Study On The Regulation Of Conidial Germination And Appressorium Formation In The Ca²⁺ Signaling Pathway In Exserohilum Monoceras

As an important potential biological control agent,Exserohilum monoceras is a strongly pathogenic fungus of malignant associated weeds in paddy field,but safe to most crops such as rice and maize.In order to understand the infection mechanism of this bacterium,Fully explore the potential of the bacteria to control grasses,the signal conditioning during its pathogenicity was studied.In this paper,Ca²⁺signaling pathway was used to study its effect on the infection of Exserohilum monoceras.Barnyardgrass and rice were used as research materials.First,the Ca²⁺chelating agent EGTA,Ca²⁺channel inhibitor Verapamil,was used to suppress the Ca²⁺signaling pathway.The spore germination and appressorium formation were investigated under different conditions to confirm that Ca²⁺signaling pathway is indeed involved in the regulation of Exserohilum monoceras infection.Then,the infection behavior of Exserohilum monoceras on different substrates was investigated with the inhibitors EGTA and Verapamil to study the regulation of Ca²⁺signaling pathway on the infection of Exserohilum monoceras.The conclusions are as follows:（1）The inhibitory effect of EGTA on the spore germination and adhesion formation in the paraffin film was mainly manifested in the initial stage of conidia culture（0¹2 h）.This conclusion indirectly indicates that the Ca²⁺signaling pathway is essential for the spore germination and appressorium formation of Exserohilum monoceras,and the Ca²⁺signaling function mainly occurs in the early stage of fungal infestation（0¹2 h）.Inhibitor Verapamil can significantly inhibit the spore germination and appressorium formation behavior of Exserohilum monoceras,and the inhibitory effect mainly reflected in the early stage of fungal culture（1⁸ h）.When the concentration of the inhibitor Verapamil is sufficient,the germination of the fungal spores can be completely inhibited and the appressor cells are less able to form.It was demonstrated that Ca²⁺signaling pathway is essential in the germination stage of Exserohilum monoceras spores.（2）The infection behavior of Exserohilum monoceras mainly includes conidial germination and appressorium formation.The Ca²⁺signaling pathway plays an important role in both processes.Among them,appressorium formation process is more dependent on Ca²⁺signaling pathway and more sensitive in regulation.（3）After the inhibitor EGTA being used,Exserohilum monoceras can normally germinate on different substrates but cannot form appressoria,indicating that the Ca²⁺signaling pathway was involved in the formation of appressorium.The spore germination rate was significantly reduced in different substrates by the inhibitory Verapamil.The interdicted Ca²⁺signaling channels made the endogenous calcium store of the fungus not work,and then the spore germination rate decreased without Ca²⁺signal transmission,indicating that the Ca²⁺signaling pathway played an important role in the germination of conidiospores.（4）Ca²⁺signaling pathway and the physical and chemical properties of the substrate surface jointly affect the infection behavior of Exserohilum monoceras.Parafilm surface has no leaf surface structure,which is not conducive to the formation of appressorium,and is not conducive to the release of Ca²⁺from endogenous calcium stores in the event that Ca²⁺concentration is inhibited.The leaf surface of weeds is beneficial to the formation of appressorium and the leaf surface of rice is not conducive to the formation of appressorium.（5）Under different treatment conditions,the spore germination conditions of Exserohilum monoceras on different substrates are basically the same,indicating that the spore germination process is a relatively independent process.Exserohilum monoceras can form appressorium on Barnyardgrass leaf surface but can not form appressorium on rice leaf surface even without the inhibitor treatment,indicating that the formation of appressorium is more dependent on the external environment.According to the physical and chemical characteristics of leaf surface of different plant,targeting regulation of appressoria cell formation in the early infection stage of Exserohilum monoceras can effectively improve the weeding effect.