| Rice is one of the most important food crop worldwide.However,invasion of pathogens is a serious threat to the production and quality of rice.Bacterial leaf streak,a bacterial disease caused by Xanthomonas oryzae pv.Oryzicola,Xoc,has been becoming the main disease in the rice-growing areas of West Africa,South and Central China gradually.Resistance to bacterial leaf streak disease is a typical quantitative trait.Nevertheless,owing to the lack of rice resources carrying main disease resistance genes of bacterial leaf streak disease,it is important to search potential resistance genes to cultivate disease-resistant varieties to resist bacterial leaf streak disease.Our previous studies compared the differentially expressed genes in a high resistance rice material Acc8558 and a susceptible rice material ZH11 to bacterial leaf streak disease,and selected OsDRxoc1 gene(LOC_Os05g37060)located at the qBlsr5 b which is a greatly resisitant to bacterial leaf streak area as the research object for further study.Through analyzing and identifying the structure and function of OsDRxoc1,it was confirmed that OsDRxoc1 could encode the transcription factor of R2R3-MYB protein,and could be induced expressing by pathogenic bacteria.When inoculating the T0 and T1 generations of OsDRxoc1 transgenic rice with ZH11 as background,it was found that OsDRxoc1 overexpressed rice increased its resistance to Xoc RS105,whereas OsDRxoc1 suppressed rice showed more sensitive to RS105.Here,this paper carried out further research on the molecular mechanism of OsDRxoc1-mediated resistance to bacterial leaf streak.We found that the leaves of OsDRxoc1 overexpressed transgenic rice were more yellow than the wild type which due to the decrease of the content of chlorophyll and carotenoid in the leaves.The transmission electron microscope showed that the structure of the chloroplast was changed obviously that both of the length and number of layers of the substrate sheet were reduced,suggesting that OsDRxoc1 is closely related to the structure of the chloroplast.Meanwhile,we found that OsDRxoc1 was able to quickly respond to inducing of SA but not GA or JA when spraying with hormone on rice.Consistent with these results,the hormone content of JA,JA-Ile and SA content were also increased in OsDRxoc1 overexpressed rice compared with the wild type,especially with the RS105 inoculation.These results suggested that the resistance to bacterial leaf streak in rice mediated by OsDRxoc1 may due to theregulation of JA and SA content which adjusted by corresponding JA and SA signaling pathway.In order to analyze how OsDRxoc1 participates in the interaction between rice and pathogens,yeast two-hybrid screening was used to screen for putative OsDRxoc1 interacting proteins and OsbHLH81 was obtained.Compared to that in the wild type,OsbHLH81 was down-regulated significantly in OsDRxoc1 overexpressed transgenic rice,suggesting that OsDRxoc1 regulates the expression of OsbHLH81 negatively.Disease resistance test also showed that OsbHLH81 overexpressed rice increased the susceptibility of rice to bacterial leaf streak,while OsbHLH81 suppressed transgenic rice performed a resistant phenotype to bacterial leaf streak,indicating that OsbHLH81 works as a negative regulator in the resistance of rice to bacterial leaf streak.In addition,JA signaling pathway genes were activated in OsbHLH81 suppressed rice,suggesting that the signaling pathways for OsDRxoc1 and OsbHLH81 regulating may be related to JA.In summary,OsDRxoc1,as a positive regulator of rice resistant to bacterial leaf streak disease,can activate the SA signal pathways,and regulates the JA signal pathway positively through interacting with OsbHLH81 in rice to achieve resistance to pathogenic bacteria.This study reveals the molecular mechanism of rice resistance to bacterial leaf streak disease which has guiding significance for breeding disease-resistant varieties,and also be helpful to further explore the relationship between plant chloroplast development and the interaction with pathogens. |
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