresh weight,shoot dry weight and root dry weight,the membership function value,CDC value,D value and WDC value of other indexes increased with the increase of drought resistance level.Stepwise regression analysis showed that the indexes closely related to D value were seedling drought survival rate,plant height,leaf width,root length and root fresh weight.(2)Drought stress had a significant effect on all indexes of Coix germplasm resources.Seedling survival rate,plant height,leaf width,root length and root fresh weight can be used as index characters to evaluate the drought resistance of Coix germplasm resources at seedling stage.Seven Coix Germplasm with strong drought resistance at seedling stage were selected,and Y1,ZF,Y3,Y12,Xingren small white shell,QL and ZY were selected,which can be used as research materials for drought resistance breeding,drought resistance mechanism and drought regulation and mitigation mechanism of Coix.(3)Drought stress significantly affected the growth of Coix seedlings.With the aggravation of drought,the growth of seedlings was seriously inhibited,the morphological indexes decreased significantly,and the fresh and dry weight of plants were affected by drought.The leaves of Coix lacryi are drooping and slightly curly under mild drought;In moderate drought,Coix leaves curl and some seedlings fall down;In severe drought,the Coix plant fell down,and the leaf tip and leaf edge withered.(4)Drought stress had significant effects on the physiology and biochemistry of Coix.The content of soluble protein and soluble sugar in leaves of Coix seedlings increased gradually with the degree of drought.The activities of antioxidant enzymes pod and cat in Coix seedlings also increased with the aggravation of drought.Under normal conditions,the internal structure of Coix seedling leaves is arranged regularly,and the cells are complete and clearly visible;Under mild drought treatment,the leaf cells of Coix were significantly reduced,the plasma wall was separated,the contents of chloroplast were not clear,and the lamellar structure was disordered;Under severe drought conditions,the cells of Coix leaves were broken,the cytoplasm leaked out,the chloroplasts separated from the cell wall,the chloroplast membrane was broken,the contents leaked out,and the integrity was damaged.(5)The molecular mechanism of Coix in response to drought stress was analyzed.Transcriptomics was used to analyze the changes of different genes in Coix after drought treatment at different times.The number of differentially expressed genes at3 h,6h,12 h and 24 h of drought treatment were 1904,1854,4417 and 5455 respectively.Go enrichment analysis of differentially expressed genes showed that differentially expressed genes were mainly enriched in catalytic activity and binding,metabolic process,cellular process,single biological process,membrane and membrane part.Coix can adapt to arid environment by regulating its growth,physiology and gene regulation.After the Coix lacryi felt the external signal under drought stress,it transmitted the signal of water shortage to the cell and induced the expression of regulatory genes,so as to affect the relevant elements of photosynthesis,reduce its photosynthesis,further affect the rate of carbon assimilation and the process of metabolic assimilation,and finally slow down the growth of Coix lacryi;With the prolongation of drought time,cell water loss induced the expression of osmotic regulation genes,increased the osmotic material balance in cells,and maintained the normal synthesis and metabolism of cells;In the process of drought stress,a large number of superoxide ions accumulate in the cells,activate the activity of antioxidant enzymes in Coix and remove superoxide ions through peroxide signal transmission,so as to effectively slow down the damage of cells caused by water shortage. |
