| Induced anti-herbivore resistance and primed anti-herbivore defense of plant are important functions of plant immune system.The induced anti-herbivore resistance is that the plant can produce a variety of defense responses after the herbivore infestation to form anti-insect characteristics through many changes such as the physiological,biochemical and morphological aspects.Primed anti-herbivore defense is a physiological process by which a plant prepares to more quickly or aggressively respond to herbivore attack.Primed state may be achieved in response to an environmental cue that reliably indicates an increased probability of encountering a biotic stress,such as necrotic pathogens,plant growth promoting rhizobacteria,but a primed state may also persist as a residual effect following an initial exposure to the stress.If infested by pests again,plants are able to resist pests stronger and more quickly to enhance anti-insect of plant more economical and effective.As one of the world's three major food crops,rice is a model plant for studying monocotyledon.It can form a clonal plant network by clonal ramet and spacer through clonal growth.Clonal plant networks have physiological integration function.Chemical and nutrients(such as photosynthetic assimilation product,mineral nutrients,water,etc.)can be transferred and sgared among individuals in the same clonal plant network.However,limited research exists in the integration function of defense on biological stress such as pests.In addition the signal transduction pathways of jasmonic acid(JA)and salicylic acid(SA)play an important role in rice resistance against monophagous pests such as Cnaphalocrocis medinalis(rice leaf folder,LF)and Nilaparvata lugens(brown planthopper,BPH).However,roles of the two signal pathways in plant defense priming are not clear yet.In this study,rice as the monocotyledon tillering plant is the object of study,and pests with different mouthparts(LF and BPH)and defense signaling chemicals(MeJA and SA)are applied to rice main stem(ramet of donor)to study the changes of enzyme activities and gene expression related to insect-resistant defense after the primary tiller(ramet of receptor)was induced or primed.The main results are as follows:(1)Weight gain of leaf folder(LF)larvae fed on primary tiller of wild-type rice was significantly lower than that in the control group after main stem had been induced by LF feeding or MeJA treatment for 2 d.When OsCOI1 is silenced,the result showed that it has no significant effect on the resistance to LF,showing that the LF feeding or hormone applied to donor(main stem)induced and activated the jasmonate-signal transduction pathway in the receptor(primary tiller),and increased the resistance to LF.(2)After main stem(donor)had been induced by LF feeding or MeJA treatment for 2 d,when primary tiller(receptor)of the wild type rice plants was infested by LF,the PPO,POD,LOX enzyme activity,the content of JA and TrypPI in the leaves related to jasmonate-signal transduction pathway were significantly higher than those of primary tiller(receptor)of the wild type rice plants without induction.The defense genes related to JA pathway like OsCOI1,OsLOX,OsAOC,OsAOS and the Trypsin inhibitor synthase gene(OsBBPI)were overexpressed,showed that related defense system was initiated by the pests feeding or hormone treatment of donor,and defense system of primary tiller was also initiated by clonal plant network,which induced its insect resistance.But for rice plants of OsCOI1 RNAi,the PPO,POD enzyme activity,JA and TrypPI content and OsCOI1 gene expression quantity of rice in treatment group had no significant difference compared with complete blank control group and the control group that the main stem was not treated but the primary tiller was eaten,but the activity of LOX enzyme increases.The OsAOC,OsAOS and OsBBPI genes in the two treatment groups had over expression compared with complete blank control group,but there was no significant difference compared with the control group that the main stem was not treated but the primary tiller was eaten.The results showed that the silencing of OsCOI1 gene blocks the signal transduction pathmway of JA,which affected the transmission of defense signal and the activation and regulation of OsCOI1 plants primary tiller defense system.Although there were significant differences on part defense enzymes and genes compared with the control group,the anti-insect of primary tiller was not improved on the whole,and the defense was not faster and stronger.Proved that whether the receptor can get systemic induction resistance from donor to enhance the resistance to LF depends on the activation and regulation of JA signal transduction pathway.In addition,PAL enzyme activity decreased and SA content did not increased for rice plants of wild type and OsCOI1 RNAi in the experience,which showed when the rice plants were infested by chewing pests,it did not use SA signal transduction pathway for defense,and there was antagonistic relationship between SA signal transduction pathway and JA transduction pathway.(3)After main stem(donor)had been induced or primed by BPH feeding or SA treatment,the honeydew amount secreted by BPH that ate the induced primary tiller was significantly lower than that of the control group(P<0.05),and the honeydew amount secreted by BPH that ate the primed primary tiller has also reached a significant effect(P<0.01),which showed that BPH infestation or hormone treatment on the donor of rice clonal plant network could induce or prime the insect resistance or warning ability of the receptor(primary tiller).In addition,part of the activities of defense enzymes,rising range of SA content and rising multiples of part genes in experience of primed defense response were higher than that in experience of induced defense response,which showed that receptors obtaining defenses warning ability by priming was stronger than those by inducing in the face of pests infestation.(4)After main stem(donor)had been induced or primed by BPH feeding or SA treatment,when primary tiller(receptor)was infested by BHP,the activity of PAL,POD,LOX defense enzyme activity in leaf sheath,the content of JA,SA and TrypPI,the expression levels of OsPAL genes related to SA signal transduction pathway,OsCOI1?OsAOC?OsAOS?OsLOX genes related to JA signal transduction pathway,OsPR1?OsNPR1 protein genes related to pathogeny,OsBBPI of trypsin inhibitor synthase gene and OsWRKY70 gene related to transcription factor were significantly higher and quicker than those of the control group,which showed that the BPH feeding o SA applied to donor(main stem)can induce and prime the insect resistance and warning ability of primary tiller in clonal network,activate the related defense signal pathway more quickly in anti-insect,regulate the rice plants against pests,and showed faster and stronger anti-insect defense.In addition,expression quantities of part of defense enzyme activity,hormone content,defense gene related to JA and SA signal transduction pathway were increased or upregulated in the experiment,which not only proved that JA,SA signal transduction pathways were involved in the regulation of synthesis of these defense enzymes and hormones,but also showed that the two signal transduction pathways were involved in the defense of BPH in rice clonal network,reflected the relationship of mutual promotion.The results showed that there was a defense signal communication network between rice clone plants,and when a clonal ramet was infested by pests,the rice would initiate the defense signal communication network between the clone plants and activate the antiherbivore defense response of other clone plants in the clonal network system,so that it could induce the systematic resistance of rice clone network and make the rice in the warning state of primed anti-herbivore defense(prime state).When in face of infestation,it would show stronger insect resistance,and these defenses mainly depend on the activation and regulation of JA and SA signaling transduction pathways.The study showed the chemical communication between different clone plants of rice,and induced defense signal and transmission mechanism of rice clonal plant network,which was of great significance to clarify the more hierarchical interactions between ecological functions of clonal plant networks,and population dynamics and community structure of clonal plant,and provides theoretical basis for control of pests by clonal plant's own resistance system and developing new strategies for anti-insect genetic engineering. |
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