The Functional Analysis Of OsC₂H₂-19 Transcription Factor Involved In Resistance To Brown Planthopper From Rice

Rice is the most important crop in our country,and its production is closely related to the food security.The brown planthopper(BPH),Nilaparvata lugens,is one of the most destructive pests in rice production worldwide,causing tremendous rice yield losses.More than 3000 transcription factors(TF)have been identified from rice genome,which play important roles in defensing against pest and disease damage.The most economical strategy to control this pest is to grow resistance rice varieties.However,very few resistance TFs have been previously cloned and the molecular mechanisms of TF-mediated rice resistance to the BPH have not yet been elucidated,which seriously inhibiting the identification of resistance genes and the breeding of resistance rice varieties.Previously,we constructed TF-overexpressed and-repressed transgenic rice.To identify BPH-resistance TFs,we examined the transgenic rice lines for BPH-resistance using the bulked seeding test and found that C2H2-overexpressed transgenic lines showed decreased resistance to the BPH.In addition,we compared the differences of physiology and defense pathways between wild type(WT)and transgenic lines in response to BPH infestation.The goal of this study is to explore the molecular mechanisms of C2H2 TF-mediated rice resistance to the BPH,and to provide theoretical foundation for the use of resistance genes in rice breeding.The main results are list below:1.We randomly selected twenty transgenic lines to examine BPHresistance using the bulked seeding test on the basis of the TFoverexpressed and-repressed transgenic rice obtained previously,and found a C2H2-overexpressed transgenic lines were susceptible to the BPH.The number of BPHs that settled on the transgenic plants were significantly lower than that of wild type in the host choice test.The population growth rates,survival rates,and honeydew excretion were significantly higher on the transgenic plants,compared with the wild-type plants.These results suggested that this OsC2H2-19 TF of rice might be participated in the resistance against BPH.2.Next,we examined the activity of protective enzymes of susceptible transgenic lines and wild-type plants in response to BPH infestation.The enzyme activities of catalase(CAT),peroxidase(POD),polyphenol oxidase(PPO)and superoxide dismutase(SOD)were significantly increased in both transgenic and wild-type plants after BPH infestation.However,the inductive effect of enzyme activity in wild-type plants was significantly higher than that in transgenic lines,which suggesting that this OsC2H2-19 TF may be a suppressor in the process of resistance against BPH.3.We also examined the transcript levels of defense-responsive genes involved in the salicylic acid(SA)-dependent pathway.The results showed that BPH infestation could induce the expression of SA synthesis-related genes and SA receptor NPR1.The inductive effect of these genes and SA content in transgenic lines were significantly lower than that in wild-type plants.Interestingly,the resistance levels were elevated in OsC2H2-19 transgenic lines after application of SA.These results suggested that this OsC2H2-19 TF may work through SA synthesis to regulate resistance process in rice after BPH feeding.