The Mechanism Of DSF Regulating Plant Disease Resistance,promoting Primary Root Growth And The Preliminary Application Of Dsf In The Control Of Cabbage Black Rot

The Quorum sensing（QS）is a mode of communication between bacteria,which can regulate a variety of community behaviors among bacteria.It has been shown that QS signaling molecules can be perceived and responded to not only by bacteria but also by the host plant,thereby regulating plant growth and disease resistance,and mediating cross-kingdom communication between bacteria and plants.Diffusible Signaling Factor（DSF）is a newly discovered signaling molecule for the Gram-negative bacterial population to sense intercellular communication in recent years.It was first isolated and identified from Xanthomonas campestris pv.campestris（Xcc）.Nowadays,emerging evidence elucidate the mechanism of biosynthesis pathways and regulatory mechanisms of DSF.In addition,DSF is known to induce defense-related responses in plants.However,how plants perceive DSF is still unclear,and the effects of DSF on plant growth and development is still unclear too.Previous studies in our laboratory showed that DSF could induce disease resistance of Arabidopsis against black rot bacteria,but the mechanism is not clear.In this study,the model plants Arabidopsis and cabbage were used as experimental materials,and Xcc was used as the indicator bacteria to explore the signaling pathways affecting DSF-induced plant disease resistance,and to analyze the molecular mechanism of DSF-induced plant disease resistance response.The primary root length and lateral root density were used as indicators,to explore the effect and mechanism of DSF on plant root growth.Meanwhile,cabbage was pretreated with DSF to detect the control effect of cabbage black rot.The main study results are as follows:1.By observing the disease index of detach leaves and measuring the number of pathogenic bacteria colonized in plants,it was found that after DSF pretreatment and inoculation with pathogenic bacteria,the disease index of Arabidopsis wild-type was reduced,the number of colonized bacteria in plant cells was reduced,and there was an obvious and stable resistance.While the JA-deficient plants did not show resistance.Meanwhile,the JA content and related genes expression were significantly upregulated.This study indicated that DSF dependent JA signaling induces resistance to black rot in Arabidopsis.Similarly,experiment found that SA-deficient Arabidopsis did not show resistance,and the associated genes expression level were upregulated at 6 h.I speculate that SA may also be involved in DSF-induced disease resistance at an early stage of plant recognition of Xcc.2.By DAB staining,hydrogen peroxide content determination,it was found that DSF pretreatment accelerated the generation and accumulation of H₂O₂.Through the determination of peroxidase（POD）and phenylalanine ammonia lyase（PAL）activities,it was found that DSF treatment maintained higher POD and PAL enzyme activities.This leads to the transduction of plant defense signaling that leads to resistance.3.Through the measurement of primary root length,it was found that 2μmol/L DSF can significantly promote the growth of primary root of Arabidopsis,and induce the formation of lateral roots and root primordia.Using stereoscopic microscopy,it was found that DSF promoted cell division in the root apical meristem and cell expansion in the elongation zone of Arabidopsis.By measuring the expression levels of auxin-related genes,it was found that DSF significantly up-regulated the expression of the auxin synthesis gene YUC7,and DSF could not induce elongation of primary roots in the auxin synthesis-deficient mutant yuc7.Further studies revealed that DSF could induce upregulation of the expressions of ARF5 and ARF7,the key transcription factors of auxin regulation.Meanwhile,DSF induced expression and transcriptional upregulation of auxin transporter gene PIN3.It shows that DSF can induce the synthesis of auxin,affect the distribution and response of auxin,then regulate the growth of plant roots.4.The changes of ROS in Arabidopsis root tips were observed by fluorescence microscopy,and DSF was found to promote the production of ROS.While catalase（CAT）attenuated DSF-induced ROS accumulation.At the same time,the mutant robh D/F defective in ROS production is less sensitive to DSF.This result indicates that DSF regulates the growth of Arabidopsis roots by regulating ROS synthesis.5.The potted cabbage and the detached leaves,inoculated with the pathogen Xcc,it was found that DSF attenuated the symptoms of black rot in cabbage and induced resistance to Xcc.In conclusion,DSF may induce the resistance of Arabidopsis to black rot through the JA signaling pathway,and SA may be involved in this process in the early stage.The DSF also induces the ROS production and accumulation.DSF can promote the elongation of the primary root in Arabidopsis,and auxin and ROS are involved in the regulation of root growth by DSF.At the same time,it is preliminarily proved that DSF can be used to control black rot in cabbage.It provides theoretical support for the development and application of DSF as a novel plant elicitor.It also provides a certain reference for studying the signal transduction mechanism of cross-kingdom communication between plants and microorganisms.