OsDLT Regulation And Mechanism Analysis Of BPH Resistance

Brassinosteroids(BR),one of plant sterol hormones, plays important roles in plant various progresses such as growth, development and response to environmental stresses, which widely exists in plant roots, stems, leaves, pollen and seeds, and other organs. However, in rice little is known about the role and mechanisms of BR biosynthesis and signaling pathway in induced resistance to herbivores. OsDLT encodes a GRAS family transcription factor, and acts as a positive component of BR signaling in rice development. In order to elucidate the role of OsDLT of BR signaling pathway in rice induced defense responses to insect, we use the system of rice and its major insect pest the brown planthopper(Nilaparvata lugens Stal, BPH) to reveal function and mechanism of OsDLT in herbivore-induced defense responses of rice against herbivores.The results are as follows:(1) qRT-PCR results indicated that mechanical wounding and BPH treatment repressed expression of OsDLT significantly at early but latterly rapidly increased the mRNA levels of OsDLT; SSB infestation and JA treatment resulted in an obvious increasing transcript levels of OsDLT; Transcript accumulation of OsDLT were suppressed significantly by SA treatment.(2) OsDLT and its mediated BR signaling negatively regulated BPH-induced direct defense in rice. Rice of dlt was loss-of-function of OsDLT in rice, compared to wild type 9311 rice, gravid female BPH adult preferred to feed on and oviposite on dlt; Nymphs fed on dlt rice have lower survival rate and emergence rate, with decreasing developmental speed compared to these fed on 9311 rice; also fresh emerged BPH adults from dlt rice gained little weight and produce less honeydrew in composing to these from 9311 rice. Eggs developmental speed on dlt laid by BPH colony from dlt rice were more slower than which on 9311 laid by BPH colony from 9311 rice.(3) OsDLT positively modulated BPH-induced indirect resistance of rice, The ratio of parasited BPH eggs on dlt rice in field and in room both were significantly lower than that of wild type rice plants and in corresponding with lower attractive activity to wasp of Apanteles nilaparvatae.(4) All transcript levels of WRKYs teanscription factors OsWRKY30, OsWRKY45,OsWRKY53, OsWRKY70 and OsMPK3, OsMPK6, OsMPK7 in BPH-infested dlt significantly increased comporison to the same treated wild type 9311. dlt rice elevated BPH-elicited jasmonic acid (JA) and jasmonoy-isoleucine (JA-Ile), TrypPIs, and wounding-induced GLVs(cis-3-hexenol), transcript levels of OsHI-LOX and OsAOS).(5 ) In addition to oxylipin pathway, rice mutation in OsDLTresulted in increasing BPH-induced production of H2O2 which generated from NADPH-oxidase dependent pathway but decreasing BPH-induced emission of ethylene. However, for BPH-induced indirect defense, dlt rice showed lower levels of constitutive and BPH-induced plant volatiles including aromatic compounds, mono- and sesquiterpenes.In conclusion, OsDLT modulated BR signaling at different levels of gene transcript, protein activity, and secondary metabolic compounds by integrating signaling pathways of at least ROS,oxylipins and ethylene, MAPK. Furthermore OsDLT and its mediated BR signaling play roles in plant growth and development, so OsDLT might be an essential trade-off modulator of BR signaling between growth and resistance in rice.