Jasmonic Acid-and Ethylene-induced Mitochondrial Alternative Oxidase Stimulates Marssonina Brunnea Defense In Poplar

Plant mitochondrial processes are involved in plant response to biotic stress caused by viruses,actinomyces,bacteria,and pests.Previous studies have shown that the mitochondrial alternate respiration pathway plays a positive role in plant resistance to biotic stress,but the mechanism of its resistance to fungal infection remains unclear.In the present study,we studied function and regulation of mitochondrial alternative oxidase(AOX)in poplar against Marssonina brunnea,and we aimed to explore the role of mi ETC in the poplar leaf exposed to M.brunnea.We devised an in vitro interaction system of poplar leaf challenged with M.brunnea,employing microscopy and chlorophyll fluorescence(CF)Pulse-Amplitude-Modulation(PAM)imaging system to evaluate the fungal infection;and then used exogenous respiratory inhibitors to investigate the function of mi ETC and its regulatory mechanism,which provided some theoretical basis for the subsequent study of poplar resistance to black spot disease.The main results of the experiment are as follows:(1)mi ETC and phytohormones participate in poplar response to M.brunnea infection.M.brunnea inoculation induced the transcript amount of AOX1 a gene in the mitochondrial electron transport chain(mi ETC)and the biosynthetic genes of jasmonic acid(JA)and ethylene(ET)with accumulation of these phytohormones in poplar leaf,while inhibiting the transcript amount of mitochondrial cytochrome c oxidase gene(COX6b)and genes related to salicylic acid(SA).(2)AOX plays a positive role in the response of poplar to the stress of M.brunnea,and AOX reduces the sensitivity of poplars to M.brunnea by increasing the ATP/ADP ratio,while inhibiting the alternate breathing pathway has the opposite effect.(3)The effect of exogenous JA and ACC on mi ETC and cyanide metabolism was similar to that of pathogen inoculation.Exogenous JA and ACC induced the defense effect of poplar against M.brunnea by enhancing the expression of AOX1 a gene and inhibiting the expression of Cox6 b gene.JA and ACC upregulate AOX in the defense response of poplar to M.runnea.Exogenous JA and ACC may increase cyanide content by reducing the expression of genes related to cyanide metabolism.These results indicate that JA and ACC induce AOX pathway to increase ATP/ADP ratio to maintain plant energy efficiency,thus enhancing poplar defense response to M.brunnea,and cyanide may be involved in the induction of AOX by JA and ET.The results of this study deepen the understanding of the interactions between plant pathogenic fungi and provide a theoretical basis for molecular breeding of poplar resistance.