The Role Of Abscisic Acid In The Interactions Of Rice Stripe Virus With Rice(Oryza Sativa)

Rice stripe,which is caused by Rice Stripe Virus(RSV) is the most widely distributed rice virus disease in China.It has an increasing epidemic tendency in recent years and rice productivity has been greatly influenced.Resistant cultivars provide the most environmentally safe,reliable,and cost effective means of controlling virus diseases.Understanding the molecular mechanism of RSV will provide us with the basis for effective engineering strategies to increase resistance.Phytohormone abscisic acid(ABA) is a signal molecule in regulation of plant defence responses to biotic stress, such as pathogen attack.ABA has been implicated in determining the outcome of interactions between many plants and their pathogens.The role of ABA in the interactions of RSV with host rice has not been reported yet.Results showed that some ABA related genes responded to RSV stress,including those ABA-responsive genes, ABA biosynthetic genes and ABA mediated signaling genes(unpublished data).It suggested that ABA was possibly involved in the regulation of rice defense responses to RSV attack.Two japonica rice cultivars(line),Wuyujing No.3 and KT95-418 were utilised to reveal the role of ABA in the interactions of RSV and host rice.The resistance identification to rice stripe showed that Wuyujing No.3 was susceptible,while KT95-418 had medium resistance.Exogenous application of ABA to Wuyujign No.3 prior to or during inoculation with RSV resulted in a decline in incidence rates, alleviation of stripes in rice leaves and a delay in the leaf symptoms,however,the effects varied with the application of ABA to infected rice seedlings with stripes.The influence of ABA and ABA biosynthetic inhibitor,norflurazon on the expression patterns of the coat protein(CP) gene of RSV was quantified using Real-time quantitative reverse-transcription PCR(RQ-RT-PCR),respectively.ABA suppressed the expression of CP gene in Wuyujing No.3,and did not affect CP gene expression in KT95-418.Norflurazon had no effect on CP gene expression in both Wuyujing No.3 and KT95-418. Endogenous ABA level in rice plants under RSV stress was evaluated by using high-performance liquid-chromatography.ABA in Wuyujing No.3 and KT95-418 both increased,and decreased as the time longer,the increase of ABA levels were sustained longer than that in Wuyujing No.3.The mRNA transcript levels of the ABA receptors FCA,ABAR and GCR2 under RSV stress were analyzed by using RQ-RT-PCR.FCA and GCR2 expressions in Wuyujing No.3 and KT95-418 were both up-regulated,however,ABAR expression wasn’t affected.It was suggested that FCA and GCR2 receptor was possibly involved in the regulation of plant defense response signaling besides their known functions.Nine ABA-related genes,Polcalcin(Polealcin Jun o 2),OsCIPK15(CBL interacting serine/threonine-protein kinase 15),OsGASA2(Gibberellin-regulated protein 2 precursor),WGP1(BURP domain containing protein),OsCBL4(Calcineurin B-like protein 4),Myb(typical P-type R2R3 Myb protein),HLH(Helix-loop-helix DNA-binding domain containing protein),CaM(Calmodulin-like protein 1) and C3HC4(Zinc finger,C3HC4 type family protein) in susceptible and resistant rice varieties(line) were analyzed under RSV stress by using RQ-RT-PCR.The results showed that all the above nine genes in susceptible rice plants were up-regulated; whereas,in resistant rice plants,OsGASA2 and OsCIPK15 genes were down-regulated, Polcalcin,CaM and Myb genes were up-regulated,and the transcript levels of WGP1, HLH,C3HC4 and OsCBL4 genes remained constant.ABA-related genes were induced after Application with ABA.Therefore,it was considered that the ABA-related genes were regulated by ABA in the susceptible and resistant rice varieties under RSV stress.An observation had been made on the callose deposition in leaves of resistant rice variety line KT95-418 and susceptible rice variety Wuyujing No.3 under RSV stress via freehand sectioning and aniline blue staining.Results showed that callose fluorescences in leaves of Wuyujing No.3 under RSV stress remained constant compared with the uninoculated control;however,the leaves of KT95-418 under RSV stress had more callose staining,including large vascular bundles and sclerenchyma cells of vascular bundle sheath,small vascular bundles,epidermal cells and mesophyll cells;and more fluorescence of callose deposition were observed in resistant varieties than susceptible varieties.It was considered that callose deposition and resistance was positively related.The coding sequences of two genes encoding the serine/threonine kinase-like protein and 33 kDa secretory protein were cloned,respectively.This thesis showed that ABA played a regulatory role in rice defense against RSV.