| Rice(Oryza sativa L.)is one of most important economic and food crop in the world.The consumption of rice plays a leading role in China’s food crops.To make sure the stability and high yield of rice production has a very important strategic position in ensuring food security.At the same time,the global environment is getting warmer and warmer,and extreme climate occurs frequently which will bring many unpredictable risks.Therefore,on the basis of ensuring and increasing rice yield,the ability of-rice to resist abiotic and biotic stresses should be further studied and discussed.Rice Xa21,which was cloned in 1995,belongs to a receptor kinase during the immune system.It has broad-spectrum resistance to Xanthomonos oryzae pv.Oryzae(Xoo).Pathogenesis-related proteins(PR)are a kind of low molecular weight proteins produced by plants infected by exogenous pathogens or abiotic stress.Rice OsPR1 family belongs to Serine carboxypeptidase-like proteins(SCPLs),which are found in rice,tobacco and tomato.OsPR1A is one of the earliest pathogenesis-related protein to be identified and cloned.which is probably involved in the signal pathway of rice Xa21-mediated resistance to bacterial blight.There are three purposes in this study:Firstly,the effects of OsPR1A on agronomic traits of rice and the expression of OsPR 1A under abiotic stress were studied.Secondly,the relationship between OsPR1 A and light response were studied.Thirdly,OsPR1a-RNAi and OsPR1a-OX transgenic plants were constructed and obtained in order to reveal the relationship between OsPR1 A and the resistance response against to bacterial leaf blight mediated by Xa21 and finially to achieve the long-term goal of non-Xa21 dependent,non-Xoo race dependent,non-temperature and developmental period dependent resistance.Fourthly,the transcription of OsPR1 a gene in different parts and different growth periods and the function analysis of OsPR1a gene during the process of growth and development were studied and discussed.OsPR1a-RNAi and OsPR1a-OX vectors were constructed by transforming OsPR1a-RNAi and OsPR1a-OX plasmids into 4021(Xa21+)and positive homozygous plants were obtained.Compared with the wild type,the transgenic plants of OsPR1a-RNAi and OsPR1a-OX decreased in plant height,spike length,tiller number and seed-setting rate.The influence of RNAi and over-expressionn on the above agronomic characters was different,RNAi was even worse.Rice seedlings were treated with cold,heat,drought,submergence,salt and different light treatments.The whole protein was extracted and analyzed by WB and then the expression of OsPR1A under the obove abiotic stress was analyzed.It was found that the expression of OsPR1A in different stress showed different trends,especially the response to light,the expression of OsPR1A increased gradually under full light,kept stable under the half day and half night and decreased gradually in the dark environment.The expression of OsPR1A in the shading part was lower than that in the non-shading part and was similar in vitro to that in vivo.In order to investigate the function of OsPR1A in Xa21-mediated disease resistance pathway,TP309,4021,OsPR1a-RNAi and OsPR1a-OX plants grown in the field at tillering stage were inoculated with Xoo.The result showed the resistance response was not significantly different because of the strong resistance of rice plants at this stage.And then TP309,4021,OsPR1a-RNAi and OsPR1a-OX plants grown in greenhouse at seedling stage inoculated with Xoo.The result showed that the length of lesion was TP309>OsPR1a-RNAi>4021>OsPR1a-OX.The number of Xoo cells detected by WB was TP309>OsPR1a-RNAi>4021>OsPR1a-OX.It can be seen that the length of lesion and the number of Xoo cells were in the direct ratio.The expression level of OsPR1A was OsPR1a-OX>4021>OsPR1a-RNAi>TP309.This proved that the expression level of OsPRIA was inverse proportional relationship to the lesion length and Xoo cell number.OsPR1A started rapidly in the resistant combination(4021-Xoo)and was rapidly detected on the 2nd day after inoculation.In the susceptible combination(TP309-Xoo),OsPRIA expression was detected on the 8th day after inoculation,and then increased violently.With the further invasion of Xoo.the expression of OsPR1 A was induced in large quantities.But at this time.OsPRI A could not restain Xoo from further infection,so rice showed susceptible phenotype.It can be concluded that the resistance and susceptibility of rice are closely related to the time of OsPR1A expression.In order to further clarify the location of OsPR1A expression,rice leaves were collected on the 6th day of inoculation based on the lesion line.The results showed that the expression of OsPR1A appeared at I cm above and 1 cm below the lesion line,and the farther away from the lesion line,the lower the expression of OsPR1A.The resistance reaction mediated by Xa21 was closely related to the development stage and growth temperature.Under the condition of 27℃.the rice seedlings showed full resistance when inoculated with Xoo.When transferred to 31℃.it became susceptible and losed the gained resistance.Xa21-mediated resistance can be fully activated when the juvenile plants were grown at 27℃.Xa21 immune response mechanism will be greatly promoted by this study.In conclusion.OsPR1A plays an important role in rice light response,Xa21-mediated resistance response to Xoo and non-Xa21-dependent resistance response. |
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