The Influence Of Day And Night Changes Of Sugar Metabolism On Tomato Botrytis Cinerea Resistance And Mechanism Involved

The aim is to clarify the influence of sugar metabolism on the resistance of tomato gray mold and its possible mechanism,and provide a theoretical basis for the breeding of new tomato varieties with resistance to gray mold.In this experiment,the leaves sampled in the morning（sampling at 8 o’clock in the morning）and evening leaves（sampling at 6 o’clock in the evening）with different carbohydrate metabolism characteristics were separately inoculated with a gray mold spore suspension.The size of the lesion was observed and the difference after inoculation was observed.Period（0,36h and 60h）the content of starch and soluble sugar in tomato leaves,invertase activity,salicylic acid（SA）and jasmonic acid（JA）content,cell death and hydrogen peroxide accumulation,tomato and pathogenic invertase and Determination and analysis of sugar transporter and tomato disease resistance-related gene expression.The main results are as follows:（1）The leaves sampled at night are more resistant at the early stage of inoculation（36h）than the leaves sampled in the morning,showing smaller lesions and lower growth of Botrytis cinerea.However,at the late stage of inoculation,there was no significant difference in the size of the diseased spots and the growth of Botrytis cinerea in the early and late samples.（2）The reduction of cell death enhances tomato resistance to Botrytis cinerea.After inoculation,compared with the leaves sampled in the morning,the cell wall invertase（CWIN）activity and the expression level of catalase gene Sl CAT2 in the leaves sampled at night were higher,resulting in no H₂O₂ signal;the expression levels of（programmed cell death,PCD）-related genes（Sl SPL,Sl SBT3 and Sl CYP1）were higher.low.The cell death of the leaves sampled at night is reduced,thereby enhancing the resistance of the leaves sampled at night to the dead vegetative pathogen Botrytis cinerea.（3）On the one hand,the decomposition of sucrose can provide energy for the defense response of plants.On the other hand,the hexose produced by the decomposition of sucrose can be used as a sugar signal to regulate the expression of disease-related genes and enhance the resistance of plants to pathogens.Our measurement results show that during the entire inoculation period（0-60h）,compared with the leaves sampled in the morning,the leaves sampled at night have relatively higher starch and hexose（glucose and fructose）content;on the contrary,0h after inoculation sucrose content in the leaves sampled in the morning was significantly higher than that in the leaves sampled in the evening,which indicated that Botrytis cinerea might be a low-sugar pathogen.In addition,the up-regulation of the expression level of LIN8 in the leaves sampled at night leads to an increase in CWIN activity.The increase in CWIN activity can decompose more sucrose into hexose,and can also increase the content of disease resistance hormone JA,and enhance the resistance of the leaves sampled at night to Botrytis cinerea.（4）Increased activity of the anti-disease hormone JA and ET signal pathways enhance plant resistance.36h after inoculation,the JA content of the leaves sampled at night was significantly higher than that of the leaves sampled in the morning.In addition,the expression level of Sl Pti4,a gene related to ethylene signaling,was also significantly higher in the leaves sampled at night than in the leaves sampled in the morning.The expression levels of disease resistance-related genes（Sl PR1a2,Sl PR2,Sl PR5,Sl MYC2 and Sl WRKY72b）were also significantly higher than that of leaves sampled in the morning.At the same time,as a negative regulator of PR gene expression,the expression level of Sl NPR1 in the leaves sampled at night was significantly lower than that of leaves sampled in the morning.Thereby enhancing the resistance of the sampling leaves at night to Botrytis cinerea.（5）The effect of sugar transporter on plant disease resistance.Compared with the leaves sampled in the morning,the leaves sampled at night have a relatively higher expression level of SWEET and a relatively lower expression level of STP after inoculation,which may increase the concentration of extracellular sugar in the leaves sampled at night,which is conducive to the onset of pathogens.But 60h after inoculation,the expression levels of Bc HXT1,Bc HXT6 and Bc HXT13 in the leaves sampled in the morning were significantly higher than those sampled in the evening,resulting in the inefficient use of the sugar in the leaves sampled in the evening,resulting in decreased pathogenicity of Botrytis cinerea and disease resistance of tomatoes Sexual increase.