Study On The Resistance Of OsAOS2,OsLOX3 And OsLOX4 To Rice Blast And Bacterial Blight

Rice is one of the most important food crops in the world.More than half of the world’s population chooses rice as the main food crop.Rice blast caused by Magnaporthe oryzae and bacterial blight caused by Xanthomonas oryzae pv.Oryzae(Xoo)are serious threats to rice yield.Therefore,it is particularly important to study the interaction mechanism between rice and pathogenic bacteria so as to cultivate disease-resistant rice.Phytohormones play an important role in the interaction between rice and pathogenic bacteria,and jasmonic acid,as an important activating signal molecule,can trigger plant immunity and confer plants with broad-spectrum resistance.Knockout or inhibition of genes on the jasmonate synthesis pathway can make plants less resistant to various pathogenic bacteria,and vice versa.As key enzymes in the jasmonic acid synthesis pathway,lipoxygenases(LOX)and allene oxide synthase(AOS)play important roles under biotic and abiotic stress in plants.AOS is the first key enzyme in the JA synthesis pathway.It has been reported that AOS2 can respond to the induction of Magnaporthe oryzae and enhance the resistance of rice to pathogenic fungi,but its mechanism of action has not been fully explored,and the resistance to bacteria disease has not been verified.As the second key enzyme synthesized by JA,has been verified to participate in resistance to fungi and bacteria in some dicotyledonous plants,but research on disease resistance in monocotyledonous plants,especially rice,is still quite limited.In this study,we used OsAOS2,OsLOX3,and OsLOX4 as research objects,and constructed knockout vectors for three genes using the CRISPR / Cas9 system.At the same time,we constructed overexpression vectors of those genes,and genetically transformed them to obtain transgenic plants,and selected homozygous mutations.Fungal and bacterial resistance analysis was performed in planta.q RT-PCR analysis showed that both Magnaporthe oryzae and Xanthomonas oryzae could induce the significant expression of these three genes in rice,and the expression levels of PR genes in the knockout transgenic plants of the three genes were significantly down-regulated.At the same time,the outbreak of reactive oxygen species induced by chitin and flg22 in the knockout transgenic plants was significantly reduced compared to the wild type.Inoculation experiments of Magnaporthe oryzae and Xoo showed that the knockout of all three genes reduced the resistance of rice to Magnaporthe orzyae and Xanthomonas oryzae.In contrast,overexpression transgenic plants of these three genes increased the expression of the PR gene and increased resistance to Magnaporthe orzyae.At the same time,after inoculation with Magnaporthe orzyae,the expression levels of SA pathway and JA pathway related genes were significantly down-regulated in the knockout transgenic plants of the three genes,while they were up-regulated in the overexpression transgenic plants.Thus,we suggested that OsAOS2,OsLOX3,and OsLOX4 may postively regulate rice resistance to fungi and bacteria by regulating SA and JA-mediated signaling pathways,and participate in the PTI pathway of rice.In this study,we initially clarified the functions of these three genes,laying a foundation for further revealing their involvement in rice disease resistance.